Evolution

What came first? Jean-Baptiste Lamarck (1744–1829) “Transmutation” incorporated two ideas into his theory of evolution, in his day considered to be generally true: Use and disuse – Individuals lose characteristics they do not require (or use) and develop characteristics that are useful. Inheritance of acquired traits – Individuals inherit the traits of their ancestors.

Examples of Lamarckism Giraffes stretching their necks to reach leaves high in trees, strengthen and gradually lengthen their necks. These giraffes have offspring with slightly longer necks (also known as "soft inheritance"). A blacksmith Through his work, strengthens the muscles in his arms. His sons will have similar muscular development when they mature.

What came next? Charles Darwin Naturalist Biogeography Focused on finches that lived on the Galapagos Islands Several species – different islands Similar to each other and a species from the mainland Hypothesis: Different species of Galapagos finches descended from mainland species Island conditions varied/differed from mainland Developed new traits Enough changes occurred to qualify the finches as separate species

Proof? Darwin’s original theories BUT Today's scientists Only his observations of existing variation as evidence BUT Today's scientists Analyze DNA Confirmed these relationships Detailed studies support Darwin's hypotheses about the existence of different selective pressures on different islands.

Different patterns of evolution Convergent evolution species that are not closely related to each other independently evolve similar kinds of traits. E.G.: dragonflies, hawks, and bats all have wings. Wings = analogous structures.

Different patterns of evolution Divergent evolution trait held by a common ancestor evolves into different variations over time. E.G.: vertebrate limb - Whale flippers, frog forelimbs, and your own arms most likely evolved from the front flippers of an ancient jawless fish. Share a common evolutionary origin = homologous structures. Consequence of divergent evolution Speciation (the divergence of one species into two or more descendant species. )

4 forms of Speciation Allopatric speciation : Occurs when a population becomes separated into two entirely isolated subpopulations. Then - natural selection and genetic drift operate Different Genetic Outcomes E.G.? Peripatric speciation : Similar to allopatric speciation BUT occurs when a very small subpopulation becomes isolated from a much larger majority Because the isolated subpopulation is so small divergence happens rapidly due to the founder effect Small populations are more sensitive to genetic drift and natural selection acts on a small gene pool.

4 forms of Speciation Parapatric speciation: Small subpopulation remains within the habitat of an original population but enters a different niche. Effects other than physical separation prevent interbreeding between the two separated populations. Because one of the genetically isolated populations is so small, however, the founder effect can still play a role in speciation. Sympatric speciation: Rarest and most controversial form of speciation, occurs with no form of isolation (physical or otherwise) between two populations.

Parallel Evolution Sometimes difficult to distinguish from convergent evolution. Occurs when different species start with similar ancestral origins then evolve similar traits over time. Happens because the two different species experience similar kinds of environmental pressures adaptations E.G.: Plants several similar but distinct forms of leaf evolved in parallel and are evident today.

Coevolution Occurs when closely interacting species exert selective pressures on each other They evolve together in a kind of conversation of adaptations. E.G.: Predator-prey and host-parasite pairs. OR Hummingbirds and the flowers from which they seek nectar and unwittingly pollinate.  

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