Evolution Connection #4: Cladistics and Evolution by Natural SelectionIn this unit we discussed the role of DNA in cells. We have talked a good deal about how proteins are made, and their many functions within an organism. Our next evolution connection will look at the theory of evolution by natural selection; we will learn how species can change over time, and how new species can come to be. As you go through this evolution connection, keep in mind that mutations in DNA and their resulting changes in protein structure are responsible for all the variation we see in the organisms of Earth!

Part I: Evidence for Evolution

Look for the following sections, each of which examines a different type of evidence for evolution: Structural Homologies Fossil Evidence Observational Evidence (we can observe changing populations) Molecular Evidence

Go to http://evolution.berkeley.edu/evolibrary/article/evo_01Start with “Patterns”. Explore the following pages in this module: Homologies and Analogies.

1. What are homologies? What are analogies? Which one comes from a common ancestor?

2. Bird and bat wings are analogous. Why did similar structures evolve separately in these two groups?

Anthro.palomar.edu

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Video: “Who Was Charles Darwin?” http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

3. What characteristics made Darwin especially well suited for science?

4. What did Darwin see and do on his 5-year voyage aboard the Beagle?

5. What new idea did Charles Darwin introduce to science? How did it challenge the current understanding of biodiversity?

Fossil EvidenceVideo: “How Do We Know Evolution Happens?”http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

6. How do fossils give us a picture of change over time?

7. What distinguishing feature of the fossil Pakicetus skull identified it as related to a whale? Why was this surprising?

8. Why do scientists seek fossils that are intermediate in form and time between modern forms and their probable earliest ancestors?

Interactive: Transitional Fossilshttp://www.pbs.org/wgbh/nova/evolution/fossil-evidence.html

9. This resource describes 5 important transitional fossils that have helped our understanding of evolutionary history. Fill in the table below with information about each one.

Fossils Represents a link between what two modern groups?

What physical structure(s) were modified from earlier ancestors?

How long ago?

Tiktaalik rosae

Thrinaxodon

ArchaeopteryxAmbulocetus natansAustralopithecus afarensis

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We Can Observe Changing PopulationsVideo: How Does Evolution Really Work? http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

10. What are the four components of natural selection?

A.

B.

C.

D.

11. What determines an individual hummingbird’s beak length?

12. What factors in the environment might select for beak length and shape within hummingbird populations?

13. How can hummingbird DNA help Dr. Schneider determine the evolutionary history of hummingbirds?

Molecular Evidence

Interactive: Darwin’s Predictionshttp://www.pbs.org/wgbh/nova/evolution/darwins-predictions.htmlMany scientific discoveries have supported Charles Darwin’s original theory of evolution by natural selection. This interactive examines 12 predictions Darwin made, and discusses supporting discoveries that have been made since Darwin’s publication of his book.

14. For each prediction, briefly describe the supporting evidence.Evolution happens

Evolution happens through natural selectionEvolution by natural selection must have a mechanismThe mechanism is natural, not supernatural.

In-class activity: The Grant Finch Study Data

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Embryology is "the strongest single class of facts in favor of change of forms."Sexual selection also drives evolution.

All animals, including humans, descend from a common ancestor.Humans evolved from an ape-like ancestor.Modern humans arose in Africa.

The Earth is at least several hundred million years old.Gaps in the fossil record will be filled in with key transitional fossils.An insect with a foot-long tongue must exist to pollinate this orchid.

Part III: Mechanisms of Evolution

Go to http://evolution.berkeley.edu/evolibrary/article/evo_01Click on “Mechanisms”. You will progress through all pages of this module.

15. Briefly describe each of the following mechanisms of evolution:

A. Mutation:

B. Migration:

C. Genetic Drift:

D. Natural Selection:

16. What are the three sources of genetic variation in sexually reproducing populations?

In-class activity: Birds, beaks, and natural selection.

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17. List three examples of behaviors that have evolved by natural selection.

18. Why do organisms do things that don’t necessarily increase their chance for survival: peacocks grow giant tails, penguins care for their young, and lobsters produce thousands of offspring.

19. Define sexual selection.

20. How does artificial selection support Darwin’s theory?

21. List three examples of adaptations that have arisen by natural selection.

22. What are vestigial structures? Give an example of a vestigial structure.

Flashy Fishhttp://www.pbs.org/wgbh/evolution/educators/lessons/lesson4/act2.html

23. Fill in the chart below. Pros Cons

Drab colors

Flashy colors

24. In which pool does each survive best? Why?

25. Why does it make sense for females to choose the brightest males? (Hint: after running your simulation you will be looking at the results page. Click on “read summary” under the results window.)

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In-Class Activity 1: Grant Finch Study Data

Natural Selection in Real Time

"When we made the comparison between the size of the offspring generation and the population before selection, we found a measured, evolutionary response had taken place and it was almost identical to what we had predicted."-Peter Grant

Darwin thought that evolution took place over hundreds or thousands of years and was impossible to witness in a human lifetime. Peter and Rosemary Grant have seen evolution happen over the course of just two years.

The Grants study the evolution of Darwin's finches on the Galapagos Islands. The birds have been named for Darwin, in part, because he later theorized that the 13 distinct species were all descendants of a common ancestor. Each species eats a different type of food and has unique characteristics developed through evolution. For example, the cactus finch has a long beak that reaches into blossoms, the ground finch has a short beak adapted for eating seeds buried under the soil, and the tree finch has a parrot-shaped beak suited for stripping bark to find insects.

The Grants have focused their research on the medium ground finch, Geospiza fortis, on the small island of Daphne Major. Daphne Major serves as an ideal site for research because the finches have few predators or competitors. (The only other finch on the island is the cactus finch.) The major factor influencing survival of the medium ground finch is the weather, and thus the availability of food. The medium ground finch has a stubby beak and eats mostly seeds. Medium ground finches are variable in size and shape, which makes them a good subject for a study of evolution.

The first event that the Grants saw affect the food supply was a drought that occurred in 1977. For 551 days the islands received no rain. Plants withered and finches grew hungry. The tiny seeds the medium ground finches were accustomed to eating grew scarce. Medium ground finches with larger beaks could take advantage of alternate food sources because they could crack open larger seeds. The smaller-beaked birds couldn't do this, so they died of starvation.

In 1978 the Grants returned to Daphne Major to document the effect of the drought on the next generation of medium ground finches. They measured the offspring and compared their beak size to that of the previous (pre-drought) generations. They found the offsprings' beaks to be 3 to 4% larger than their grandparents'. The Grants had documented natural selection in action.

While beak size is clearly related to feeding strategies, it is also related to reproduction. Female finches tend to mate with males that have the same size beaks. These factors together can add to the development of new species.

The Grants return each year to Daphne Major to observe and measure finches. They have been collecting data on the finches for over 25 years and have witnessed natural selection operating in different ways under different circumstances.

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In-class Activity 2: Modeling Natural Selection

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