15 3 Darwin Presents His Case Darwin Presents

15. 3 Darwin Presents His Case

Darwin Presents His Case • The specimens Darwin brought back had the scientific community in a buzz • Learned that Galapagos species are found nowhere else in the world • They looked similar to South American mainland species but were clearly different

Darwin’s Book • Published his ideas about species diversity and evolution in On the Origin of Species • Proposed a mechanism for evolution called natural selection • Many agreed with Darwin while others strongly opposed him

Natural Variation • Scientists used to believe species were perfect and unchanging • Darwin argued natural variation (differences among species) is found in all types of organisms – Some cows give more milk – Some plants give larger fruit

Artificial Selection • Darwin also studied English farmers and breeders • Used selective breeding to breed the “best” individuals – Largest hogs, fastest horses • Darwin called this artificial selection • Still used today!

Evolution by Natural Selection • Darwin believed that evolution occurred through natural selection • Natural selection = the process by which only the organisms best adapted to their environment will survive and reproduce • 3 main parts to natural selection

1. The Struggle for Existence • There are more living things than resources • Results in competition • Competition = the struggle among living things to get their needs for life

2. Survival of the Fittest • Individuals that are better suited to their environments survive (high fitness) • Individuals not suited to their environment will die (low fitness) • Fitness – the ability of an individual to survive and reproduce in its environment – Is a result of adaptations

2. Survival of the Fittest • Adaptation – any inherited characteristic that increases an organism’s chance for survival – Long necks in giraffes – Long toes / webbed feet in birds – Coloring / Camouflage

3. Descent with Modification • Each living species has descended, with changes, from other species over time • Implies all organisms are related to one another – Known as common descent

Evidence for Evolution • Fossil Evidence – When living things from the past are compared to living things today, we can see that change has occurred

Evidence for Evolution Beaver NORTH AMERICA Muskrat Beaver and Muskrat Coypu Capybara SOUTH AMERICA Coypu and Capybara • Geographic distribution of living things – Species are located in different parts of the world but share similarities – Beavers and capybara are similar – Muskrat and coypu are similar

Evidence for Evolution • Homologous body structures – Limbs (arms, wings, legs, flippers) have different form and function but are constructed from the same bones Turtle Alligator Typical primitive fish Bird Mammals

Evidence for Evolution • Vestigial structures – Body parts that no longer have functions – i. e. Pink lump in corner of eye • Remnant of a third eyelid • Frogs and turtles have third eyelid to see underwater – Appendix • In many mammals the appendix is used to help digest food

Evidence for Evolution • Embryology – Studying embryo development to look for similarities and differences