Lecture 3. Evolution

Alfred Russel Wallace

“On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life” (1859)

Darwin’s Theory of Evolution Variation: There is variation among the individuals of most natural populations Inheritance: Some of that variation is inherited Competition: Populations tend to produce more offspring than the evolution can support Survival of the Fittest: Those individuals whose traits best adapt them to the environment will survive better and leave more offspring than those with less adaptive traits

Key forces which influence the evolution of species Environmental changes (e.g. geographic isolation of marsupials) Random factors (e.g. Genetic drift due to the founder effect)

CONVERGENT EVOLUTION Different species come to resemble each other due to the similarities in their habitats (ecological niches) * *

DIVERGENT EVOLUTION Increasing separation between related species due to the process of adaptive radiation * *

Analogous Homologous structures structures Structures that are similar in the way they look because they share similar function but evolved independently Structures that share the same origin (e.g. ancestral mammalian limb) but serve different function in different species

Analogous structure

VESTIGIAL ORGAN: no longer useful but still retained A vestigial structure in the skeleton of a baleen whale. The pelvic bones have no apparent function.

Common Fallacies about Evolution Progressivism Fallacy Teleology Fallacy (Purposivism Fallacy) <-HUMAN

How Fast is Evolution? Gradualism Hypothesis (Charles Darwin) Punctuated Equilibrium Hypothesis (Stephen Jay Gould and Niles Eldrege)

DARWIN’S FINCHES

Natural Selection in Action *

Daphne Major Normal yearDrought year

The story of the ground finch Medium Ground Finch (Geospiza fortis) Seed Eater Every year on Daphne all the birds are caught and measured Their food size is measured Ground finch

Beak Depth is Inherited

Figure Drought Seed size and hardness Year What happened to the food ?

Drought What happened to the finches? Beak size Year

Finch Summary Beak depth is a trait that responds to changing environmental conditions Beaks appear to be an adaptation for feeding Evolution is a process-continually in operation –Sometimes measurable in real time

Darwin’s Theory of Evolution Variation Inheritance Competition Survival of the Fittest