Evolution Review Chapters 22-24

History of Evolution? Hutton: gradualism Malthus: population studies Lamarck: theory of acquired characteristics (crop a dog’s ears…) Lyell: geological studies Then came…. Darwin (and Wallace)

Darwin Descent with modification: all organisms descended from common ancestors… but have experienced small changes The history of life is like a tree, with each branch representing a lineage of some organism

Natural Selection Natural selection is differential reproductive success Natural selection occurs through an interaction between environment and organisms with genetic variations The product of natural selection is adaptation of populations to environment

Artificial selection Some outside force (humans) choose organisms with certain characteristics Breeding animals for certain traits

Evidence of Evolution Biogeography: geographical distribution of species Fossil record: dating fossils, making comparisons Comparative anatomy: homologous structures (bat wing, bird wing, human arm, whale flipper)

Continued…. Vestigial structures: no or reduced function (appendix) remains from earlier ancestor who did use it Comparative embryology: many organisms go through similar stages of development pointing to common ancestor Molecular biology: DNA evidence shows species relatedness

Population genetics Emphasizes the extensive genetic variation within populations Population: same species, same place… capable of reproducing Gene pool: all the genes in a population

Hardy-Weinberg Frequencies of alleles in a population remain constant over time Meiosis and genetic recombination have no net effect on frequency of alleles

Conditions Large population No gene flow No mutations Random mating No natural selection Describes idealized populations to allow for the study of real populations

Genetic drift Changes in gene pool of a small population due to random chance Bottleneck effect: a disaster wipes out most of population unselectively… survivors have limited genetic diversity and population goes through bottleneck Founder effect: small group colonizes new area, whole population is only as diverse as founders

Types of Selection Stabilizing: acts against extreme phenotypes Directional: selects one extreme or other Diversifying: selects both extremes Sexual: choose mates based on characteristics like size, color, behavior, etc.

Natural Selection revisited It cannot make perfect organisms It can only work with what genetic diversity is present Not all evolution is adaptive, meaning some evolution is truly pointless…

Reproductive isolation… keeps species distinct Prezygotic: Habitat isolation Behavioral isolation Temporal isolation Mechanical isolation Gametic isolation Postzygotic: Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown – when the hybrid offspring mate, it does not work!

Speciation Speciation: the creation of a new species Allopatric speciation: “other homeland” a geographical barrier physically isolates populations until they become new species Sympatric speciation: new species emerge within a population due to chromosomal changes or nonrandom mating

Models of evolutionary change Gradualism: evolution is the result of tiny changes accumulating over long periods of time (see intermediate species) Punctuated equilibrium: evolution occurs rapidly with big changes (no intermediate species seen)