Section 3: Evidence of Evolution

Unit 7: Evolution

Objectives

• Judge that conclusions are consistent and logical with experimental conditions.
• Know that both direct and indirect observations are used by scientists to study the natural world and universe.
• Interpret data from fossil records, anatomy and physiology, and DNA studies relevant to the theory of evolution.
• Discuss the implications of a universal genetic code for evolution.
• Describe how the degree of kinship between species can be inferred from the similarity in their DNA sequences.

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Warm-up:

• How can we tell if organisms have evolved or are currently evolving?

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Fossil Record

• Fossils: the preserved remains or traces of organisms that once lived on Earth.
• The fossil record is the collection of all fossils representing the history of life on Earth.
• It shows constant change over time.

Fossil Record

• Fossils form when an animal dies, sinks to the bottom of a body of water, and is buried in sediment. The sediment thickens and turns to stone around the skeleton. The bones are eventually dissolved and minerals can enter into the empty space and harden.

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Fossil Record

• Fossils that are found today are just a cast of the original bones. They no longer contain any cells or DNA of the original organism.
• Fossil formation is a very rare occurrence.
• Land animals/plants need to be near water in order to become fossilized.
• Soft tissue decomposes too fast to be fossilized.

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Fossil Record

• Fossils provide evidence that there were organisms on Earth that are no longer living.
• They also show how living things were different from the organisms that are currently alive.

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Fossil Record

• Fossils give clues about the evolutionary history of an organism.

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Fossil Record

• When fossils are found, clues can be used to help determine their age.
• Relative dating: the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age.

Fossil Record

• Stratigraphic dating is a technique of determining which fossils are older based on their positioning in the layers of earth.
• However, the earth does not remain constant. It is always changing, which could affect how the fossils are interpreted.

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Fossil Record

• Absolute dating: is the process of determining an age on a specified time scale in archaeology and geology.
• Radiometric Dating: a technique to determine the absolute age of fossils by evaluating the amounts of certain radioactive isotopes present.
• Carbon-14: takes 5,730 years for half of the sample to decay. (Good for fossils between 100-70,000 years old)
• Uranium-238: half-life 4.5 billion years (10 mil - 4.6 bil years)

Fossil Record

• Absolute dating allows scientists to determine the exact age of fossils with about 1% error.

Fossil Record

• Using all of the evidence gathered to date, we can view life’s history on the geological timeline.

Check for Understanding

Which layer would most likely contain the oldest fossils?

Biogeography

• Biogeography: the study of distribution patterns of living organisms around the world.
• Some species are missing from environments that would suit them. This suggests that they evolved only in certain locations and were not placed wherever they could survive.
• Ex: Polar bears live in the arctic, but not in Antarctica.

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Biogeography

• Species that are geographically closer to each other have closer relationships than species that inhabit similar environments.
• Ex: The sugar glider is more closely related to the kangaroo than it is to the gray squirrel.

Australia

Australia

North America

Biogeography

• Very distantly related species develop similarities in similar environments.

Pangolin

Armadillo

Comparative Anatomy

• Divergent Evolution: the accumulation of differences between groups that can lead to the formation of new species.

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Comparative Anatomy

• Homologous structures serve as evidence of divergent evolution.
• Homologous Structure: a physical characteristic in different organisms that is similar because it was inherited from a common ancestor.

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Comparative Anatomy

• Embryology: the branch of zoology studying the early development of living things.

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Comparative Anatomy

• Comparing the developmental stages of different animals provides evidence that different species shared common ancestors.

Comparative Anatomy

• When examining species that are currently alive, structures have been found that do not seem to have any valuable function.
• However, these structures do provide clues to the evolutionary past of a species.
• Vestigial Structure: a physical characteristic in organisms that appears to have lost its original function as a species has changed over time.

Comparative Anatomy

• Convergent Evolution: a process of natural selection in which features of organisms not closely related come to resemble each other as a consequence of similar selective forces.
• While the organisms may be similar, they can never become the same species.

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Comparative Anatomy

• Convergent evolution results in the formation of structures and traits that are similar in species that aren’t closely related.
• Analogous Structure: a physical structure, present in multiple species, that is similar in function but different in form and inheritances.

A: Homologous structures result from divergent evolution.

B: Analogous structures result from convergent evolution.

Check for Understanding

Are these examples of homologous structures or analogous structures? Do they result from convergent or divergent evolution?

Molecular Biology

• With advances in technology and a greater understanding of genetics, molecular biology and DNA also provide a great amount of evidence in support of evolution.
• All living things use nucleic acids (DNA or RNA) to store genetic information.
• DNA and RNA are composed of the same molecules in all living things.

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Molecular Biology

• Many organisms have the same or similar genes that produce the same or similar proteins.
• Similarities in DNA can be used to determine how closely related two organisms are.
• Organisms that are more closely related have more genetic similarities.

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Lab and Field Experiments

• Until recently, people thought evolution was too slow a process to be observed in action.
• By choosing species with short life spans and designing careful experiments, it is possible to observe evolution as it is happening.

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