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Evolution
Evolution
Why Do Animals Survive or Die?
Natural selection means that there are random differences in characteristics that organisms
inherit from their parents. These characteristics may give individuals an advantage or disadvantage
compared to others in surviving and reproducing. The advantaged offspring are more likely to
survive and reproduce. In this way, there will be more of the organisms with advantageous
characteristics. When an environment changes, characteristics that give an organism an
advantage may change.
True or False?
1. Natural selection is a complicated theory that scientists still don't understand T / F
2. Organisms that have the best characteristics for their environment survive T / F
3. When the environment changes, what makes for an advantage can change T / F
About Natural Selection
Natural selection exists everywhere. If you are
into sports, then you already know that you have to
be a good team to win the Super Bowl, NBA Finals, or
the NCAA Championship.
From your everyday
experiences, you know that the stores in East
Cleveland will only survive if they do good business.
The stores that have prices that are too high, things to
buy that are of low quality, or are not well maintained
will fail.
Sports teams and stores on the street are both
excellent examples of natural selection, even though it
may not seem like it at first! You may think that some scientist came up with some very
complicated and hard to understand theory, but natural selection is actually the simplest
explanation of what has been going on for billions of years. If you do well, you survive, if you
don't, then you die.
Going back to sports, if the Cleveland Browns (magically) won the
Super Bowl this year, that would mean that they were a good team. It
doesn't matter what you think, but because they out-competed all of the
other teams, that means that they played the game better than those
teams. It's important to realize that natural selection isn't about what
scientists think should happen, it's about noticing what does happen. So,
if the Browns win the championship, they are a good team. Furthermore,
if they win, then companies will want to give them money so that the
company can be associated with a “winner”. With this money, the Browns
can improve their training, their stadium, or go out and get better players.
This means that because they won, they will be better prepared for the
future.
Natural selection says that the best organisms will survive and reproduce more individuals
like themselves. The weakest individuals die and do not get to reproduce; this means that the
individuals left behind are the strongest, not the weakest. In a population of wild cats, the cats
that are able to hunt the most birds survive and produce kittens; the cats that are unable to hunt
birds die.
Going back to the stores, if Bob's Discount Gas offers gas for $3.00 a gallon, even though it
costs them $3.50 a gallon, then they will eventually go out of business. This means that the other
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Why Do Animals Survive or Die?
gas stations will benefit and get more money that people aren't spending at Bob's. The weakest
die off, leaving the strongest with the rewards.
When scientists are talking about living things and natural selection, there are a few key
terms that are used in order to make things easier. The individuals that have characteristics which
make them stronger than the others are the advantaged offspring (in the example, this would be
the Browns).
The characteristics that make them stronger are called advantageous
characteristics. Again, it doesn't matter what you think is a better characteristic – it all depends
on what ends up helping an organism survive and reproduce!
Even more importantly, what happens when the game changes? In other words, what
happens if the NFL decides to make the field 20 yards longer, the NBA decides to move the 3-point
line to half-court, or the NCAA decides that the shot clock should be 24 seconds instead of 35
seconds? These are all changes in the environment. You can imagine that different teams would
do better under these circumstances. The same thing would happen to Bob's Discount Gas if all of
the other gas stations went out of business; all of a sudden, they would be doing very well because
they could set whatever price for gas that they wanted! If the environment changes, then some
characteristics that did not help the organism before may now be advantageous. If suddenly there
are no birds for our wild cats to hunt, then the cats that are better mouse hunters will survive
better and reproduce more good mouse-hunters.
True or False?
1. Natural selection is a complicated theory that scientists still don't understand T / F
2. Organisms that have the best characteristics for their environment survive T / F
3. When the environment changes, what makes for an advantage can change T / F
Questions
Do you remember?
1. Define natural selection in your own words.
2. Which are the advantaged offspring?
3. Why doesn't it matter what scientists think about natural selection?
Think about it!
4. Describe an advantageous characteristic using an example of your own.
5. Select one sports team that you think will win this year. Explain why!
Do something!
6. Create a change in the environment East Cleveland. Predict at least three stores that will
survive and three stores that will go out of business because of this environmental change.
Remember?
7. Describe homeostasis in your own words.
8. How was Earth formed?
9. What protects the Earth from UV rays?
London's Peppered Moths
Vocabulary
Predominant In the majority
Fitness Ability to survive; well-adapted to the environment
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Evolution
Textile
Catalyze
Agriculture
Soot
Lichen
Mechanism
Genetic Diversity
Directional Selection
Cloth and other materials to make clothing
To help to bring about
Farming
Ash, the remains of things that have been burned
A combination of a fungus and an algae that help each other (mutualism)
Way that something works
The amount of differences in characteristics within a population
Natural selection moves characteristics in a particular direction
A Case Study in Natural Selection
By Laura Klappenbach, About.com
In the early 1950's, H.B.D. Kettlewell, an English physician with an interest in butterfly and
moth collecting, decided to study the unexplained color variations of the peppered moth.
Kettlewell wanted to understand a trend that had been noted by scientists and naturalists since the
early nineteenth century. This trend, observed in the industrialized areas of Britain, revealed a
peppered moth population—once primarily made up of light gray-colored individuals—that now
consisted primarily of dark gray individuals. Kettlewell was intrigued. Why had this color variation
taken place in the moth population? Why were dark gray moths more common only in industrial
areas while light gray moths were still predominant in rural areas? What do these observations
mean?
Why Had This Color Variation Taken Place?
To answer this first question, Kettlewell set about the task of designing several experiments.
He hypothesized that something in industrial regions had caused the dark gray moths to be more
successful than the light gray individuals. Through his investigations, Kettlewell established that
dark gray moths had greater fitness in the industrial areas than light gray moths. He was able to
attribute this increased fitness to the dark gray moths' ability to better blend into their habitat and
avoid predation by birds.
Why
Were
Dark
Gray
Moth
s
More
Com
mon
in
Indu
strial
Area
s
While Light Gray Moths Were Still Predominant in Rural Areas?
Once Kettlewell had completed his experiments, the question remained: what had changed
the moth's habitat in industrial regions enabling darker colored individuals to blend in to their
surroundings better? To answer this question, we can look back into Britain's history. In the early
1700's, the city of London—with its well-developed property rights, patent laws, and stable
government—became the birthplace of the Industrial Revolution.
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Why Do Animals Survive or Die?
Advancements in iron production, steam engine manufacturing, and textile production
catalyzed many social and economic changes that echoed beyond the city and altered the future of
what had been, until then, a primarily agricultural workforce. Great Britain's plentiful coal supplies
provided the energy resources needed to fuel the fast-growing metalworking, glass, ceramics, and
brewing industries. Because coal is not a clean energy source, its burning released vast quantities
of soot into London's air which settled as a black film over the city.
In the midst of London's newly industrialized environment, the peppered moth found itself in
a difficult struggle to survive. Soot coated and blackened the trunks of trees throughout the city,
killing lichen that grew on the trees and turning the bark from a light gray-flecked pattern to a dull,
black film. The light gray, pepper-patterned moths, that once blended into the lichen-covered bark,
instead stood out as easy targets for birds and other hungry predators.
About Natural Selection
The theory of natural selection
suggests a mechanism for evolution and
gives us a way to explain the variations we
see in living organisms and the changes
evident in the fossil record. Selection
processes can act on a population to either
reduce genetic diversity or to increase
genetic diversity. The types of natural
selection (also know as selection strategies)
that reduce genetic diversity include:
stabilizing
selection
and
directional
selection.
The selection strategies that increase
genetic
diversity
include
diversifying
selection, frequency-dependent selection,
and balancing selection. The peppered moth
case study described above is an example of
directional selection: the frequency of color
varieties changes dramatically in one
direction or another (lighter or darker) in
response to the predominating habitat conditions.
Lichen attached to a rock
Respond
1.
2.
3.
4.
5.
6.
What did H.B.D. Kettlewell observe?
Why was there a difference in fitness between the two colors of moths?
Why were dark-colored moths surviving better than light-colored moths?
What are the five types of natural selection mentioned in the article?
Why is this an example of directional selection?
In the 20th century, London began to clean up its industrial pollution, to the point where the
trees returned to their normal colors. What effects do you think this had on the moth and
bird populations? Be specific!
Activities
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Evvoolluuttiioonn
Watch the Evolution video and answer the following questions:
1. What is the most “interesting,” principal evidence for evolution?
2. Name one difference and one similarity between whales and humans.
3. What land mammal did whales start as?
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TThhee G
Grreeaatt FFoossssiill FFiinndd
Answer all questions on a separate sheet of paper, in groups of 3 – 4!
In this activity, you and the members of your team will play the roles of paleontologists working
in the field in Ohio, near the town of Canton. One clear crisp afternoon in October, you find four
well-preserved and complete fossil bones.
1. Withdraw four fossil bones from your envelope. Make sure you take them out without
looking at the ones remaining in the envelope!
It is too late in the day to continue with the dig, so you return to camp with your find. That
night, in camp, after dinner, around a lantern, you and your colleagues begin to assemble the 4
bones you found earlier. Since the bones were all found together and in an undisturbed layer,
you assume that they are all from the same animal. You spend the rest of the evening trying
different arrangements of the bones in hopes of identifying the animal.
2. Use the next 3-5 minutes to try various combinations.
As the night wears on, you get weary and decide to retire and begin anew in the morning.
3. What kind of animal do you think it could be?
Ohio mornings are marvelous. They are clear, cool, and clean. Just the kind of day you need to
get work done at the dig. The rock layers that hold your fossils are very hard and only grudgingly
give up three more specimens. With the day at an end, you make your way back to camp for
another try at assembling this mystery animal.
4. Withdraw 3 more bones from the envelope. Use the next 3-5 minutes to incorporate your
new finds in your fossil reconstruction.
It's getting late, and you are getting weary. Maybe tomorrow you will find the answer to the
puzzle.
5. What kind of animal do you think it could be now?
The next day is cold. It is the last day of the digging season. Winter lurks behind the hills, and
you must leave. Just as the day is about to end in disappointment and defeat, one member of
the group cries out "I've got them! I'VE GOT THEM!"
6. Withdraw 3 more bones from the envelope. Use the next 3-5 minutes to incorporate these
latest finds. Record what you think it is now.
Back in the lab at East Cleveland, you go searching in the resource library, and you find some
partial skeleton drawings from another group working at a different location but dealing with the
same geological period. They have found a skeleton similar to yours, but with some additional
bones that you don't have. You use this information to add to your own data.
7. Take the next 3-5 minutes to compare your findings with those of a team near you,
looking for clues that might help you in your reconstruction, and possibly even suggest an
entirely different animal than your earlier ideas. Apply these latest clues to the assembly
of your skeleton as best you can. Record the type of animal suspected now. Be as specific
as you can.
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Why Do Animals Survive or Die?
Once you are back in your own laboratory at Shaw High School, you find a Skeletal Resource
Manual with drawings of the skeletons of some existing animals. You notice some interesting
similarities between some of the drawings and your unknown fossil.
8. Use any resources you can find to assist you in your final assembly of the fossil skeleton.
Record your final interpretation:
9. Be sure that all envelopes (with their bones) and Skeletal Resource Manuals get returned.
10. Share your results with the whole class.
11. Is there general consensus on what the creature was? If so, discuss what the most telling
clues were. If not, what was the main source of conflict?
12. Did you make any assumptions or inferences at the beginning of the activity that kept you
from assembling the "right" skeleton (i.e. your final interpretation)? Explain.
13. Did the discovery of new bones cause any conflict within your group? Explain.
14. Did any of your group members resist changing in light of the new information? Explain.
15. Did the information from another group influence your assumptions? If so, what info?
16. Did the resource booklet confirm your group's ideas, or did it cause you to rework your
arrangement of the fossil parts? Explain.
17. If this "Fossil Find" scenario is typical of the work of scientists, what features of the nature
of science does it demonstrate?
18. From looking at the fossil and the resource manual, what could you say about how and
where this animal lived?
19. Is it possible for scientists to do studies about things that happened millions of years ago?
Explain.
20. Below, or on the back of this sheet, list what you see as the 3 goals of this experience.
E
Evvoolluuttiioonn aanndd D
Diivveerrssiittyy
Using the six stations that are available for
match the term to the description:
Term
Description
1. Adaptive Radiation
a)
2. Analogous Structures
b)
3. Embryology
4. Geographic
c)
Separation
5. Homologous
d)
Structures
6. Mutations
e)
f)
this lesson, complete the three questions.
Then
Random changes in DNA
Changes in DNA prevent species from
interbreeding
How an organism develops matches
how its related to other organisms
Organisms change in response to their
environment
Same function, different structure
Same structure, different function
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Addaappttiivvee R
Raaddiiaattiioonn
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Galapagos finches are often called “Darwin's finches” because he was the first scientist to try and
explain why there were so many different kinds of finches on the Galapagos Islands. He
explained that the beaks of the finches were different because of adaptive radiation, when a
species of organism adapts to different environments.
1. How are the beaks of finches that eat mainly insects and mainly seeds different?
2. According to the diagram, all of these finches began as a type of finch that ate seeds.
Why would they start to eat things other than seeds?
3. Think of another example of adaptive radiation, using animals that you are more familiar
with.
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Annaallooggoouuss S
Sttrruuccttuurreess
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Why Do Animals Survive or Die?
This diagram shows the wing structure of four different animals: insect, dinosaur, bird and bat.
1. Differentiate in two ways the wings of the bird and the insect.
2. “Batman” is a fictional character, but humans are capable of flight with structures like
hang-gliders. Explain why, if he were real, “Batman” would have to have wings many
times bigger than they are in the movies.
3. Wings are examples of analogous structures because they have the same function, but
very different bone structures (and sometimes, no bones at all). Think of two animals
that have parts which do the same thing, but have very different structures. [Hint: Think
about how land animals get around.]
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Geeooggrraapphhiicc S
Seeppaarraattiioonn
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Evolution
The diagram shows how “greenish warbles” started in the Himalayas, but, over thousands of
years, migrated to Siberia by two different paths, one through China and one through
Kazakhstan. Due to changes in the warblers over those thousands of years, this geographic
separation made it impossible for the two types of warbles to breed with each other when they
met again in Siberia.
1. Can the populations in squares “A” and “B” interbreed? What about “A” and “F”? “D” and
“E”? Why?
2. What causes geographic separation to create different species?
3. How can you tell if two animals which look and seem very similar are in the same or in
different species?
M
Muuttaattiioonnss
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This diagram shows different strains of bacteria (the dots) and how resistant they are to
antibiotics. The strains of bacteria are different because of mutations (changes in DNA) that
cause differences in offspring.
1. According to the diagram, how many bacterial strains from the original population survive
when an antibiotic is used?
2. What is the difference between the original and final population of bacteria?
3. Antibiotics that kill bacteria are being developed all of the time. In terms of mutations,
why can't scientists just find an antibiotic that kills all bacteria all of the time?
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Em
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Evolution
When a sperm fertilizes an egg for any animal, the beginning of this new life looks very similar,
no matter what the animal. The above diagram shows the embryology for eight different
animals. Animals that are highly related show more similarities in their development from an
egg to a mature adult.
1. What do you notice that humans have during their development that, when born, we do
not have? Why is this?
2. What structures do you see that all the eight animals have in common in the final stage
(III)?
3. From looking at this embryology chart, describe the common ancestor of all of these
animals.
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Why Do Animals Survive or Die?
This diagram shows the arm, leg, flipper and wing of four mammals. All four mammals
eventually descend from a common mammal ancestor, and show similar bone structures. The
upper bone (that connects to the body of the animal) is called the humerus. The bones that
connect the humerus to the “fingers” are the radius and ulna. The radius is found on the
“thumb” side of the arm, the ulna on the little-finger side. (As an experiment, you can feel them
in your own arm by holding your forearm and twisting your wrist.) The carpals form the wrist
(or ankle) and the phalanges form the “fingers” or “toes.”
1. The phalanges of the whale and human are different. Why? Include in your response the
environments in which the two live.
2. Using the above diagram and your knowledge of animals, explain why the cat and bat
have different leg / wing structures.
3. These are called homologous structures because they have similar bones but different
functions. Think of two animals that have the same structure, but the animals use it for
different reasons.
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Natural selection is the chief mechanism of evolution. It is the process that gives rise to
populations that are adapted to their environments. Organisms with favorable variations tend to
survive and pass their variations to offspring while those with unfavorable variations are
eliminated. In this investigation your team, working with other teams in the class, will design
and conduct a simulation experiment to answer a question concerning the evolution of seed
coloration in pinto bean seeds.
1. What are the main features of natural selection?
It is important to a population of bean plants that its seeds survive and grow into a new
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Evolution
B
Beeaannss aanndd B
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generation of plants. Mutations may have produced many seed color variations such as red, blue,
brown, orange, and white. Since the seed colors that actually exist in pinto bean plants are
brown and white, it seems reasonable to conclude that these colors are an advantage to the
bean plants' survival and were selected over many generations. The problem you will investigate
using pinto bean seeds is: "How does natural selection change the frequency of genes or traits in
a population over many generations?"
2. Get the following materials:
a) One container each of red, blue, brown, white, and orange pinto bean seeds
b) Four meter sticks
c) Habitat such as the school lawn
d) Graph paper
3. Using the materials on the above list, design an experiment that answers the question
posed by the problem:"How does natural selection change the frequency of genes or traits
over many generations?" In designing your investigation:
a) State a hypothesis
b) Describe a procedure
c) Determine what data to collect
4. Share your team design with other teams in the class and select a common class
hypothesis, procedure, and data table.
5. Do the experiment and record the data.
6. Make a graph to illustrate your data.
7. Study your survivor populations for each generation. What changes occurred in the
frequencies of colors between each generation?
8. Compare the original and survivor populations. Is there any seed color or colors from the
original population that are not represented in the survivor population?
9. How do the colors of the survivors relate to their habitat?
10. What do you predict would happen to the frequencies of colors if you continued the
simulation activity for several more generations?
11. How might new mutations for additional seed colors affect the frequencies of genes for
color in the population?
12. How might the population change if pinto bean plants migrated into or out of the
population?
13. How might a change in the habitat or in the animals (herbivores) eating the seeds affect
the frequencies of seed colors?
14. Have you confirmed your hypothesis? Explain.
15. Explain how natural selection changes the frequency of genes over many generations.
16. How would you improve this experiment? Comment on seed color, habitat, seed eating
herbivores, number of repetitions, season of the year, etc.
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Who Came Up With Evolution?
Who Came Up With Evolution?
Describe historical scientific developments that happened in evolutionary thought.
Lamarck and Darwin and Mendelian Genetics.
For example,
True or False?
YOU do NOT necessarily have to AGREE with the statement for it to be "true" as you think
biologists see it. For each one, write down whether it is true or false!
17. Evolution is a scientific fact. T / F
18. Evolution is something you should either believe in, or not believe in. T / F
19. Evolution is a process that involved the origin of life. T / F
20. Evolution is primarily concerned with the origin of humans. T / F
21. According to evolution, people came from monkeys a long time ago. T / F
22. Evolution is something that happened only in the past; it is not happening now. T
/F
23. Evolution is something that happens to individual organisms. T / F
24. Evolution is a totally random process, or a series of "accidents". T / F
25. Evolution tells us that there is no God. T / F
26. Evolution simply means "change". T / F
27. There is actually very little evidence for evolution. T / F
28. Evolution theory has been tested many times, and has always been supported by
the evidence. T / F
29. Dinosaurs lived during the time of early humans. T / F
30. Evolution involves individuals changing in order to adapt to their environment. T /
F
31. The formation of complex structures, like the eye, can be readily explained by
evolution. T / F
About the History of Evolution
Once scientists started noticing that the best organisms were surviving and the weak were
dying, they called this natural selection. This part was clear to all scientists, as natural selection
happened in all parts of their daily lives. What scientists did not initially agree upon, though, was
how organisms got more advantageous characteristics.
There is now a lot of evidence for the type
of evolution that Charles Darwin (see article) first
proposed. It is not a fact that evolution happens
this way, as the theory is always changing very
slightly. Unlike natural selection, evolution is
actually a fairly complicated theory that takes
some time to truly understand. However,
evolution takes into account all of the current
evidence that scientists have uncovered.
Evolution basically means that
populations of organisms gain more advantageous
characteristics (for their environment) over time.
Evolution does not happen to individual organisms
and is not random – it is not a series of accidents.
It is also not a series of events to get to some
end animal. Evolution happens for a reason: the
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Evolution
changes in the population help the organisms survive better. Since there can be millions of
different possible changes, there is no “correct” change that has to happen. Nobody can predict
how evolution will change bacteria, mice or even humans over the next million years.
Evolution is not just a theory about humans, it's about all living things. Evolution is also not
a system of beliefs! Evolution just happens to be the best explanation for what scientists can
observe about the world. Therefore, evolution says nothing about the presence or absence of God,
or about what you should or should not believe.
There are many misconceptions about evolution. Scientists do not think that humans
evolved from monkeys; rather, humans and monkeys are thought to have a common ancestor
some many millions of years ago. This ancestor was not necessarily like today's monkeys and also
not exactly like a human. But because evolution means that organisms are constantly improving
themselves over time, this ancestor of ours does not exist any more because some of their
offspring evolved into monkeys and some into humans.
Another misconception about evolution is that humans and dinosaurs lived at the same
time. Well, it is true that ancient ancestors of humans, about the size and shape of a large mouse,
lived at the same time as dinosaurs. However, it took millions of years after dinosaurs went extinct
for most of the mammals that are around today to evolve, including humans!
True or False?
YOU do NOT necessarily have to AGREE with the statement for it to be "true" as you think
biologists see it. For each one, write down whether it is true or false!
32. Evolution is a scientific fact. T / F
33. Evolution is something you should either believe in, or not believe in. T / F
34. Evolution is a process that involved the origin of life. T / F
35. Evolution is primarily concerned with the origin of humans. T / F
36. According to evolution, people came from monkeys a long time ago. T / F
37. Evolution is something that happened only in the past; it is not happening now. T
/F
38. Evolution is something that happens to individual organisms. T / F
39. Evolution is a totally random process, or a series of "accidents". T / F
40. Evolution tells us that there is no God. T / F
41. Evolution simply means "change". T / F
42. There is actually very little evidence for evolution. T / F
43. Evolution theory has been tested many times, and has always been supported by
the evidence. T / F
44. Dinosaurs lived during the time of early humans. T / F
45. Evolution involves individuals changing in order to adapt to their environment. T /
F
46. The formation of complex structures, like the eye, can be readily explained by
evolution. T / F
Questions
Do you remember?
1. Complete this phrase in your own words: Evolution means that
_________________________________________________________________________
2. Did humans evolve from monkeys? Explain!
3. Is evolution happening right now?
Think about it!
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Who Came Up With Evolution?
4. Is there such a thing as scientific fact? Why or why not?
5. Infer what would have happened if the common ancestor between monkeys and humans had
never been able to reach the ground. Come up with at least two points.
Do something!
6. Think about the small mammal that was described at the end of the reading. After the
dinosaurs went extinct, how do you think this population of mouse-like mammals started to
evolve? Come up with three different populations that you feel must have evolved from this
one mouse-like population. Describe each one in one paragraph and make a quick sketch.
Remember?
7. Compare and contrast a conclusion and a theory.
8. Explain why science doesn't have firm answers to questions.
9. Explain why the amount of oxygen in the atmosphere increased soon after the Earth was
formed.
10. Define natural selection in your own words.
Lamarck vs. Darwin
Jean-Baptiste Lamarck (1744-1829) and Charles Darwin (1809-1882) both thought and had ideas
about how life on earth got to be the way it is now. They had some similar and some very different
ideas.
How They Agreed
Unlike most other people at that time, Darwin and Lamarck both thought that life had
changed gradually over time and was still changing, that living things change to be better suited
and adapted to their environments, and that all organisms are related. Darwin and Lamarck also
agreed that life evolved from fewer, simpler organisms to many, more complex organisms.
What Lamarck Thought
Lamarck is best known for his Theory of Inheritance of Acquired Characteristics, first
presented in 1801 (Darwin's first book dealing
with natural selection was published in 1859): If
an organism changes during life in order to adapt
to its environment, those changes are passed on
to its offspring. He said that change is made by
what the organisms want or need. For example,
Lamarck thought that elephants all used to have
short trunks. When there was no food or water
that they could reach with their short trunks,
they stretched their trunks to reach the water
and branches, and their offspring inherited long
trunks. Lamarck also said that body parts that
are not being used, such as the human appendix
and little toes are gradually disappearing. Eventually, people will be born without these parts.
Lamarck also thought that evolution happens according to a predetermined plan and that the
results have already been decided.
What Darwin Thought
Darwin thought that the desires of animals have nothing to do with how they evolve, and
that changes in an organism during its life do not affect the evolution of the species. He said that
organisms, even of the same species, are all different and that those which happen to have
variations that help them to survive in their environments survive and have more offspring. The
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offspring are born with their parents' helpful traits, and as they reproduce, individuals with that
trait make up more of the population. Other individuals, that are not so well adapted, die off. Most
elephants used to have short trunks, but some had longer trunks. When there was no food or
water that they could reach with their short trunks, the ones with short trunks died off, and the
ones with long trunks survived and reproduced. Eventually, all of the elephants had long trunks.
Darwin also thought that evolution does not happen according to any sort of plan.
Why We Agree With Darwin
Darwin's theory has been supported by a lot of evidence. Lamarck's Theory of Inheritance of
Acquired Characteristics has been disproved. This was done in two major ways. The first is by
experiment. We have seen through many real examples and observations that changes that occur
in an animal during life are not passed on to the animal's offspring. If a dog's ears are cropped
short, its puppies are still born with long ears. If someone exercises every day, runs marathons,
eats well, and is generally very healthy, the fitness is not passed on and the person's children still
have to work just as hard to get that fit and healthy. These and other examples show that
Lamarck's theory does not explain how life formed and became the way it is.
The other way that Lamarck's theory has been proven wrong is the study of genetics.
Darwin knew that traits are passed on, but he never understood how they are passed on. During
the time when Darwin's first book first came out, Gregor Mendel, who discovered genetics, was just
starting his experiments. However, now we know a lot more about genetics, and we know that the
only way for traits to be passed on is through genes, and that genes can not be affected by the
outside world. The only thing that can be affected is which gene sets there are in a population, and
this is determined by which individuals die and which ones live. This is the other way that we have
learned that the fruits of an animal's efforts can not be inherited by its offspring.
Respond
1.
2.
3.
4.
What did Darwin think?
What did Lamarck think?
Who was more correct? Why?
If evidence came along suggesting that evolution was wrong, what would scientists do?
FAQ about Evolution
What is evolution?
Biological evolution refers to the cumulative changes that occur in a population over time.
These changes are produced at the genetic level as organisms' genes mutate and/or recombine in
different ways during reproduction and are passed on to future generations. Sometimes, individuals
inherit new characteristics that give them a survival and reproductive advantage in their local
environments; these characteristics tend to increase in frequency in the population, while those
that are disadvantageous decrease in frequency. This process of differential survival and
reproduction is known as natural selection. Non-genetic changes that occur during an organism's
life span, such as increases in muscle mass due to exercise and diet, cannot be passed on to the
next generation and are not examples of evolution.
Isn't evolution just a theory that remains unproven?
In science, a theory is a rigorously tested statement of general principles that explains
observable and recorded aspects of the world. A scientific theory therefore describes a higher level
of understanding that ties "facts" together. A scientific theory stands until proven wrong -- it is
never proven correct. The Darwinian theory of evolution has withstood the test of time and
thousands of scientific experiments; nothing has disproved it since Darwin first proposed it more
than 150 years ago. Indeed, many scientific advances, in a range of scientific disciplines including
physics, geology, chemistry, and molecular biology, have supported, refined, and expanded
evolutionary theory far beyond anything Darwin could have imagined.
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Are all species related?
Yes. Just as the tree of life illustrates, all organisms, both living and extinct, are related.
Every branch of the tree represents a species, and every fork separating one species from another
represents the common ancestor shared by these species. While the tree's countless forks and farreaching branches clearly show that relatedness among species varies greatly, it is also easy to see
that every pair of species share a common ancestor from some point in evolutionary history. For
example, scientists estimate that the common ancestor shared by humans and chimpanzees lived
some 5 to 8 million years ago. Humans and bacteria obviously share a much more distant common
ancestor, but our relationship to these single-celled organisms is no less real. Indeed, DNA analyses
show that although humans share far more genetic material with our fellow primates than we do
with single-celled organisms, we still have more than 200 genes in common with bacteria.
It is important to realize that describing organisms as relatives does not mean that one of
those organisms is an ancestor of the other, or, for that matter, that any living species is the
ancestor of any other living species. A person may be related to blood relatives, such as cousins,
aunts, and uncles, because she shares with them one or more common ancestors, such as a
grandparent, or great-grandparent. But those cousins, aunts, and uncles are not her ancestors. In
the same way, humans and other living primates are related, but none of these living relatives is a
human ancestor.
What is a species?
Members of one species do not normally interbreed with members of other species in
nature. Sometimes, members of different species, such as lions and tigers, can interbreed if kept
together in captivity. But in nature, geographic isolation and differences in behavior, such as choice
of habitat, keep these sorts of closely related animal species apart. Similarly, closely related
species of plants can sometimes be hybridized by horticulturists, but these hybrids are rarely found
in nature. A species, then, is defined by science as a group of interbreeding or potentially
interbreeding populations that is reproductively isolated from other such groups.
What do genes have to do with evolution?
Genes are the portions of an organism's DNA that carry the code responsible for building
that organism in a very specific way. Genes -- and, thus, the traits they code for -- are passed from
parent to offspring. From generation to generation, well-understood molecular mechanisms
reshuffle, duplicate, and alter genes in a way that produces genetic variation. This variation is the
raw material for evolution.
What role does sex play in evolution?
Sexual reproduction allows an organism to combine half of its genes with half of another
individual's genes, which means new combinations of genes are produced every generation. In
addition, when eggs and sperm are produced, genetic material is shuffled and recombined in ways
that produce new combinations of genes. Sexual reproduction thus increases genetic variation,
which increases the raw material on which natural selection operates. Genetic variation within a
species -- also known as genetic diversity -- increases a species' opportunity for change over
successive generations.
Is evolution a random process?
Evolution is not a random process. The genetic variation on which natural selection acts may
occur randomly, but natural selection itself is not random at all. The survival and reproductive
success of an individual is directly related to the ways its inherited traits function in the context of
its local environment. Whether or not an individual survives and reproduces depends on whether it
has genes that produce traits that are well adapted to its environment.
Are evolution and "survival of the fittest" the same thing?
Evolution and "survival of the fittest" are not the same thing. Evolution refers to the
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cumulative changes in a population or species through time. "Survival of the fittest" is a popular
term that refers to the process of natural selection, a mechanism that drives evolutionary change.
Natural selection works by giving individuals who are better adapted to a given set of
environmental conditions an advantage over those that are not as well adapted. Survival of the
fittest usually makes one think of the biggest, strongest, or smartest individuals being the winners,
but in a biological sense, evolutionary fitness refers to the ability to survive and reproduce in a
particular environment. Popular interpretations of "survival of the fittest" typically ignore the
importance of both reproduction and cooperation. To survive but not pass on one's genes to the
next generation is to be biologically unfit. And many organisms are the "fittest" because they
cooperate with other organisms, rather than competing with them.
How does natural selection work?
In the process of natural selection, individuals in a population who are well-adapted to a
particular set of environmental conditions have an advantage over those who are not so well
adapted. The advantage comes in the form of survival and reproductive success. For example,
those individuals who are better able to find and use a food resource will, on average, live longer
and produce more offspring than those who are less successful at finding food. Inherited traits that
increase individuals' fitness are then passed to their offspring, thus giving the offspring the same
advantages.
How do organisms evolve?
Individual organisms don't evolve. Populations evolve. Because individuals in a population
vary, some in the population are better able to survive and reproduce given a particular set of
environmental conditions. These individuals generally survive and produce more offspring, thus
passing their advantageous traits on to the next generation. Over time, the population changes.
Does evolution prove there is no God?
No. Many people, from evolutionary biologists to important religious figures like Pope John
Paul II, contend that the time-tested theory of evolution does not refute the presence of God. They
acknowledge that evolution is the description of a process that governs the development of life on
Earth. Like other scientific theories, including Copernican theory, atomic theory, and the germ
theory of disease, evolution deals only with objects, events, and processes in the material world.
Science has nothing to say one way or the other about the existence of God or about people's
spiritual beliefs.
Did we evolve from monkeys?
Humans did not evolve from monkeys. Humans are more closely related to modern apes
than to monkeys, but we didn't evolve from apes, either. Humans share a common ancestor with
modern African apes, like gorillas and chimpanzees. Scientists believe this common ancestor
existed 5 to 8 million years ago. Shortly thereafter, the species diverged into two separate lineages.
One of these lineages ultimately evolved into gorillas and chimps, and the other evolved into early
human ancestors called hominids.
How did humans evolve?
Since the earliest hominid species diverged from the ancestor we share with modern African
apes, 5 to 8 million years ago, there have been at least a dozen different species of these
humanlike creatures. Many of these hominid species are close relatives, but not human ancestors.
Most went extinct without giving rise to other species. Some of the extinct hominids known today,
however, are almost certainly direct ancestors of Homo sapiens. While the total number of species
that existed and the relationships among them is still unknown, the picture becomes clearer as new
fossils are found. Humans evolved through the same biological processes that govern the evolution
of all life on Earth. See "What is evolution?", "How does natural selection work?", and "How do
organisms evolve?"
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Who Came Up With Evolution?
Is culture the result of evolution?
A society's culture consists of its accumulated learned behavior. Human culture is based at
least partly on social living and language, although the ability of a species to invent and use
language and engage in complex social behaviors has a biological basis. Some scientists
hypothesize that language developed as a means of establishing lasting social relationships. Even a
form of communication as casual as gossip provides an ingenious social tool: Suddenly, we become
aware of crucial information that we never would have known otherwise. We know who needs a
favor; who's available; who's already taken; and who's looking for someone -- information that,
from an evolutionary perspective, can mean the difference between failure and success. So, it is
certainly possible that evolutionary forces have influenced the development of human capacities for
social interaction and the development of culture. While scientists tend to agree about the general
role of evolution in culture, there is still great disagreement about its specific contributions.
How are modern humans and Neanderthals related?
There is great debate about how we are related to Neanderthals, close hominid relatives
who coexisted with our species from more than 100,000 years ago to about 28,000 years ago.
Some data suggest that when anatomically modern humans dispersed into areas beyond Africa,
they did so in small bands, across many different regions. As they did so, according to this
hypothesis, humans merged with and interbred with Neanderthals, meaning that there is a little
Neanderthal in all modern Europeans.
Scientific opinion based on other sets of data, however, suggests that the movement of
anatomically modern humans out of Africa happened on a larger scale. These movements by the
much more culturally and technologically advanced modern humans, the hypothesis states, would
have been difficult for the Neanderthals to accommodate; the modern humans would have outcompeted the Neanderthals for resources and driven them to extinction.
What do humans have in common with single-celled organisms?
Evolution describes the change over time of all living things from a single common ancestor.
The "tree of life" illustrates this concept. Every branch represents a species, each connected to
other such branches and the rest of tree as a whole. The forks separating one species from another
represent the common ancestors shared by these species. In the case of the relatedness of
humans and single-celled organisms, a journey along two different paths -- one starting at the tip
of the human branch, the other starting at the tip of a single-celled organism's branch -- would
ultimately lead to a fork near the base of the tree: the common ancestor shared by these two very
different types of organisms. This journey would cross countless other forks and branches along
the way and span perhaps more than a billion years of evolution, but it demonstrates that even the
most disparate creatures are related to one another -- that all life is interconnected.
What happened in the Cambrian explosion?
Life began more than 3 billion years before the Cambrian, and gradually diversified into a
wide variety of single-celled organisms. Toward the end of the Precambrian, about 570 million
years ago, a number of multicelled forms began to appear in the fossil record, including
invertebrates resembling sponges and jellyfish, and some as-yet-unknown burrowing forms of life.
As the Cambrian began, most of the basic body plans of invertebrates emerged from these
Precambrian forms. They emerged relatively rapidly, in the geological sense -- over 10 million to 25
million years. These Cambrian forms were not identical to modern invertebrates, but were their
early ancestors. Major groups of living organisms, such as fish, amphibians, reptiles, birds, and
mammals, did not appear until millions of years after the end of the Cambrian Period.
Why do some species survive while others go extinct?
Extinction is often caused by a change in environmental conditions. When conditions
change, some species possess adaptations that allow them to survive and reproduce, while others
do not. If the environment changes slowly enough, species will sometimes evolve the necessary
adaptations, over many generations. If conditions change more quickly than a species can evolve,
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however, and if members of that species lack the traits they need to survive in the new
environment, the likely result will be extinction.
Does evolution proceed toward increasing complexity?
In the approximately 3.8 billion years since life originated on Earth, evolution has resulted in
many complex organisms and structures. The human brain and stereoscopic eyes are just two
examples. At the same time, simpler organisms like algae, bacteria, yeast, and fungi, which arose
several billion years ago, not only persist but thrive. The presence of single-celled organisms
alongside complex organisms like humans testifies to the fact that evolution within a given lineage
does not necessarily advance toward increasing complexity. When more complex organs are
advantageous, complex organs have arisen. Single-celled organisms, however, fill many roles, or
niches, much better than any multicellular organism could, and so they remain in a relatively stable
state of adaptation.
If fish became amphibians through the process of evolution, then why do
fish still exist?
Fossil evidence clearly shows that amphibians descended from one group of ancient fishes
whose thick, bony fins gradually evolved into limb-like appendages. Other species gave rise to the
kinds of fish that inhabit oceans, lakes, and streams around the world today. Fish, like all living
creatures, continue to evolve. This evolution is not toward a life on land, but instead toward
successful use of the underwater environment. There are countless ecological opportunities under
water, which is why fish still exist. When the earliest ancestors of modern amphibians left the
water, they found many new opportunities on land. As amphibians and other land creatures
diversified, however, fewer and fewer opportunities existed for newcomers.
Could apes ever evolve into some other humanlike creature?
It is possible that in many millions of years present day apes could evolve into some other
humanlike species. It is, however, very improbable. First of all, humans did not evolve from any of
the species we know as apes today. At some point 5 to 8 million years ago, the common ancestor
of humans and modern apes diverged to form the two separate lineages we know today. The
species at the end of these lineages are a result of a very specific combination of selection
pressures and genetic mutations over millions of years. This same combination is highly unlikely to
occur ever again.
Are humans influencing the process of evolution?
Most scientists would agree unequivocally that humans have greatly affected the process of
evolution, from the rise of antibiotic and pesticide resistance to the largely human-caused increase
in the extinction rate. Our effect on the process of evolution even extends to our own species'
evolution. Technology and culture have protected us to a great extent from the selective pressures
that drive evolution, allowing many people -- especially those in developed nations who, without
medical intervention, would not live to reproductive age -- to pass their genes on to the next
generation. Other scientists note that technology and culture have changed but not eliminated the
role of natural selection on our species. We now adapt to crowding, pollution, and new disease
rather than the necessity to escape from large predators. Humans will change in the future, but are
unlikely to evolve into a new, separate species because no human group is truly isolated anymore,
given our transportation systems. Without genetic isolation, there is no further opportunity for
speciation among humans.
If humans evolved from apes then why are there still apes?
Humans did not evolve from present-day apes. Rather, humans and apes share a common
ancestor that gave rise to both. This common ancestor, although not identical to modern apes, was
almost certainly more apelike than humanlike in appearance and behavior. At some point -scientists estimate that between 5 and 8 million years ago -- this species diverged into two distinct
lineages, one of which were the hominids, or humanlike species, and the other ultimately evolved
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into the African great ape species living today.
Is there evidence for evolution?
In the 150 years since Darwin proposed the theory of evolution by natural selection, a
mountain of evidence has accumulated to support the theory. A greatly expanded fossil record
since Darwin's time, the discovery of DNA and the process of genetic replication, an understanding
of radioactive decay, observations of natural selection in the wild and in laboratories, and evidence
in the genomes of many different organisms, including humans, have all bolstered the validity of
the theory of evolution.
How can you know what happened millions of years ago if no one was
there to see it?
Evidence and observation are the building blocks of all scientific inquiry; evolutionary
science is no different. Evidence in the form of the fossil record, geological formations, and genetics
attest to change having taken place and give clues to how evolution works. The theory of evolution
puts these clues together into a cohesive explanation of the diversity of living things. Like all
theories, the theory of evolution relies on tangible evidence as well as inference for those things
that can't be observed directly. It is important to remember that Earth itself contains evidence of
life in the past, and that this evidence provides critical support for the theory of evolution.
Does the fossil record tell us the whole story?
Opponents of evolution point to gaps in the fossil record as proof that the theory is invalid.
They say the fossil record fails to show what are called "transitional forms," generally the inbetween stages as one type of creature evolved into another. The fossil record certainly has gaps,
mostly because the conditions required to create fossils have been rare ever since life began on
Earth. A very small percentage of animals that have lived and died ever became fossils. Thus,
many pieces of the puzzle are missing; some will never be found. Nonetheless, we have many,
many fossils that illustrate evolutionary transitions between fish and amphibians, between reptiles
and mammals, between dinosaurs and birds, and in many lineages such as whales and horses. And
new fossils continue to reveal transitional forms that some said don't exist.
How can one species "turn into" another?
One species does not "turn into" another or several other species -- not in an instant,
anyway. The evolutionary process of speciation is how one population of a species changes over
time to the point where that population is distinct and can no longer interbreed with the "parent"
population. In order for one population to diverge enough from another to become a new species,
there needs to be something to keep the populations from mixing. Often a physical boundary
divides the species into two (or more) populations and keeps them from interbreeding. If separated
for long enough and presented with sufficiently varied environmental conditions, each population
takes its own distinct evolutionary path. Sometimes the division between the populations is never
breached, and reproductive isolation remains intact purely for geographical reasons. It is possible,
though, if the populations have been separate for long enough, that even if brought back together
and given the opportunity to interbreed they won't, or they won't be successful if they try.
How can evolution produce complex organs like the eye?
In the process of natural selection, individuals in a population who are well-adapted to a
particular set of environmental conditions have an advantage over those who are not so well
adapted. These individuals pass their genes and advantageous traits to their offspring, giving the
offspring the same advantages. Generation after generation, natural selection acts upon each
structure within an organ like the eye, producing incremental improvements in the process. Each
tiny change in a structure is dependent upon changes in all the other structures. In this way,
individual parts of a system evolve in unison to be both structurally and functionally compatible.
Eventually, over thousands and sometimes millions of years, the small improvements add up -- the
simple, systematic process has produced an almost unfathomably complex organ. Recently,
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scientists have found clues to the evolutionary pasts of some of the most complex organs, helping
to clarify how this process works.
Does evolution stop once a species has become a species?
Evolution does not stop once a species becomes a species. Every population of living
organisms is undergoing some sort of evolution, though the degree and speed of the process varies
greatly from one group to another. Populations that experience a major change in environmental
conditions, whether that change comes in the form of a new predator or a new island to disperse
to, evolve much more quickly than do populations in a more stable set of conditions. This is
because evolution is driven by natural selection, and because when the environment changes,
selective pressures change, favoring one portion of the population more heavily than it was favored
before the change.
Is evolution happening now?
Evolution is always happening, though often at rates far too slow to be observed in a matter
of days, weeks, or even years. The effects of evolution can be felt in almost every aspect of our
daily lives, though, from medical and agricultural dilemmas to the process of choosing a good
mate. In medicine, there's the question of how long the antibiotics we take now will remain
effective, given the relatively fast rate at which bacteria can evolve resistance to drugs. In
agriculture, the need to protect this year's crops is pitted against the concern that doing so will set
the stage for insects to evolve pesticide resistance. For all of us, there is the issue of decreasing
biodiversity, as most scientists believe that life on Earth is currently undergoing a mass extinction
in which 50 percent or more of species will die out. These are just a few examples of ways in which
evolutionary processes affect our daily lives.
How long does evolution take?
Even though evolution is taking place all around us, for many species the process operates
so slowly that it is not observable except over thousands or hundreds of thousands of years -much too long to witness in a human lifetime. There are cases in quickly reproducing life forms like
bacteria and fruit flies, however, where evolution can be seen happening in a matter of weeks for
the bacteria and many months for the flies. In these cases the relatively large number of
generations in a given period of time is key, since evolutionary change occurs incrementally from
one generation to the next. All else being equal, the more generations you have, the more quickly
evolution happens.
Can you observe evolution happening?
Because for many species, humans included, evolution happens over the course of many
thousands of years, it is rare to observe the process in a human lifetime. Usually only laboratory
scientists studying quickly reproducing life forms, like single-celled creatures and some
invertebrates, have the opportunity to see evolutionary change happen before their eyes. All of us
can and do experience the indirect effects of evolution nearly every day, however. One of the more
important evolutionary concerns facing humans today is the emergence of antibiotic-resistant
microbes. A battle against bacteria that we have been winning with medicine for the last 50 years
or so is now an even race, according to some scientists -- because of the rapid rate of bacterial
evolution. Similarly, the use of pesticides in agriculture has driven the evolution of resistant insects
that require more or harsher chemicals to be killed. Scientists studying Galapagos finches have
seen evolutionary changes in beak size and shape in just a few years. Major evolutionary
transformations take much, much longer.
How long ago did dinosaurs exist?
Dinosaurs existed between 230 million years ago and 65 million years ago, but none of the
known dinosaur species existed for this entire time period. Throughout the group's existence,
individual dinosaur species were evolving and going extinct. Some species diverged and gave rise
to other species, while others disappeared. A mass extinction event at the end of the Cretaceous
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period, 65 million years ago, ended the reign of dinosaurs on Earth. Recently, many scientists have
come to the conclusion that, while dinosaurs may have disappeared, one dinosaur lineage had
evolved into birds long before the extinction event that wiped out the other dinosaurs -- and so, in
a sense, dinosaurs are still around today.
How long ago did humans become human?
The oldest known hominid, or humanlike species, has been dated at 4.4 million years old.
Another species, which is yet to be confirmed as a hominid, has been dated at 6 million years old.
Scientists estimate that the hominid lineage diverged from the ape lineage 5 to 8 million years
ago. Homo sapiens, the species to which we belong, has existed for about 100,000 years.
Who was Charles Darwin?
Charles Darwin was born on February 12, 1809, in Shrewsbury, England. His father, Robert
Darwin, was a physician, the son of Erasmus Darwin, a poet, philosopher, and naturalist. Charles's
mother,
Susannah
Wedgwood
Darwin,
died
when
he
was
eight
years
old.
At age 16, Darwin left Shrewsbury to study medicine at Edinburgh University. He later enrolled in
Cambridge University to prepare for a career as a clergyman in the Church of England. After
receiving his degrees in 1831, Darwin accepted an invitation to serve as an unpaid naturalist on a
five-year scientific expedition to South America aboard the HMS Beagle. This voyage and Darwin's
later research formed the basis for his theory of evolution by means of natural selection, detailed in
his book “On the Origin of Species”, published in 1859.
Darwin continued throughout most of the rest of his life to publish his research and writings
on biology. In his later years, Darwin was plagued by fatigue and intestinal sickness, thought by
some historians to have been caused by Chagas' disease, contracted during his travels in South
America. He died on April 19, 1882, and lies buried in Westminster Abbey.
Why was Darwin's idea considered dangerous?
Darwin's theory of evolution by natural selection was considered dangerous in 19th-century
England because it threatened the prevailing views of the Anglican Church and society at large. If
extrapolated beyond its role as a scientific theory, it seemed to run counter to the notion of
humankind's supremacy and God's hand in the world order. The same fear exists today. Evolution
can seem to be in direct conflict with deeply held belief systems of how life came to exist on Earth.
How can the evolution of one species affect the evolution of another?
No species exists in a vacuum; every form of life on Earth interacts over time with other
organisms, as well as with its physical environment. For that reason, the evolution of one species
influences the evolution of species with which it coexists by changing the natural selection
pressures those species face. The classic examples of this sort of evolution, called coevolution, are
predator-prey and host-parasite relationships.
One such predator-prey relationship exists between garter snakes and a species of
salamander-like amphibian called a rough-skinned newt. In parts of the midwestern United States,
garter snakes prey on newts, and probably have for thousands of years. In that time, over
countless generations, the newts have evolved a powerful defense: a toxic chemical that they
secrete through their skin. Where garter snakes are concerned, however, this defense mechanism
has only been marginally successful. Generation after generation, as the newts became more
poisonous, the snakes also evolved, developing greater tolerance to the newt's toxin. The result of
this coevolutionary process, played out over countless snake and newt generations, is a chemical
more toxic than almost any other natural substance on Earth, and a population of snakes that are
seemingly immune to the toxin's effects.
What does it mean when some scientists say humans have stopped
evolving?
Technology and culture have protected us to a great extent from the selective pressures that
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drive evolution, allowing many people, especially those in developed nations who would otherwise
not live to reproductive age, to pass their genes on to the next generation. In addition, human
groups are no longer isolated; they travel the globe. Without genetic isolation, there is no further
opportunity for speciation among humans. On the other hand, natural selection is a function of
environmental change, and our physical, biological, and cultural environments have changed
tremendously. Humans face, for example, new diseases like HIV/AIDS that can greatly impact
survival and reproduction. Human populations may also be undergoing evolutionary changes of
which we're not yet aware.
If extinction is a natural part of life on Earth, why should we care about
protecting endangered species?
If the mass extinction most scientists agree we're experiencing now is allowed to continue,
it will be the first time in the history of life on Earth that a single species would be responsible for
such a catastrophe. And although extinction is a natural process that has occurred many times in
the distant past, it's a process that would be in our best interest to avoid. The extinction of just one
species can dramatically impact many others, and like all creatures, humans rely heavily on other
species. It is therefore impossible to predict how we might ultimately be affected by a mass
extinction.
How does evolution affect me in my daily life?
We can and do experience the indirect effects of evolution nearly every day. One of the
more important evolutionary concerns facing humans today is the continual evolution of antibioticresistance in bacteria. The successful medical battle we have waged against bacteria for the last 50
years is now an even race, according to some scientists. Similarly, the use of pesticides in
agriculture has driven the evolution of resistant insects, requiring the use of harsher chemicals in
greater quantity to kill them.
What is "intelligent design," and is it science?
"Intelligent design theory" is built on the belief that evolution does not sufficiently explain
the complexity that exists in life on Earth and that science should recognize the existence of an
"intelligent designer." Proponents assert that their criticism of evolution is scientific, not religious.
But the various aspects of intelligent design theory have not yet been subjected to the normal
process of scientific experimentation and debate, nor have they been accepted by the scientific
community. No research supporting the claims of intelligent design has ever been published in any
recognized, professional, peer-reviewed scientific journal. Finally, the question of whether there is
an intelligent designer is untestable using the methods of science, and therefore is not a scientific
claim.
What is "creation science"? Is it a real science?
Proponents of "creation science" hold that special creationism -- the conviction that God
created the universe, including humans and other living things, at one time in the relatively recent
past -- can be supported using the methods and theory of science. Scientists from many fields
have examined these ideas, however, and have found them to be scientifically insupportable. For
example, evidence for a very young Earth is incompatible with many different methods of
establishing the age of fossils and geological formations. Furthermore, because the basic proposals
of creation science are not subject to test and falsification, these ideas do not meet the criteria for
science.
Wouldn't it be fair to teach evolution and "creation science" and/or
"intelligent design" in public schools?
The Federal courts have ruled that creation science is not science at all, but a religious
concept. Therefore it is not appropriate content for a science classroom. More to the point,
evolution studies, like other sciences, are founded on a growing body of observable, reproducible
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Who Came Up With Evolution?
evidence in the natural world, whereas "creation science" is based on accounts written in the Bible
and "intelligent design" is not yet supported by scientific evidence. Teaching evolution alongside
these other approaches would imply that creation science and intelligent design theory are as
rigorously tested as evolution, and they are not.
Activities
B
Beeeettlleess,, P
Paarrtt 11
This is an introduction to evolution and an activity that you can do with other people. You will
take a single piece of paper and fold it in half four times and then cut along all of the folds. You
should now have sixteen pieces of paper. On each of those pieces of paper, you will draw a
beetle. Each beetle should have the following features:
7. A body
8. Antennae, either short or long
9. Four legs, either short or long
10.
Eyes, either small or big
11.
Beak (mouth), either small or big
Try your best to make each beetle different; this means that if one beetle has short antennae,
short legs, small eyes and a small beak, then your next beetle might have short antennae, short
legs, small eyes and a big beak.
The next step is where you will need another person. Ask the person to come up with an
imaginary environment for your beetles and ask them the following questions:
1. Do the beetles need to feel things that are very tall?
2. Do the beetles need to be able to run very quickly?
3. Do the beetles need to see things from far away?
4. Do the beetles need to eat things that are very big?
Given this environment, decide which four of your sixteen beetles are best suited for their
environment. You will turn in your beetles, a description of the imaginary environment according
to your friend, and a paragraph (at least 5 sentences) that explains why those four beetles are
best suited for the environment. Also, make a chart of your choice showing the results for one of
the characteristics of the beetles.
Keep in mind that you will use your beetles for the next homework assignment!
E
Evvoolluuttiioonn:: W
Whhaatt D
Doo Y
Yoouu TThhiinnkk??
1. Ask family and friends for at least three questions that they have about evolution. For
each question, write down exactly what question they asked.
2. Look at the FAQ about Evolution on page 18. In addition to the three questions you got
from friends and family, look up the answers to two more questions that you would like to
know the answers to.
3. Using each of the answers you got in #2, explain in your own words what you could tell
other people in order to fully answer the question.
G
Grraapphhiinngg O
Oppiinniioonnss
1. Using the class' responses from the 15 true/false questions at the beginning of this
chapter, create a tally of how many people got the right answer for each question.
2. Calculate the percentage of students who were correct for each question and place that
number next to the tally.
3. Create a line or bar graph that represents the percentages that you just calculated.
4. Which question(s) were most correctly responded? Why?
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Evolution
5. Which question(s) were least correctly responded? Why?
N
Naattuurree''ss P
Phhaarrm
maaccyy
This lab activity will offer a chance for you to get to know the many naturally found antibacterial
substances... sitting right on your kitchen shelves.
1. Form groups of 3 – 4. Assign an equipment manager, scribe and leader. If there's a
fourth person, then they should be the official reader.
2. You will be preparing an agar plate with four spices from the spice options offered by your
teacher. Choose the four that you want to test.
3. What is a zone of inhibition? Why is it important to the results of this experiment?
4. Put on your safety equipment. Divide the agar plate in four quadrants (on the bottom)
with the marker. Label the top of the agar plate with the spices that you have chosen.
5. Inoculate your plate with the liquid bacteria, according to the teacher's instructions.
6. Apply the chosen spices to the quadrants on the agar plate. Close up the plate so that
the top and bottom line up. Leave them in a safe place, at room temperature for three
days.
7. Write down your hypothesis about what you think you will see in three days, and why.
8. At the end of three days, look at your results. Draw your plate as accurately as possible.
9. Measure any zones of inhibition around the spices and record the data. Share the data
with the entire class on the board.
10. Do the sizes of the zones vary from each other, or other groups?
11. Do your results match your hypothesis? Why or why not?
12. Prepare a one-minute report for the entire class. Include which spices you used, which
you think are the best and which you think are the worst at resisting this particular
bacteria.
2009 – 2010
28
How Can You Tell Evolution is Happening?
How Can You Tell Evolution is Happening?
Recognize that a change in gene frequency (the number of organisms that have a gene) in a
population over the course of years is an important aspect of biological evolution.
True or False?
1.
2.
3.
4.
A gene determines your physical traits. T / F
The reason that Africans have dark skin is because of the sun. T / F
Gene frequency is the number of populations that have a gene. T / F
Africans and Europeans are genetically very different. T / F
About Gene Frequency
A gene, or a characteristic that is part of your DNA, determines your traits. Genes have all
of the information that makes you who you are, including hair color, skin color, eye color, height,
and which hand you use to write. Since some characteristics are advantageous in certain
environments, what color and texture your hair is, the color of your skin and more all depend on
the environment where your ancestors were.
For example, people who come from southern
Africa typically have darker skin and darker hair than
Europeans or northern Africans. There is a good reason
for this. When sunlight hits human skin, our bodies use
that energy to make vitamin D. Vitamin D is necessary
for us to have strong muscles and fight disease, but we
can also get too much vitamin D. An excess of vitamin D
can cause your kidneys to fail and eventually result in
death! So, in areas where there is not a lot of sunlight, it
pays off to have light skin and absorb more sunlight and
therefore make more vitamin D. In areas with a lot of
sunlight, it pays off to have dark skin in order to not
absorb as much sunlight and avoid an excess of vitamin
D. Of course, there are many other reasons that we have
a certain skin tone. More importantly, our skin tone is not
just controlled by several different genes, it's also affected
by our environment!
Gene frequency refers to the amount of times in a
population that a certain gene happens. From our example above, we would expect that the genes
which cause a darker skin tone in humans have a higher frequency in Africa than in Europe. It is
much easier to talk about evolution when you can talk about the differences in gene frequencies
between different populations. When talking about human populations, the differences between an
African and a European are actually very small – even though they are very noticeable! If you
choose two random Americans that have similar skin color, facial features, height and weight they
will still have many genetic differences. In fact, they will have as many genetic differences as
between a light-skinned European and a dark-skinned African! As humans, we are all very complex
and have millions of small differences, some more noticeable than others.
True or False?
1. A gene determines your physical traits. T / F
2. The reason that Africans have dark skin is because of the sun. T / F
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Shaw High School
Evolution
3. Gene frequency is the number of populations that have a gene. T / F
4. Africans and Europeans are genetically very different. T / F
Questions
Do you remember?
1. What is a gene?
2. Define gene frequency.
3. List at least four genetic characteristics.
Think about it!
4. Explain why there is a difference in skin tone between Europeans and Africans.
5. Give an example of a gene that has different gene frequencies in different populations.
Do something!
6. If pollution continues on Earth, the ozone layer will let more and more sunlight in. Create a
timeline as to what will happen to the average skin tone of people in North America in 50
years. Then, write three sentences: what is your prediction, why you think that will happen
and a summary of your timeline.
Remember?
7. Describe the relationship between an independent and dependent variable.
8. What do animals breathe in? What do animals breathe out?
9. Which are the advantaged offspring in a population?
10. Did humans evolve from monkeys? Explain!
Sickle-Cell Anemia
Vocabulary
Hereditary
Prevalent
Immunity
Resistance
Spleen
Something that is given by parents to offspring
Common
Ability to completely fight off disease
Ability to fight off some amount of disease
An organ in the body that filters blood
From TeachersDomain.org
A gene known as HbS was the center
of a medical and evolutionary detective story
that began in the middle 1940s in Africa.
Doctors noticed that patients who had sickle
cell anemia, a serious hereditary blood
disease, were more likely to survive malaria, a
disease which kills some 1.2 million people
every year. What was puzzling was why sickle
cell anemia was so prevalent in some African
populations.
How could a "bad" gene -- the
mutation that causes the sometimes deadly
sickle cell disease -- also be helpful? On the
other hand, if it didn't provide some survival
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30
How Can You Tell Evolution is Happening?
advantage, why had the sickle gene stayed in the population at such a high frequency?
The sickle cell mutation is a like an error in the DNA code of the gene that tells the body
how to make a form of hemoglobin (Hb), the thing that carries oxygen in our blood. Every person
has two copies of the hemoglobin gene, one from their mother and one from their father. Usually,
both genes make a normal hemoglobin protein. When someone inherits two mutant copies of the
hemoglobin gene, the mutant form of the hemoglobin protein causes the red blood cells to lose
oxygen and warp into a sickle shape during periods of high activity, like running (see picture on the
left). These sickled cells become stuck in small veins and other blood vessels, causing a "crisis" of
pain, fever, swelling, and tissue damage that can lead to death. This is sickle cell anemia.
But it takes two copies of the mutant gene, one from each parent, to give someone the fullblown disease. Many people have just one copy, the other being normal. Those who carry the sickle
cell trait (have only one copy) do not suffer nearly as severely from the disease.
Researchers found that the sickle cell gene is especially prevalent in areas of Africa hard-hit
by malaria. In some regions, as much as 40 percent of the population carries at least one HbS
gene.
It turns out that, in these areas, HbS carriers have been naturally selected, because the trait
gives some resistance to malaria. Their red blood cells, containing some mutant hemoglobin, tend
to sickle when they are infected by malaria. Those infected cells flow through the spleen, which
removes them from the blood because of their sickle shape -- and malaria is eliminated along with
them.
Scientists believe the sickle cell gene appeared and disappeared in the population several
times, but became permanent after a particularly bad form of malaria jumped from animals to
humans in Asia, the Middle East, and Africa.
In areas where the sickle cell gene is common, the immunity that it gives has become a
selective advantage. Unfortunately, it is also a disadvantage because the chances of being born
with sickle cell anemia are relatively high.
For parents who each carry the sickle cell trait, the chance that their child will also have the
trait -- and be immune to malaria -- is 50 percent. There is a 25 percent chance that the child will
have neither sickle cell anemia nor the trait which gives immunity to malaria. Finally, the chances
that their child will have two copies of the gene, and therefore sickle cell anemia, is also 25
percent. This situation is an example of an evolutionary "trade-off."
Respond
1.
2.
3.
4.
5.
6.
In the photograph, what is pictured in the darker area?
What do sickle cells cause in the people who have them?
How do you get sickle cell anemia?
What effect does the sickle cell gene cause in people who only have one copy of the gene?
Why is the sickle cell gene still around if its effects can be so harmful?
What are the odds that the child of parents who each carry one normal gene and one sickle
cell mutation gene will have sickle cell anemia?
7. What are the odds that a child of two carrier parents will also be a carrier and, thus, be
protected from malaria?
Activities
S
Siicckkllee--C
Ceelll A
Anneem
miiaa
1. Choose a partner. In your pair, get two pennies.
2. One coin represents the genes of the mother and the other coin represents the genes of
the father. Each parent has one normal gene (H) and one mutated gene (h). If you flip
heads, then it is a normal gene (H), tails it is a mutated gene (h).
3. Study the genes and traits below:
Gene
Trait
Result
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Shaw High School
Evolution
S
Siicckkllee--C
Ceelll A
Anneem
miiaa
HH
Hh
No mutation
Normal
One normal gene, one mutated gene Protection from malaria
hh
Two mutated genes
Sickle cell anemia
4. Flip your coins 20 times and record your results below. After you have flipped, fill in the
traits that result. The first row is an example:
Gene from
Gene from
Gene for offspring
Trait
mother
father
(Coin from first
(Coin from second
person)
person)
H
h
Hh
Protection from malaria
5. Analyze your data by counting up the number of times (frequency) each trait occurs and
then total up the frequencies to get the percentage of the time that it shows up:
Trait
Frequency
Percentage
(Frequency / Total) x 100
Normal
Protection from malaria
2009 – 2010
32
How Can You Tell Evolution is Happening?
S
Siicckkllee--C
Ceelll A
Anneem
miiaa
Sickle cell anemia
Total
6. Get the entire class' data and fill in the following chart:
Trait
Frequency
Percentage
(Frequency / Total) x 100
Normal
Protection from malaria
Sickle cell anemia
Total
7. What advantage is there to having the mutated gene (h)? Hint: look at the individuals
who have only one mutated gene (h).
8. If having only one copy of the mutation did not provide protection from malaria, why
would the mutated gene (h) not last very long in the population?
9. If malaria was eliminated in Africa, predict what would happen to the presence of sickle
cell anemia. Is this considered evolution? Why or why not?
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Evolution
How Do We Name Organisms?
Biological classification represents how organisms are related with species being the most specific
part. Biologists arrange organisms into a hierarchy of groups and subgroups based on similarities
and differences which have to do with how closely related they are.
True or False?
1.
2.
3.
4.
5.
There are more than 10 million different species of living things. T / F
There are more species in each genus than in each kingdom. T / F
Dogs and humans are in the same family. T / F
Dogs and humans are in the same class. T / F
An amoeba is an example of an Animal. T / F
About Classification
Classification is a way of organizing anything into
categories so that we can figure out how those things are
similar to and different from each other. Any group of living
or non-living things can be classified. For example, we can
classify students according to many characteristics: your
grade level, credits earned, small school or age, among
other things.
There are between 10 and 100 million different
species of living things in the world. Scientists have only
named about 2 million of these species, and because they
keep finding new species all of the time, they estimate that
there must be many more species than already have been
found!
Because there are so many organisms in the world, it
is very important to be able to figure out how all of them
are related.
In order to do this, we use biological
classification.
The different levels of biological
classification are generally accepted to be, in order:

Kingdom

Phylum

Class

Order
An amoeba

Family

Genus

Species
According to many scientists, there are five major kingdoms: Animals, Plants, Fungi, Protists, and
Monera. This means that all organisms must fit into one of these kingdoms. For example, we are
in the Animal kingdom, trees and bushes are in the Plant kingdom, mushrooms and yeast are in
the Fungi kingdom, amoebas are in the Protist kingdom, and bacteria are in the Monera kingdom.
Within each kingdom, there are phyla (the plural of phylum). For example, the Animal kingdom
has over 9 major phyla, among them Chordata (like us), Insects, Arachnids (spiders) and
Arthropods (crabs). Then, there are several classes in the Chordata phylum, like Birds, Mammals,
Reptiles and Amphibians.
As you can see, every step you take on the classification list, the more specific it is. Once
you get down to the species level (like Homo sapiens), there is only one type of organism. This
organization of things is called a hierarchy because it lists the category that has the most things
2009 – 2010
34
How Do We Name Organisms?
first, and the category with the least things last.
Just as importantly, you can tell a lot about an organism based on where it's classified.
Because we and dogs are both in the same class (Mammals), that means that we are more closely
related to dogs than we are to spiders, as spiders are in a different phylum (Arachnids). If two
organisms are in the same genus, that means that they are very highly related. If they are only in
the same Kingdom, then that means that they are not very highly related at all.
Another view of classification, with the human classification on
the right
True or False?
1.
2.
3.
4.
5.
There are more than 10 million different species of living things. T / F
There are more species in each genus than in each kingdom. T / F
Dogs and humans are in the same family. T / F
Dogs and humans are in the same class. T / F
An amoeba is an example of an Animal. T / F
Questions
Do you remember?
1. List the order of biological classifications.
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Evolution
2. Which classification is the most general? The most specific?
3. What are the five kingdoms of living things?
Think about it!
4. A scientist hands you three insects, named Alpha, Beta and Charlie. She tells you that Alpha
and Beta are in the same family, while Alpha and Charlie are in the same order. Which
insects are most closely related?
5. Differentiate (tell the difference between) birds and reptiles in two ways.
Do something!
6. Create a new kingdom of living things that does not exist. Describe at least three
characteristics of your new kingdom, sketch one of the organisms, and name the kingdom
using the Latin and Greek roots.
Remember?
7. Describe homeostasis in your own words.
8. Why doesn't it matter what scientists think about natural selection?
9. Is there such a thing as scientific fact? Why or why not?
10. Define gene frequency.
Dichotomous Keys: Shapes
From MiddleSchoolScience.org
Dichotomous keys are a way to figure out the classification of a thing, living or non-living. You are asked a
series of questions, and by following the arrows or directions, you can then figure out what something is
called. These are often used in biology for scientists who are working out in the field. For example, a scientist
will see a tree and use a dichotomous key in order to figure out what kind of tree it is based on the type of
leaves, roots and trunk.
In the following example, you are going to be asked to classify the shapes according to their characteristics:
2009 – 2010
36
How Do We Name Organisms?
Activities
D
Diicchhoottoom
moouuss K
Keeyyss:: TTrreeeess
1. Collect leaf samples from five trees outside.
2. Come back inside and use http://www.oplin.org/tree/ to identify the five leaves. While
you are identify, make a note about each decision that you make.
3. From these five trees, write out your dichotomous key in the list format below.
4. Have one other group try your dichotomous key: what were their results?
Dichotomous Key for Furniture
1a. Has four legs
Go to 2
1b. Doesn’t have four legs
Go to 3
2a. You write on it
Desk
2b. Don’t write on it
Chair
3a. It rolls
Rolling chair
3b. Doesn’t roll
File cabinet
C
Cllaassssiiffiiccaattiioonn
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Evolution
[Note: You need an animal card to complete this assignment – and hand it back in when you’re
done!]
1. Put these classifications in the correct order: Order, Species, Kingdom, Class, Genus,
Phylum, Family
2. Come up with a way to remember the order of these classifications, for example: “King
Phillip Came Over For Great Sandwiches”. You can make a phrase like this, a drawing, or
any other way that includes every classification and helps you remember the
classifications. When you hand in the homework, you will be quizzed on the seven
classifications (it is worth 7 points of the grade), so don’t just copy off of someone else!
3. Using the animal card, identify all seven classifications for this animal (if the phylum is
missing, it’s “Vertebrates”) keeping in mind that the genus and species are directly below
the animal’s name on the back of the card.
4. Answer:
a) Which classification contains the most animals?
b) Which classification contains only one animal?
c) What is the relationship between the order of the classifications and the amount of
animals in each classification?
D
Diicchhoottoom
moouuss K
Keeyyss:: B
Beeaannss
1.
2.
3.
4.
Get a set of beans and a dichotomous key. For each bean:
Write down each decision that you make (e.g., “It is not round”, “It is all white”)
Write down the name of the bean
Identify which beans were not in your set, but were in the dichotomous key. What would
you expect each bean to look like, according to the information in the dichotomous key?
2009 – 2010
38
How Do We Know So Much About Life?
How Do We Know So Much About Life?
Geologic time can be estimated in many ways. For example, rock sequences, matching up fossils
and radiometric dating.
True or False?
1. Fossils tell us how old the Earth is. T / F
2. Scientists use rock sequences to figure out rock ages. T / F
3. Radiometric dating uses unstable chemicals like uranium to determine the age of
rock. T / F
About Geologic Time
The Earth is really old. Really, really, really old. We've already
seen that scientists estimate it's 4.5 billion years old. And we know that
this is quite a long time ago. But what's even more interesting is the fact
that it was so hot that there wasn't even any solid rock for about a billion
years. Then, once the outer layer of the Earth cooled down enough to be
solid (like the crust of a pizza), the inner part of the Earth was still hot
liquid magma. Of course, that magma wanted to come out by the action
of volcanoes, and so gases and water vapor ended up coming out of the
hot Earth and landing in the atmosphere. That water vapor cooled down
enough to become the ocean, which is where it's believed life began.
So there were these tiny, microscopic living things in the ocean.
Amazingly, some of them actually turned into fossils so that scientists
know that at least 3.5 billion years ago, these small organisms existed!
Furthermore,
scientists
find
these
organisms
inside
of
certain types of rocks that only
existed during a certain time period. By doing all sorts of
chemical testing, scientists can estimate how old a
particular type of rock is, and once they know that, they
know how old the fossils are inside of that rock. The
guides which help scientists all over the world figure out
how old rocks are is called a rock sequence.
One of the tests that scientists can do to figure out
the age of rock is called radiometric dating.
Radiometric dating uses processes that happen naturally
to be able to tell how old certain things are. For example,
you have a squirrel and an apple tree. Well, this squirrel
happens to like eating apples, but will only eat one per
day and leaves behind the core of the apple. One day,
A sample rock sequence
you happen to go past your apple tree and notice that
there are 90 apples and 10 apple cores. Assuming that nothing else happened with the apples or
the cores, you know that the squirrel has been eating apples for 10 days. If you went by the tree a
week later, you would expect to see 17 apple cores instead of 10.
Radiometric dating is very much like this. There are certain chemicals, like uranium, which
are radioactive and break down over time. They actually form other chemical elements, as
uranium will form lead, just like the squirrel in our example turned the apple into a core. Scientists
know how long it takes for uranium to break down into lead, so if they find some uranium and lead
together, they can figure out how long that uranium has been around, and therefore how old the
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Shaw High School
Evolution
rock is. For example, if 90% of the rock is uranium, then it's older than rock that's 95% uranium.
True or False?
1. Fossils tell us how old the Earth is. T / F
2. Scientists use rock sequences to figure out rock ages. T / F
3. Radiometric dating uses unstable chemicals like uranium to determine the age of
rock. T / F
Questions
Do you remember?
1. What is a fossil?
2. What can radiometric dating tell scientists?
3. Is there just one rock sequence? Why or why not?
Think about it!
4. If you compare the rock at the bottom of a rock sequence with the rock on top, what do you
know about how old the rock at the bottom is?
5. Carbon-14, which is an unstable chemical, breaks down to form carbon-12. If sample A has
a higher percentage of carbon-14 than sample B, then what do you know about the age of
sample A?
Do something!
6. Create a rock sequence (like the sample from the reading) from the following information:

Scientists found four layers of a rock sequence in Cairo, Egypt

A fish fossil, Aleph, was found in a layer of conglomerate

The layer of granite was the oldest rock found in Cairo

A dinosaur fossil, Beth, was found in a layer of limestone

A layer of shale was found in between the conglomerate and limestone

Beth was found to have a lower percentage of carbon-14 than Aleph
Remember?
7. Explain why science doesn't have firm answers to questions.
8. Is evolution happening right now?
9. List at least four genetic characteristics.
10. List the order of biological classifications.
Rocks Tell Tale of Warm Early Atmosphere
Vocabulary
Abundance A great deal of
Greenhouse Gas Any gas that causes heat to stay inside the atmosphere
Methane A gas that is often burned and is one of the greenhouse gases
Geologic Footprint The record of what has happened on Earth that is buried in rocks
Field Geologist Someone who studies the Earth outside of a laboratory and actually out at
sites like mountains, rivers and forests
Analysis Using the results of an experiment to come to some conclusions about the
2009 – 2010
40
How Do We Know So Much About Life?
experiment
Sediment Tiny rocks that fall out of water and gather on the floor or a river, lake or
ocean
Regeneration The process that creates something over again
By Dawn Levy, Stanford News Service
If a time machine could take us back 4.6 billion years to the Earth's birth, we'd see our sun shining
20 to 25 percent less brightly than today. Without an earthly greenhouse to trap the sun's energy
and warm the atmosphere, our world would be a spinning ball of ice. Life may never have evolved.
But life did evolve, so greenhouse gases must have been around to warm the Earth. Evidence from
the geologic record indicates an abundance of the greenhouse gas carbon dioxide. Methane
probably was present as well, but that greenhouse gas doesn't leave enough of a geologic footprint
to detect with certainty. Oxygen wasn't around, indicate rocks from the era, which contain iron and
carbon instead of iron and oxygen. Stone fingerprints of flowing streams, liquid oceans and
minerals formed from evaporation confirm that 3 billion years ago, Earth was warm enough for
liquid water.
Now, the geologic record revealed in some of Earth's oldest rocks is telling a surprising tale of
collapse of that greenhouse -- and its subsequent regeneration. But even more surprising is the
critical role that rocks played in the evolution of the early atmosphere.
"This is really the first time we've tried to put together a picture of
how the early atmosphere, early climate and early continental
evolution went hand in hand," said Donald R. Lowe, a professor of
geological and environmental science who wrote the paper with
Michael M. Tice, a graduate student investigating early life. "In the
geologic past, climate and atmosphere were really [heavily] influenced
by development of continents."
The record in the rocks
To piece together geologic clues about what the early atmosphere was
like and how it evolved, Lowe, a field geologist, has spent virtually
every summer since 1977 in South Africa or Western Australia
collecting rocks that are, literally, older than the hills. Some of the
Earth's oldest rocks, they are about 3.2 to 3.5 billion years old.
Geologists Mike Tice, left,
and Don Lowe display
rocks that point to a warm
ancient Earth with more
carbon dioxide in its
atmosphere than today,
which likely supported a
surface temperature of 70
degrees Celsius (158 F).
"The further back you go, generally, the harder it is to find an
[unchanged] record, rocks that haven't been twisted and squeezed ...
and otherwise altered," Lowe says. "We're looking back just about as
far as the sedimentary record goes."
After measuring and mapping rocks, Lowe brings samples back to
Stanford to cut into sections so thin that their features can be revealed
under a microscope. Scientists participate in analyses that further
reveal the rocks' histories.
The geologic record tells a story in which continents removed the
greenhouse gas carbon dioxide from an early atmosphere that may
have been as hot as 70 degrees Celsius (158 F). At this time the Earth was mostly ocean. It was
too hot to have any ice caps. Lowe hypothesizes that rain combined with carbon dioxide to make
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Evolution
carbonic acid, which caused the erosion of mountains of newly formed continental crust. Carbonic
acid formed bicarbonate, which was carried down rivers and streams to be left behind as limestone
and other minerals in ocean sediments.
Over time, great slabs of oceanic crust were pulled down, or subducted, into the Earth's mantle.
The carbon that was locked into this crust was essentially lost, tied up for the 60 million years or so
that it took the minerals to get recycled back to the surface or passed through volcanoes.
The hot early atmosphere probably contained methane too, Lowe says. As carbon dioxide levels
fell, the amount of carbon dioxide and methane became about equal. This blocked out light and
caused further cooling, perhaps a temperature drop of 40 to 50 degrees Celsius (100 F).
Eventually, about 3 billion years ago, the greenhouse just collapsed, Lowe and Tice theorize, and
the Earth came into its first ice age 2.9 billion years ago.
The rise after the fall
Here the rocks reveal an odd twist in the story -- regeneration of the greenhouse. Recall that 3
billion years ago, Earth was essentially Waterworld. There weren't any plants or animals to affect
the atmosphere. Even algae hadn't evolved yet, only small unicellular organisms that produced
some methane. Carbon continued to be subducted into what Lowe calls "a big storage facility ...
that kept most of the carbon dioxide out of the atmosphere."
But as carbon dioxide was removed from the atmosphere and put into rock, there was less carbonic
acid to erode mountains and the mountains were becoming lower. But volcanoes were still spewing
into the atmosphere large amounts of carbon from deep within the ocean.
"So eventually the carbon dioxide level climbs again," Lowe says. "It may never return to its full
glorious 70 degrees Centigrade level, but it probably climbed to make the Earth warm again."
Over the past few million years we have been going back and forth between ice and non-ice ages,
Lowe says. We are in a non-ice age right now. It's a transition -- and scientists are still trying to
understand how big global climate change caused by humans in recent history is compared to that
caused by nature over the ages.
"If we can analyze ancient climates, atmospheres, and life, we can take some first steps at
understanding what is happening today and likely to happen tomorrow."
Respond
1.
2.
3.
4.
5.
6.
7.
What could have caused life to never have evolved?
When did Lowe and Tice think that the Earth was warm enough for liquid water?
How old are the oldest rocks found on Earth?
What chemical caused the mountains to erode on early Earth?
What caused the greenhouse collapse that led to Earth's first ice age 2.9 billion years ago?
What made the levels of carbon dioxide go up again after the first ice age?
Make a diagram showing the inside and outside of the Earth, along with a mountain, volcano
and clouds. Use arrows and labels to demonstrate where carbon came from and went to
inside and outside the Earth in this article.
2009 – 2010
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How Do We Know So Much About Life?
Geologic Time Scale
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Evolution
Activities
2009 – 2010
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How Do We Know So Much About Life?
FFoossssiillss
All living things are made up of a few main chemical elements, like carbon. When living things
die, many different things can happen to them. For instance, they can be broken down by
decomposers, eroded by water or wind, or even crushed by other animals. Very rarely,
something happens called fossilization, when the carbon inside the now dead organism hardens
into what we call a fossil.
For each of the six boxes, do the following (refer to the time scale):
1. What era and period do these fossils come from?
2. What age range are these fossils?
3. Pick three of the fossils, sketch them and write down the scientific name. For each fossil,
find a common name by looking on the internet, looking through the biology book, or
asking someone who has already investigated this fossil.
FFoossssiillss O
Ovveerr TTiim
mee
Using
1.
2.
3.
your fossil work, in groups of three, do the following:
What is the name of the phylum (and common name) of the oldest fossil that you drew?
What is the name of the phylum (and common name) of the newest fossil that you drew?
For each box, in order from oldest to most recent:
a) Give two characteristics that the previous organisms did not have
b) What environments were these organisms well-suited for?
4. Create a sign for the room’s timeline using the cardstock up front. Write the name of the
phylum big and clear! Include a sketch, drawing, or picture on at least one side of the
sign and tell me where on the timeline it should go.
OGT Review
1. A student is studying several species that belong to the plant kingdom. Which two are most
closely related?
a) Ficus benjamina and Ficus lyrata
b) Castilla elastica and Ficus elastica
c) Bromus japonicus and Ipomoea violacea
d) Fermaldia pandurata and Ficus pandurata
2. The following diagram is found in an evolutionary biology textbook.
This branching tree diagram is most likely used to represent the theory that suggests
a) new species arise throughout time following rounds of mass extinction.
b) all species share a common ancestor and that change occurs through time.
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Shaw High School
Evolution
c) speciation occurs very quickly with long periods of no change in between.
d) all species originated during the same period and some have subsequently gone extinct.
Use the following to respond to questions #3 - 5:
The monarch is a bright orange butterfly with black stripes. It acquires toxins from the
milkweed plants it eats as a caterpillar. Adult monarchs retain these chemicals. Experiments
have shown that blue jays that eat poisonous monarchs become sick within 15 to 30
minutes. The viceroy is also an orange, black-striped butterfly, which is difficult to distinguish
from a monarch. Viceroy larvae consume primarily non-toxic poplar or willow tree leaves.
Scientists have long suggested that viceroys have avoided predation by mimicking the
monarch’s coloration pattern. New evidence indicates that this may not be the case.
Descriptions of two sets of experiments with monarchs and viceroys are given below.
Experiment 1 (1958): Blue jays that were raised in captivity were offered viceroys. The
hungry jays devoured the viceroys. The same jays were offered monarchs. After eating one
or two monarchs, the blue jays refused to eat monarchs or viceroys. All butterflies’ wings
were intact when given to the birds.
Experiment 2 (1991): Researchers fed the wingless abdomens of monarch, viceroy, queen,
and non-toxic control butterflies to red-winged blackbirds and monitored the percentage of
each type eaten. While 98% of control butterflies and 70% of queen butterflies were eaten,
only 40% of viceroys and 40% of monarchs were eaten.
3. What statement regarding the similarities between monarchs and viceroys best agrees with
Charles Darwin’s theory of natural selection at the time of its publication in 1859?
a)
b)
c)
d)
Monarch butterflies are an older species than viceroy butterflies.
Similarities between monarch and viceroy butterflies result from their diets.
Viceroy butterflies avoid predation due to their resemblance to monarch butterflies.
Variations in DNA sequences are responsible for the similarity between monarch and
viceroy butterflies.
4. The diagram below shows a partial classification scheme for monarch and viceroy butterflies.
2009 – 2010
46
How Do We Know So Much About Life?
Based on this diagram, monarchs and viceroys belong to the same
a)
b)
c)
d)
Genus
Family
Species
Subfamilies
5. A scientist studying a large population of a particular species of bird concludes that monarch
butterflies are toxic to that bird species. However, upon studying a second, smaller
population of the same bird species, he discovers that the second population is able to eat
monarchs without becoming sick.
How could the scientist best explain his findings?
a)
b)
c)
d)
The larger bird population has a small gene pool.
Monarchs are only toxic if eaten in large quantities.
Genetic drift has occurred in the smaller population.
Natural selection has increased populations of non-toxic butterflies.
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Shaw High School