1. Evolution: Darwin and Natural Selection “Why We Love Sugar” “Why We Love Sugar” “Why Our Brains Love Junk Food” “Why Our Brains Love Junk Food”

2. Darwin Darwin traveled around the world on the HMS Beagle. He went to collect plant and animal specimens.

3. Three Observations Species vary globally Species vary locally Species vary over time

4. Species Vary Globally Darwin found large, flightless, ground-dwelling birds called Rheas in South America. Rheas strongly resemble ostriches, but rheas only live in South America and ostriches live only in Africa. In Australia he found a similar bird, the Emu

5. Species Vary Locally Examples from the Galápagos Islands, about 1000 km off the Pacific coast of South America. These islands are close to one another, yet they have different ecological conditions.

6. Galapagos Tortoises Darwin saw differences among the giant land tortoises that inhabit the islands The neck structure and shape of the tortoises’ shells corresponds to different habitats.

7. Isabela Island Isabela Island has high peaks, is rainy, and has abundant vegetation that is close to the ground. Tortoise has dome- shaped shell and short neck.

8. Hood Island Hood Island, in contrast, is flat, dry, and has sparse vegetation. Tortoise has a long neck and a shell that is curved and open around the neck and legs

9. Species Vary Locally Darwin also noticed several types of small brown birds on the islands with beaks of different shapes- they were all finches!

10. Species Vary Over Time Darwin noticed that some fossils of extinct animals were similar to living species.

11. Which one of Darwin’s observations accounts for the fact that we find emus in Australia and Rheas in South America? A) Species vary globally B) Species vary locally C) Species vary over time

12. Which one of Darwin’s observations accounts for the fact that many animals living today have similar structures as animals found in the fossil record? A) Species vary globally B) Species vary locally C) Species vary over time

13. Which one of Darwin’s observations accounts for the different beak shape of the finches on the Galapagos Islands? A) Species vary globally B) Species vary locally C) Species vary over time

14. Darwin’s Question The observations being made in Geology caused Darwin to ask himself the question, –If Earth can change over time, can life change over time?

15. Natural Selection Tying together all of his observations, Darwin presented his idea of natural selection. Natural selection is the process by which organisms with variations most suited to their local environment survive and leave more offspring.

16. Natural Selection In natural selection, the environment determines fitness Fitness is measured by reproduction!

17. Natural Selection Well-adapted individuals survive and reproduce. From generation to generation, populations continue to change as they become better adapted, or as their environment changes.

18. Natural Selection Natural selection acts only on inherited traits because those are the only characteristics that parents can pass on to their offspring.

19. True or False: Evolutionary fitness is measured by amount of offspring produced. A) True B) False

20. Natural Selection is determined by: A) An organism’s ability to change its DNA B) An organism’s environment C) An organism’s mate

21. Natural Selection occurs on: A) Acquired traits B) Inherited traits

22. Natural Selection Natural selection occurs in any situation in which: –More individuals are born than can survive (the struggle for existence) –There is natural heritable variation (variation and adaptation) –There is variable fitness among individuals (survival of the fittest).

23. Natural Selection This hypothetical population of grasshoppers changes over time as a result of natural selection. Grasshoppers can lay more than 200 eggs at a time, but only a small fraction of these offspring survive to reproduce.

24. Natural Selection In this population of grasshoppers, heritable variation includes yellow and green body color. Green color is an adaptation: The green grasshoppers blend into their environment and so are less visible to predators.

25. Natural Selection Because their color serves as a camouflage adaptation, green grasshoppers have higher fitness and so survive and reproduce more often than yellow grasshoppers do.

26. Natural Selection Green grasshoppers become more common than yellow grasshoppers in this population over time.

27. What do you think would happen to the grasshopper population if there were several years of drought?

28. Each of the following is a condition necessary for natural selection to occur EXCEPT A) more offspring are born than can survive. B) population size is very large. C) fitness varies among individuals. D) there is heritable variation among members of the population.

29. Natural Selection Natural selection does not make organisms “better.” Adaptations don’t have to be perfect—just good enough to enable an organism to pass its genes to the next generation.

30. Natural Selection Natural selection also doesn’t move in a fixed direction. –There is no one, perfect way of doing something. Natural selection is simply a process that enables organisms to survive and reproduce in a local environment.

31. Natural Selection If local environmental conditions change, some traits that were once adaptive may no longer be useful, and different traits may become adaptive. If environmental conditions change faster than a species can adapt to those changes, the species may become extinct.

32. True or False: Natural Selection is directional. A) True B) False

33. True or False: Natural Selection is purposeful. A) True B) False

34. According to Darwin’s theory of natural selection, individuals who survive are the ones best adapted for their environment. Their survival is due to the According to Darwin’s theory of natural selection, individuals who survive are the ones best adapted for their environment. Their survival is due to the A) possession of adaptations developed through use. B) possession of inherited adaptations that maximize fitness. C) lack of competition within the species. D) choices made by plant and animal breeders.

35. The Big Brain Question: Explain the natural selection of humans due to their craving for sugar. (3 conditions: -more organisms born than could survive and reproduce; - variations: organisms that ate more or less sugar; - “more sugar” were more fit because…?)