The Theory of Evolution Charles Darwin Evidence for evolution Mechanisms for evolution Natural selection Speciation Evidence of evolution Structural adaptations Mimicry Camouflage Physiological adaptations Change in a metabolic process Fossils Anatomy Homologous structures Analogous structures Vestigial structure Embryos Biochemistry The Theory of Evolution Charles Darwin Evidence for evolution Mechanisms for evolution Natural selection Speciation Observation: Limits are placed on population expansion by limited environmental resources Conclusion: Therefore not all organisms will survive to adulthood and reproduce therefore there must be a struggle for existence (Source: observations reinforced by Malthus) 1
Observations: Not all members of a species are alike (variation) Parents often pass their individual variations on to their offspring Conclusions: individuals featuring favorable variations will enjoy a competitive advantage over others they will survive in proportionately greater numbers and will produce offspring in increasingly greater numbers (Source: Animal breeders, taxonomists) There is differential reproduction and differential survival, i.e., natural selection (Author of inference: Darwin) Conclusion: Through the action of natural selection over many generations a species could evolve (Author of inference: Darwin) 2
Both Darwin and Wallace knew: the principle cause of natural selection is the environment Biston betularia (a) The dark form is more visible on the light, lichencovered tree. (b) On trees darkened by pollution, the lighter form is more visible. Variation in the peppered moth. Understanding Physical Anthropology and Archaeology, 9th ed., p. 29 But look at them without color vision. 3
The moths satisfy all four conditions for natural selection: they reproduce; their color pattern is inherited; there is variation in their color patterns; the different forms have different fitness. Mechanisms for evolution Do populations or individuals evolve? Populations What is a gene pool? All of the alleles in a population How can the gene pool change? Mutation Genetic drift Gene flow Would these things effect a large population or a small population more? Contrasting ideas about the mechanism of evolution. (a)according to Lamarck s theory (b) According to the Darwin-Wallace Understanding Physical Anthropology and Archaeology, 9th ed., p. 24 4
The Theory of Evolution Charles Darwin Evidence for evolution Mechanisms for evolution Natural selection Speciation What is speciation? Geographic isolation Reproductive isolation Geographic isolation Reproductive isolation Gradualism Punctuated equilibrium What is speciation? 5
What is speciation? Geographic isolation Reproductive isolation Gradualism Punctuated equilibrium Divergent evolution Adaptive radiation Convergent evolution Adaptive radiation an example of divergent evolution http://www.vanderbilt.edu/ans/english/clayton/galapago_finches.gif Convergent evolution what is an example? Problem What is the source of individual variation? lack of knowledge of modern genetics 6
Neither Darwin nor Wallace knew: the source of individual variation = genetics (inherited characteristics) Problem: If natural selection only weeds out what already exists, how can it produce anything new? Didn t know then because of lack of knowledge of mutation and sexual recombination from modern genetics Mechanisms for evolution Do populations or individuals evolve? What is a gene pool? How can the gene pool change? Mutation Genetic drift Gene flow Would these things effect a large population or a small population more? 7