2. How Populations Evolve

3.  Jean-Baptiste Lamarck  Traits acquired during lifetime are inheritable  Charles Lyell  Geologic change is the steady accumulation of changes over a long period of time  Alfred Wallace  Contemporary of Charles Darwin  Conceived theory very similar to Darwin

4.  Attended Cambridge for religious studies  Biologist on HMS Beagle in 1831  Studied plants, animals, fossils  Influenced by Lyell’s geology ideas  Consulted with Wallace in 1850s

5.  1859—Published On the Origin of Species by Means of Natural Selection  Immediate controversy, continues today

6.  Members of a population vary in traits, traits are inheritable  Species produce more offspring than an environment can support  Individuals with traits that give them a better chance of survival & reproduction will tend to leave more offspring  Unequal production of offspring will cause these traits to increase in a population over generations

7.  Fossils  Older fossils deeper in strata of rocks  Older fossils show less variation  Older fossils show less complex features  Younger fossils show more variation and more complex features  Younger fossils have characteristics more like living organisms

8.  Biogeography  Study of geographical distribution of species  If species have similar characteristics but are in different locations, can infer that there was a common ancestor from which each evolved  Used with idea of continental drift

9.  Comparative Anatomy  Homologous structures—different functions but similar structure. Theorized to be due to common ancestry

10.  Comparative Anatomy  Vestigial structures—structures with little or no importance to organism. Theorized to be previously important organ that organisms evolved out of needing Some structures now seen to have uses and may not be “vestigial”

11.  Molecular Biology  Many organisms have similar DNA Comparable DNA to humans…. Other humans 99+% Chimpanzees—95-98% Fruit flies—60% Bananas—50% However, the similarities depend on how the analysis is performed (see this article or this one) this articlethis one

12.  New alleles and phenotypes originate by mutation  Most mutations are harmful or neutral  Some may confer some benefits  For examples, see this articlethis article  Mutations provide the variety in traits needed by Darwin’s description of natural selection  Beneficial mutations may increase survivability

13.  Genetic Drift—change in a gene pool due to chance  Smaller populations more quickly and strongly affected  Bottleneck Effect—Sudden and extreme event that leaves a small population  Flood, fire, earthquake, disease, etc.  Unlikely to have same genetic makeup of original population

14.  Any given trait has variations within a population  Height, hair color, tail length, beak thickness, immune response, etc.  Variations tend to follow a “bell curve”

15.  Stabilizing Selection  Favors intermediate phenotypes  Selects against extremes  Human birth weight Too large or too small increase risk for baby’s survival

16.  Directional Selection  Moves traits in direction of one phenotype extreme  Selects against other extreme  Coloration to allow better camoflague

17.  Disruptive Selection  Individuals at both extremes selected for  Intermediate forms selected against.  Galapagos finch beak size

18.  Organisms with certain physical traits are more likely than others to obtain mates  Some traits may compete with other factors of natural selection  Fighting for a mate may result in injury and death  Some physical traits (e.g. extremely large or long tails) may make survival difficult