Darwin ’ s Theory of Evolution

1. Darwin’s Theory of Evolution Adapted from a fellow AP Bio teacher

2. Who was Charles Darwin? • Charles Robert Darwin (February 12, 1809 – April 19, 1882) was a British naturalist who achieved lasting fame by convincing the scientific community of the occurrence of evolution and proposing the theory that this could be explained through natural and sexual selection.

3. I. What is Darwin’s theory of evolution?

4. Charles Darwin (1809 - 1882) was a British naturalist. • Theory = a well supported explanation of phenomena that have been observed in the natural world • Evolution = change over time (process by which modern organisms have descended from ancient organisms)

5. II. How did Darwin come up with his theory? • A. Voyage of the HMS Beagle (1831-1836)- Darwin set sail around the world as a naturalist to collect organisms and make observations

6. B. During his travels, Darwin made many observations about the variety of organisms that were alive and the variety found in the fossil record

7. C. Most influential stop – the Galápagos Islands. Here Darwin realized that habitat determined the physical characteristics of organisms. Example – Tortoises on different islands had differently shaped shells. Tortoises on Hood Island had a saddle-backed shell which allowed them to reach higher vegetation.

9. What is evolution? a. the increased reproductive success of the fittest individuals b. the diminished reproductive success of poorly adapted individuals c. the change in the inherited characteristics of a population over time d. the struggle for existence undergone by all living things

10. What is evolution? a. the increased reproductive success of the fittest individuals b. the diminished reproductive success of poorly adapted individuals c. the change in the inherited characteristics of a population over time d. the struggle for existence undergone by all living things

11. Example – Finches are found on every Galapagos Island. They are all similar but have differently shaped beaks. The shape of the beak reflects the habitat in which they live and the kind of food that they eat.

13. The observation by Darwin that finches of different species on the Galápagos Islands have many similar physical characteristics supports the conclusion that these finches a. have the ability to interbreed. b. acquired traits through use and disuse. c. all eat the same type of food. d. originated from a common ancestor.

14. The observation by Darwin that finches of different species on the Galápagos Islands have many similar physical characteristics supports the conclusion that these finches a. have the ability to interbreed. b. acquired traits through use and disuse. c. all eat the same type of food. d. originated from a common ancestor.

15. Finches’ beaks have evolved over time to be best suited to their function • For example, the finches who eat grubs have a thin extended beak to poke into holes in the ground and extract the grubs.

16. Finches who eat buds and fruit would be less successful at doing this, while their claw like beaks can grind down their food and thus give them a selective advantage in circumstances where buds are the only real food source for finches.

17. Animals do not have a choice! They do not get to choose what characteristics they have and usually do not get to choose what type of environment they live in. Change happens over a loooong time as the environment exerts selective pressures on organisms.

18. Among the birds that lived in arid environments, the ones with beaks better suited for eating cactus got more food and survived to reproduce.  • Those who could not find food in that environment (that did not have advantageous adaptations) did not survive to pass on their genes) • Similarly, those with beak shapes that were better suited to getting nectar from flowers survived in environments with a lot of flowers. etc. etc. etc.

19. D. On his journey home, Darwin spent time reviewing his findings. He had collected thousands of specimens, fossils, pages of notes

20. Descent with Modification • Darwin came to understand that any population consists of individuals that are all slightly different from one another.  • Those individuals with a variation that gives them an advantage in staying alive long enough to successfully reproduce are the ones that pass on their genesmore frequently to the next generation.   • Subsequently, their traits become more common and the population evolves. 

21. After Darwin returned to England, he spent the next 25 years reviewing his data and observations! • In 1859 he published his book, The Origin of Species, which proposed his theory of evolution by natural selection.

22. What is Evolution by Natural Selection? A. Natural selection says that if: • There are organisms that reproduce, • Whose offspring inherit traits from their parents, • There is variation, and • The environment limits the size of natural populations (limited food and resources), • Then those members of the population with poorly adapted traits (as determined by the environment) will die out or reproduce less, and • Those members with better adapted traits (as determined by the environment) will survive to reproduce more

26. According to Darwin's theory of natural selection, individuals who survive are most likely the ones best adapted to exist in their environment. Their survival is due to the a. possession of structures developed through use. b. possession of adaptations that maximize fitness. c. lack of competition within the species. d. ability to change their genotype.

27. According to Darwin's theory of natural selection, individuals who survive are most likely the ones best adapted to exist in their environment. Their survival is due to the a. possession of structures developed through use. b. possession of adaptations that maximize fitness. c. lack of competition within the species. d. ability to change their genotype.