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Transcript
Name__________________________________________________Date____________________Pd__________
Early Ideas about Evolution
Evolution is the process of biological change by which descendants come to differ from their ancestors.
Much of today’s understanding of evolution is based on Charles Darwin’s work in the late 1800s.
Carolus Linnaeus came up with a system to organize and name all of the different types of organisms or
species. A species is a group of organisms that can reproduce and have fertile offspring.
Lamarck was struck by the similarities of many of the animals he studied. It led him to argue that life was not
fixed. When environments changed, organisms had to change their behavior to survive. If they began to use
an organ more than they had in the past, it would increase in its lifetime. If a giraffe stretched its neck for
leaves, for example, a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit
the longer neck, and continued stretching would make it longer still over several generations. Meanwhile
organs that organisms stopped using would shrink. This theory was later found to no be true.
Theories of geologic change set the stage for Darwin’s theory
Fossils are traces of organisms that existed in the past. The locations of fossils in different rock layers
provide clues about Earth’s past. Ideas about how rock layers formed and changed:
Catastrophism – the ideas that past natural disasters like floods and volcanic eruptions shaped landforms,
causing species to become extinct in the process.
Gradualism – the idea the landforms were shaped by very slow changes over a long period of time
Uniformitarianism – the same processes that shaped landforms in the past also shape landforms today, so
they are the same (or uniform) through time
Darwin observed differences among island species
Darwin noticed that there was variation (differences in physical traits) between species on different islands.
He found finches with thick beaks in areas with large hard-shelled nuts, and finches with smaller beaks in
areas where fruits were available. Darwin realized that species are able to adapt to their surroundings. An
adaptation is a feature that allows an organism to better survive in its environment.
Darwin observed fossil and geologic evidence supporting an ancient earth
Darwin found that some fossils, like the giant armadillo (Glyptodon) looked similar to living species. This
suggested that the living species might have some relationship to the fossil forms. In order for such changes
to occur, Darwin figured that Earth must be much older than 6000 years.
Darwin found a lot of evidence supporting the ideas of uniformitarianism. For example, he found fossil
shells of marine organisms high up in the Andes Mountains. Later he experienced an earthquake and saw land
that had been underwater get shifted up above sea level. Observations like these led him to conclude that
daily geologic processes can add up to much bigger changes over a long period of time.
Several key insights led to Darwin’s idea of natural selection
Variation of similar species among islands, fossil evidence, and geologic events convinced Darwin that
evolution occurs.
Here are some of Darwin’s reasonings as to how it occurs that led him to his idea for natural selection:
Artificial Selection –Darwin noticed that plants and animals that are raised by humans had variations not seen
in their wild relatives. In artificial selection, humans select individuals with traits they desire and breed them
to produce more individuals with those traits. Ex. Scientists develop a new color in roses.
Heritability – In order for traits to be selected they must be heritable. Heritability is the ability of a trait to be
passed down from one generation to the next. Things that are acquired, like a broken bone, are not heritable.
Natural Selection – Darwin reasoned that a process similar to artificial selection could happen in nature. In
artificial selection, humans are the selective agent. In natural selection, the environment is the selective
agent. Natural selection is a process in which individuals that have inherited beneficial adaptations produce
more offspring than do other individuals.
Struggle for Survival – Resources like food, water, and shelter were limits to population growth. Darwin
reasoned that a similar struggle happens in nature.
Natural selection explains how evolution can occur
There are four main principles to the theory of natural selection:
Variation. Individuals of a species differ due to genetic variation. Heritable differences are the basis for
natural selection.
Overproduction. Organisms have more offspring than can survive. This results in competition among
offspring for resources.
Adaptation. Some individuals have certain variations that allow them to survive better than other individuals
in their environment. These individuals are “naturally selected” to live longer and produce more offspring that
also have those adaptations.
Descent with modification. Over time, natural selection will result in species with adaptations that are
beneficial for survival and reproduction in a particular environment. More individuals will have the trait in
every following generation, as long as the environmental conditions stay the same.
Fitness is a measure of the ability to survive and reproduce. Individuals are “fit” if the possess a trait that
allows them to survive and reproduce successfully in the environment.
Natural selection cannot make new alleles – it does not change genetic material directly. Natural selection
acts on existing physical traits.
Peppered Moth
An example of evolution resulting from natural selection was discovered among "peppered" moths living near
English industrial cities. These insects have varieties that vary in wing and body coloration from light to
dark. During the 19th century, sooty smoke from coal burning furnaces killed the lichen on trees and darkened
the bark. When moths landed on these trees and other blackened surfaces, the dark colored ones were
harder to spot by birds who ate them and, subsequently, they more often lived long enough to
reproduce. Over generations, the environment continued to favor darker moths. As a result, they
progressively became more common. By 1895, 98% of the moths in the vicinity of English cities like
Manchester were mostly black. Since the 1950's, air pollution controls have significantly reduced the amount
of heavy particulate air pollutants reaching the trees, buildings, and other objects in the environment. As a
result, lichen has grown back, making trees lighter in color. In addition, once blackened buildings were
cleaned making them lighter in color. Now, natural selection favors lighter moth varieties so they have become
the most common. This trend has been well documented by field studies undertaken between 1959 and 1995
by Sir Cyril Clarke from the University of Liverpool. The same pattern of moth wing color evolutionary change
in response to increased and later decreased air pollution has been carefully documented by other researchers
for the countryside around Detroit, Michigan. While it is abundantly clear that there has been an evolution in
peppered moth coloration due to the advantage of camouflage over the last two centuries, it is important to
keep in mind that this story of natural selection in action is incomplete. There may have been additional
natural selection factors involved.
Evidence for Evolution
Genetic inheritance was not known in Darwin’s time, but Darwin supported his ideas with evidence from many
other sources – fossils, geography, embryology, and anatomy.
Fossils. Fossilized organisms are different in different rock layers. More ancient organisms are on the bottom
and more recent organisms are on top.
Biogeography. Different variation of species were found on different islands with different food sources,
climates and predators. Biogeography is the study of the distribution of organisms around the world.
Embryology. Embryos of different species may look similar. This suggests evolution from a distant common
ancestor.
Anatomy
Homologous structures - features that are similar in structure, but have different functions
Vestigial structures – small leftover organs or structures that had a function in an early ancestor. Ex.
Snakes and whales have small pelvic bones, suggesting that their ancestors were four-legged animals.
1. Draw a box around the name of the scientist that thought that if a organism used a structure too much it
would grow and be passed down to their offspring.
2. Underline twice the word that describes how landforms are created by spectacular events such as
volcanoes and earthquakes.
3. What is variation? _____________________________________________________________________
4. Highlight what Darwin discovered about finches on different islands.
5. Circle the definition of natural selection.
6. Draw a box around the statement that shows what Darwin learned from examining the Glyptodon fossil.
7. Underline twice the statement that explains what Darwin concluded after observing marine organisms in
the Andes Mountains.
8. Draw an X through the term that is represented by humans breeding plants and animals for favorable traits.
9. Circle twice the selective agent for natural selection.
10. What is fitness? _____________________________________________________________________
11. Does natural selection act on, or form new genetic material? ____________ Draw a line (lightly and with
pencil) through the statement that supports your answer.
12. Give an example of a vestigial structure. __________________________________________________
13. Circle the definition for Biogeography.
14. What is suggested by the similarity of early embryos? Draw a star at the beginning and end of the
sentence that answers the question.
15. What is the term for features that have different functions, but a similar structure? _______________
16. Read the story of the Peppered Moth. Explain how it supports Darwin’s Theory of Evolution.