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Lesson 22: The Theory of Evolution (3.4.1)
DEVELOPMENT OF EVOLUTIONARY THOUGHT
Scientists observe the natural world and come up with questions.
How can a rhea in South America, an ostrich in Africa and an emu
in Australia look so much alike but be different birds? How can the
finches on Galapagos Islands all have different beaks? How can
sharks and dolphins have similar-looking structures when one is a
fish and one is a mammal? The theory of evolution attempts to
answer such questions and more. The theory of evolution states that organisms go
through a process of change over time and develop new species from preexisting ones.
Phylogeny is the evolutionary history of organisms or a group of related organisms.
In 1809, the year Charles Darwin was born Jean Baptise Lamarck
published a book on his theory of evolution based on comparison of
species at the Paris museum where he worked. Lamarck’s two popular
ideas were: use and disuse, the idea that body parts were used most
often became stronger and those used less often got smaller and became
nonfunctional. His second idea was acquired characteristics. Lamarck
reasoned that the long neck of a giraffe was a result of the organism
gradually acquiring these characteristics by stretching its neck to reach food. An
organism could acquire a characteristic through its actions to survive.
DARWIN
Charles Darwin developed a passion for studying biology and geology while studying
for the ministry after leaving medical school at Cambridge in England.
Through the efforts of his professors, he was able to get aboard a British
science ship, the Beagle, bound on a five-year trip with a mission to chart
poorly know stretches of the South American coastline. During the trip,
Darwin observed many adaptations of plants and animals that inhabit a
variety of environments. He observed that the finches on the Galapagos
Islands looked similar to one type of finch on the South American
continent, but none of the Galapagos Island types of finches were found
on the South American mainland.
Darwin began to ask many questions; one of which began to
plague him above all others: “How did one species change into
a different species? It is important to note that scientists in the
19th century did not know how a trait passes from one animal to
its offspring; they did not know of the existence of DNA.
After a trip on the Beagle, Darwin studied his collection of organisms as well as many
different books and readings. He also talked with several domestic animal breeders and
read principles of geology. Observations that Darwin made helped him conclude that
environmental pressures change how organisms interact with their environment.
Darwin observed the entire diet of the Galapagos finches change in response to their
isolated environment. The pressure for modification of behavior (eating habits) caused
the finches that were more able to adapt to survive and some migrated to other islands.
After twenty years of study, Darwin published his book, The Origin of Species in 1859.
Two concepts that are widely studied from Darwin’s research are common ancestry and
natural selection.
To be clear: the individual physical traits of a finch are not modified by the finch (his
beak does not grow and change o suit his changing needs). Rather, the animals who
already possess a trait that is favored by the current environmental pressures survive and
pass that trait on to their offspring. This insures that, over time, the expression of the
favored trait becomes more pronounced, and other traits disappear. This is why Darwin’s
theory of natural selection is also called the survival of the fittest
MODERN IDEAS
Darwin’s ideas, along with Mendel’s work and the work of others, have lead to modern
ideas about evolution. These ideas include:
1. There are several mechanisms responsible for evolution of organisms. One of the most
important is genetic drift (random change in genes), which occurs through natural
selection. The change in gene frequency is results of genetic drift.
2. Characteristics that are inherited are carried by genes, and natural variation within a
population is the result of several alleles working together.
3. Speciation (formation of new species) can occur due to isolation of a single species,
nonrandom mating, and sexual selection and disease agents resulting in variations
in genes that accumulate.
In the 17th century, two scientists did experiments which
disproved abiogenesis. Abiogenesis is the idea that living
organisms can come from non-living things. For example,
scientists believed frogs came from mud or mice came from
wheat grain wrapped in dirty, sweaty rags. Louis Pasteur’s
experiment, see Figure 22.5, used a Swan-necked flask with
a S-shaped top that did not allow microorganisms into the
flask. Pasteur boiled the broth in the flask to kill any
bacteria and microorganisms and then let it sit. There was
no growth in the flask. Pasteur then broke off the top and
allowed the flask to sit, exposed to the air around it. Within
just a few days, it was cloudy with growth from microorganisms. It was not until the
broth in the flask was exposed to the air, and the microorganisms in the air, that there was
growth! Francesco Redi in 1668, see Figure 22.6, set up a different experiment to test
the same idea. Redi used jars with rotten meat in them. He covered half the jars with
cheese cloth, which did not allow any flies or other insects into the jar. The other halves
of the jars were left open, allowing flies and insects
to go in and out. Only the un-covered jars had
maggots appear on the rotten meat. The flies laid
eggs, which developed into maggots. The covered
jars did not have maggots appear, because no flies
were able to enter the jars and lay eggs. Redi’s
experiment confirmed that life can only come from
living organisms. Recall that a characteristic of
living organisms is all living organisms reproduce.
This idea is known as biogenesis: life comes from
life.
THE EARLY EARTH
The Earth’s early atmosphere was far different
from what we see today. Using advanced
technology to date fossils, scientists agree that
Earth is around 4.55 billion years old. The
oldest rocks found on Earth are 3.8 billion
years old. During much of that time, only
bacteria (prokaryotic cells) inhabited the
Earth. Eukaryotic cells have only developed
in the past 1.8 billion years.
Scientists speculate that there was no free
oxygen in the Earth’s early atmosphere.
Therefore, the first living organisms were
probably anaerobic organisms, meaning they
did not need oxygen. The atmosphere was
believed to consist of gases that were released
from volcanic activity occurring underneath the surface of the Earth. As photosynthetic
life developed, the process of photosynthesis resulted in the creation of atmospheric
oxygen. Most of the oxygen build-up in the atmosphere was a result of photo-autotrophs
such as cyanobacteria (bacteria with bluish-green pigments). These organisms captured
the energy of the sun to make food and released oxygen as a waste product. Little by
little they turned the atmosphere into breathable air, opening the way to the diversity of
life that followed.
PROKARYOTIC AND EUKARYOTIC EVOLUTION
It is believed that the first life forms were prokaryotic, heterotrophic (meaning they get
their energy by consuming organic matter), and anaerobic. These prokaryotic organisms
most likely consumed the same organic matter that they formed from. Over time, the
organic matter in the ocean decreased and evolution of autotrophic organisms that make
their own food, were favored. Autotrophic organisms released oxygen into the
atmosphere, and eventually there was enough oxygen in the atmosphere that evolution
favored aerobic organisms, require oxygen for cellular respiration.
Recall eukaryotic organisms did not appear on Earth until close to 2 billion years after
prokaryotic cells. Eukaryotic cells are larger and more complex than prokaryotic cells.
The endosymbiotic theory helps explain how eukaryotic organisms may have evolved.
It is believed that prokaryotic organisms provided an environment for eukaryotic
organisms to evolve due to a mutual symbiotic (living together) relationship. This
beneficial relationship eventually leads to the formation of independent eukaryotic cells
which have organelles that are more specialized than prokaryotic cells.
Today’s atmosphere mostly contains nitrogen, oxygen carbon dioxide and water vapor.
The idea that the atmosphere evolved today’s different gases is supported by rock
samples drilled from different layers of Earth’s crust. These rocks were deposited during
ancient volcanic eruptions.
In the 1920’s, A. I. Oparin proposed that the Earth’s early atmospheric gases were
water vapor, hydrogen gas, methane, and ammonia. Miller and Urey set up an apparatus
similar to Figure 22.7 to test Oparin’s proposed early atmospheric gases to determine if
these gases provided elements to form the first molecules necessary for life. Miller and
Urey combined the proposed gases in early Earth’s atmosphere, and simulated lightning
(energy) by touching two electrodes to create an electric spark. They then allowed the
water vapor to cool, to simulate rain. When they analyzed this rain water, they found
diverse organic compounds and some amino acids. Recall amino acids are the monomers
of proteins, and essential for life because proteins regulate cells and help keep them in
homeostasis.
Activity 1
1. According to I.A. Oparin, the early atmospheric gases of the earth were believed to be:
A. water vapor (H2O), hydrogen gas (H2), methane (CH4), and ammonia (NH3)
B. carbon (C), hydrogen gas (H2), methane (CH4), and ammonia (NH3)
C. helium (He), Carbon (C), hydrogen gas (H2), and methane (CH4)
D. ammonia (NH3), Carbon (C), hydrogen gas (H2), and methane (CH4)
Use the diagram below to help you answer Question 2.
2. Explain how Miller and Urey’s apparatus contributes to our understanding of the
origin of organic compounds. Recall amino acids are the monomers of proteins,
and essential for life because proteins regulate cells and help keep them in
homeostasis.
THE FOSSIL RECORD AND EVIDENCES OF EVOLUTION
According to the theory of evolution, a change in a population of species occurs over a
period of time. Why is it important to know that organisms change over time? The
answer is that if there is change, then there must be a cause of the change. Discovering
both the cause of and the mechanism through which the change occurs is central to the
survival of organism and ecosystems they populate. Scientists believe evidences of these
changes exist in the fossil record, biochemical properties and anatomical structures.
Other evidences come from various disease agents such as bacteria, viruses and
chemicals because these are thought to influence changes in organisms that could serve
as sources for natural selection. Evidence supports that new species that evolve from
preexisting species over long periods show great biodiversity.
THE FOSSIL RECORD
Fossils provide evidence for the change in organisms over time. A fossil is the remains
of an organism that lived in the past. Most fossils are found in sedimentary rocks. These
remains can be in the form of casts, and imprints, or calcified bones. The study of fossils
gives us a fascinating historical perspective – snapshots from an Earth of long ago taken
together, these snapshots are referred to as the fossil record. The existence of animal life
on land is relatively recent. Fossils indicate that insects first came onto land around 440
million years ago (mya), and vertebrate animals moved onto land about 417 mya.
Scientists use the body of evidence accumulated from the fossil record to make
hypotheses about organisms of the past and how they are related to the diverse organisms
that exists today.
RELATIVE AND ABSOLUTE DATING
Fossils have another use: they allow scientists to date rock formations. This process is
called relative dating, and it depends on the identification of an index fossil. An index
fossil is the remains of animal that existed during a very defined period in history.
Trilobites are fossilized arthropods that existed over 300 mya in ancient seas during the
Cambrian period and became extinct by the end of the Devonian period. Trilobites have
been used extensively to predict the age of fossils found in the same rock stratum as
trilobites. Relative dating is a powerful tool; however, not all fossils are index fossils so
there must be another way to date these fossils.
Radioactive dating is a type of absolute dating, which uses radioactive elements to
determine the age of rocks and fossils. These radioactive elements break apart in a
process known as radioactive decay. The decay happens at a measurable rate with a
half-life that is characteristic of the radioactive element. Half-life is the time required for
one-half of the radioactive isotope to decay. Carbon -14 has a half-life of 5,730 years.
Using the known half-life of carbon-14, scientists can determine the age of the fossil. For
example, let’s imagine that upon an animal’s death, it contains 15 grams of radioactive
carbon-14 and 60 grams of nonradioactive carbon -12. Complete the information in the
chart to determine the age of the organism. If an organism is older than 50,000 years,
then another radioactive isotope such as uranium-238 or potassium 40 may be used to
determine the age of the organism.
Activity 2
Use the table below and the information provided to answer each of the questions below.
Nonradioactive carbon-12
Radioactive Carbon-14
Measurable rate of decay
Carbon-12 = 60 grams
Carbon-14 = 60__ grams Original amount of C12/C-14
Carbon-12 = 60 grams
Carbon -14 = _____grams After first half-life
( 5, 730 years)
Carbon- 12 = 60 grams
Carbon-14 = _15__ grams After second half-life
(5,730 years)
Age of fossil based on total years for measurable rate of
______ years
decay
1. An arthropod fossil is discovered that contains 60 grams of carbon-14 and 60 grams of
carbon-12. How many grams of carbon-14 remain after the first half-life?
2. How old is the arthropod fossil?
GAPS IN THE FOSSIL RECORD
The fossil record is an important tool scientists use when attempting to better understand
the history of the Earth; however, it is important to note the record itself is not complete.
All scientists agree that there are gaps in the fossil record. There
are periods of time that organisms seem to either disappear
because fossils are not found or organisms seem to rapidly evolve
without apparent explanation. Estimates indicate that the fossil
record only represents 0.1% of the organisms that have lived on
the planet. Most organisms are either eaten or decomposed; it is
very rare that an organism will actually become fossilized. This
is one possible explanation for these gaps.
BIOCHEMICAL SIMILARITIES
Biochemical similarities demonstrate relationships among various organisms. DNA
sequences are studied and compared. The closer the sequences, the more closely related
the organisms.
Humans and chimpanzees show a great deal of overlap in their
DNA sequences. Humans and reptiles show some similarities, but
there is less overlap between these two sequences than between the
human and chimpanzee sequences. When the DNA from humans
and yeast are compared, there is very little overlap. This suggests
that humans and chimpanzees are much more closely related than
humans and yeast. Examine Figure 9.12 to see how one
chromosome can vary between different organisms. Another
example is the horseshoe crab. The horseshoe crab was once
grouped with crabs, but is now grouped with the spiders based on
genetic data.
ANATOMICAL EVIDENCE
Ancient organisms are thought to come from a common
ancestor based on similar bone
structures and similar embryos.
Appendages such as the arms of
man and the forelimbs of cats,
whales and bats have similar bone
structure, but very different
functions. Bone structures in the
wings of birds and the forelimbs of
man and whale also show great similarity. Characteristics such as these that are possibly
the result of a common ancestry is referred to as homology. The homologous structures
from a variety of mammals are evidence of the evolutionary history of organisms or
phylogeny. Some structures called vestigial organs are simple in design such as the
appendix of man and it has little function if any to the organism. Vestigal organs are
thought to be traces of organs that had important functions in their ancestors.
Homologous embryos are similar in appearance and show similar distinct developmental
structures during the early stages. Vertebrates have grooves beneath the head and gill
pouches during the early developmental stages. These anatomical similarities are said to
be evidence for common ancestry.
Lesson 22 Review: The Fossil Record and Evidences of
Evolution
A. Define the following terms.
Theory of evolution
phylogeny
Acquired characteristics
Darwin
fittest
Abiogenesis
biogenesis
organisms
Endosymbiotic theory
Oparian
Early atmospheric gases
index fossil
dating
Absolute dating
half-life
biochemical similarities
homologous structure
Lamark
speciation
use and disuse
survival of the
aerobic organisms
anaerobic
Miller and Urey
relative dating
fossil
radioactive
common ancestor
vestigial organ
homologous embryo
B. Choose the best answer.
1. A fossil recognized as unique to certain time period is known as what?
A. an index fossil
C. a marker fossil
B. a distinct fossil
D. a time marker fossil
2. Why is it difficult to find fossils of cells?
A. because none exist
B. because humans cannot dig deep enough into the Earth
C. because no catastrophic events occurred in the ecosystems of the early Earth
D. because cells have no hard parts with large amounts of minerals that will fossilize
3. Wisdom teeth are the common name for the third molar in humans. They generally
appear
much later than all other adult teeth, and usually not until the age of 18. The teeth
have no
noticeable purpose to the modern human and are often pulled to make room for the
other teeth
in the mouth. The continued presence of wisdom teeth is a good example of
A. Homologous structures in humans
C. genetic diversity in humans
B. Vestigial structures in humans
D. adaptation to better dental
4. Evidences of evolution such as homologous structures, homologous embryos, DNA
sequence,
and chemical evidence support
A. abiogenesis
C. common ancestry
B. phylogeny
D. biogenesis
5. Ideas about evolution
A. were established in the 1900s
B. are perfect and need no refinement
C. may change based on new data
D. only involve animal species
6. The theory of evolution states that organisms go through a process of change over time
and
develop new species from preexisting ones. What term describes this evolutionary
history?
A. change
C. genetic drift
B. biogenesis
D. abiogenesis
7. What two main ideas did Darwin proclaim in his theory of evolution?
A. survival of the fittest and phylogeny C. natural selection and common ancestry
B. Speciation and common ancestor
D. phylogeny and speciation
8. Scientists observed flies on rotten meat and discovered flies came from eggs that were
laid on the meat. Discovering the stages of a fly shifted scientist belief from:
A. abiogenesis to biogenesis
C. use and disuse to acquired
characteristics
B. evolution to use and disuse
D. phylogeny to survival of the
fittest
9. When is it hypothesized that the first living organisms appeared on earth
A. 3.8 billion years ago
C. 440 million years ago
B. 1.8 billion years ago
D. 3.8 million years ago
10. What lead to the production of oxygen in the Earth’s atmosphere?
A. a change in the gases emitted from volcanoes
B. the weathering of ancient rock formations
C. the development of oxygen-producing life forms
D. the gases released from the decay of fossils
11. Which theory explains how eukaryotes evolved as separate organisms from
prokaryotes?
A. evolution
C. phylogeny
B. endosymbiosis
D. common ancestry
C. Complete the following exercises
1. Explain the difference between relative dating and absolute dating
2. Some scientists think biochemical evidence in DNA is more conclusive evidence for
evolution as compared to fossil record. Find information on the Internet to support
this claim
and give a one paragraph summary.
3. Look at the illustration of sedimentary rock with fossils embedded. Identify the two
oldest
and youngest fossils. Explain your reasoning.
4. Compare the two main ideas of both Darwin and Lamarck.
5. Explain how Mendel’s principles and other scientists work were used to modernize
Darwin’s theory.
6. Distinguish between an anaerobic organism and an aerobic organism. Use other
sources to give examples of each.
7. The basic structure of amino acids consists of the elements carbon, hydrogen, nitrogen
and oxygen. Explain how organic compounds from Miller and Urey’s experiment relate
to the early atmospheric gases.