15-2 Theories of Evolution

1. 15-2 Theories of Evolution • Evolution: An orderly succession of changes. • Lamarck’s Explanation: • Proposed a unifying hypothesis of species modification – • Similar species descended from a common ancestor. • His explanation – acquired traits were passed down to offspring. • Note: An acquired trait is one that is not determined by genes! It arises during an organism’s lifetime as a result of experience or behavior.

3. **Even though Lamarck’s hypothesis was criticized, his work is important in that it clearly states that organisms change over time. The Beginning of Modern Evolutionary Thought Charles Darwin and Alfred Wallace independently proposed that species were modified by natural selection. Natural Selection: organisms best suited to their environment reproduce more successfully than other organisms. Thus, those with favorable traits will make up future populations.

5. Charles Darwin 1809-1882 Sailed on the Beagle for a 5-year map making and collecting expedition to South America and the South Pacific. Darwin acted as the ship’s naturalist and was inspired by: turtles Harriet galapagos Uniformitarianism – geological structure of the Earth resulted from cycles of observable processes that that have operated continuously through time. Ex.: Silt is deposited in modern rivers just as it was in ancient ones. Land has changed in the past, so it will continue to change very slowly. So organisms that lived in these areas would have to adapt to the changes. uniforitarianism

6. It looks like all these birds found on the Galapagos islands descended from one bird originally from South America. See p. 285 map.

7. The Origin of Species - Book published with Darwin’s work. The naturalist, Alfred Wallace had a similar hypothesis. Darwin’s Theories Descent with Modification: newer forms of life are the modified descendants of older species. See p. 287, figure 15-6. Modification by Natural Selection: The environment limits population growth by increasing death rate or decreasing reproduction rate. Those that have an adaptive advantage survive to pass on their fitness. Theories

8. Section 15-2 Review What is an acquired characteristic? Do they change the genotype of an organism? How did Lyell’s book, Principles of Geology, help Darwin see that natural selection over many generations could explain species modification? Why is Darwin’s publication still considered so important? Do Darwin’s theories of evolution by natural selection contradict the principles of biogeography? Why/why not? What did Darwin think limits the growth of populations?