Evolution History of evolutionary theory Sources of variation

Evolution

§ History of evolutionary theory § Sources of variation § Agents of change § Population controls

Pre 1700’s § Aristotle and Plato - different forms of life evolve from one another § Christians - Creation as in Genesis

Cuvier § Theory of Catastrophism § Local catastrophies caused extinctions § Surrounding species repopulated areas after catastrophies

Lamarck § Inheritance of acquired characteristics

Darwin § Studied theology and natural history § Naturalist on Beagle survey ship § Wrote Origin of The Species

Voyage of the Beagle

Galapagus Islands

Darwin’s Theories § All organisms related through a common ancestor § Species do not remain unchanged over time

Darwin’s Reasons § High reproductive rate leads to continual struggle for survival of offspring § Variation of characteristics mean some are better adapted § Those with favourable variations survive to reproduce § Each successive generation is better adapted § Eventually a new species will evolve

Sources of Variation § Mutations produce new alleles § Sexual recombination and crossing over at meiosis creates variation of offspring

Agents of change § § § § Natural selection Genetic drift Founder effect Bottleneck effect Gene migration Mutations Non-random mating

Natural Selection § Environment acts on phenotype § Stabilising selection § Directional selection § Disruptive selection

Stabilizing selection § Maintains population in a stable form § Favours the average

Directional selection § Favours phenotype at one extreme § Leads to shift in average variation

Disruptive selection § Favours both extremes

Disruptive selection

Genetic Drift § In small populations § Causes change fluctuations in gene pool § A change in the gene pool of a small population due to chance

Founder Effect § Genetic drift in a new colony § Only a few founding members of a population

Bottleneck Effect § Disaster reduces population to a few survivors § Random deaths § Some alleles lost from gene pool, others over represented

Gene Miration § Immigration § emmigration

mutations § Substitute 1 allele for another

Non-Random Mating § Mate near-by - often inbreed causing alleles to become homozygous § Unfavourable genes enhanced

Increase genetic variability Mutations immigration Decrease genetic variability Natural selection Emigration Non-random mating Genetic drift

Evidence for Evolution § § § Biogeography Fossil record Comparative anatomy Comparative embryology Molecular biology domestication

Biogeography § Geologically separated areas inhabited by organisms that are ecologically similar § Endemic species on islands

Fossil Record § Non-living object from the ground that indicates former presence of a living thing

Fossil types § § § Caste Mould Deep-frozen In amber Tar lakes Turn to stone

Cast

Bone to Stone

Comparative Anatomy § Homologous structures § Similar characteristics from common ancestry

Analogous Structures § Same function § Different ancestry

Vestigial Organs § Organs that are reduced or lost

Comparative Embryology § Early embryonic stages of all vertebrates very similar

Molecular Biology § Similar species have only small differences in DNA and proteins