Evolution and Natural Selection

Testable Hypotheses Use if…then… logic Collect data Reject the null hypothesis Support the hypothesis Devise another test, and another, and another! Proximate: overexpress avpr1a gene in polygynous males Ultimate: Allow females to select mates, find they would choose more than 1

Charles Darwin, 1859, The Origin of the Species

Darwinian Theory Evolutionary change is inevitable if: Variation exists, such that members of a species differ in some of their characteristics Heredity exists, such that parents are able to pass on some of their distinctive characteristics to their offspring There are differences in reproductive success, such that some individuals have more surviving offspring than others in their population, thanks to their distinctive characteristics.

Natural Selection Relies on transmission of genes, small segments of DNA that encode proteins: heredity Genes exist in more than one form, or allele, giving rise to variation If a given allele allows for greater reproductive success, it will be passed on to more offspring, and eventually become more common in the population

Prairie Vole AVPR1a gene polymorphisms

Discussion Question If you wanted to invent the term “genetic success” for use in evolutionary studies based on natural selection theory, what would your definition be?

Natural selection in the lab: Carol Lynch Natural selection in the lab: Carol Lynch. how much cotton mice collect to make their nests is a natural variation in the population. In each generation, big nesters were bred with big nesters, and so on.

Rapid Evolution of beak size

Infanticide Understanding the evolution of puzzling, seemingly maladaptive behaviors. Form groups of a male, several females, and their offspring. Males exchange groups with disastrous consequences.

Infanticide 1. Leave the mothers no option but to mate with the killer male-Darwinian theory With no infant, the mother resumes cycling sooner, become impregnated sooner, more babies with killer male 2. Social pathology due to overcrowding Maladaptive, aggressive behavior by males 3. Population regulation Adaptive killing preserves food supplies, other resources Three hypotheses

Group Selection Groups that lacked the ability to keep the population in harmony with the available resources went extinct, while those with infanticidal males were able to balance and thus persist. Beneficiary of group selection is not the male himself, but the entire group. Selection acting on individual differences usually has a stronger effect than group selection Proposed by V.C. Wynne-Edwards in 1962. Generally acknowledged, but natural selection is preferred theory. George C. Williams’ Adaptation and Natural Selection in 1966 challenged Wynne-Edwards’ theory.

Discussion Question Lemmings: Many leave their homes and travel during conditions of population crowding, often dying in streams and lakes. One hypothesis states that the lemmings are committing suicide, so that those remaining can use the limited resources and survive to prevent extinction of the species. What theory was used to propose this hyothesis? How could you test it? (See next)