Lecture 1: Introduction to Evolution Evolution = change in allele frequencies in a population Great, is class over now? No (sigh), because the process & results are interesting & important to our understanding of biology

Questions in evolution WHY is life on earth diverse? (we’ll get to this later) HOW is life adapted ? (questions leading to more questions)

Adaptation Questions Are all traits adaptive? Are all adaptations perfect? Who/what benefits from adaptation? Where did all these questions come from?

BD : Before Darwin Orthodoxy – species as fixed, designed by God Bible = literal truth variation = imperfection BUT, even before Darwin this was questioned Idea of changeable/old Universe, allowed idea of changeable life on earth (geology & paleontology) Enlightenment – fossils: spontaneous generation, transmutation

Lamarck spp. change into new spp. over time Transformism:Acquired Characters: -no branchinge.g. Giraffe’s neck -no extinction So, Darwin had somewhere to start…

Darwin ( ) Noticed: geographic variation in very similar spp. Rejected orthodoxy – b/c did not explain adaptation Theory : why spp. change & why they are well designed for their lives Influences: –Malthus (population principle) –Lyell (continuous change vs. catastrophists) –Social influences (materialism)

Darwin’s conclusion ‘Struggle for existence’ only some survive Expect favourable variations to survive = Natural Selection Mechanism = most important aspect of theory Poor Alfred Russel Wallace – same conclusions on a much smaller budget –Co-presented the idea but Darwin is remembered because of The Origin of Species

Darwin’s Dangerous Idea The Origin of Species (1859) Theses: 1.Descent with Modification from Common Ancestors (Evolution) 2.Natural Selection is main agent of Evolution

Origin in a nutshell 1. Observed overproduction of offspring Many born – few survive to reproduce WHY? Limited resources – pop’ns limited in size Therefore STRUGGLE FOR EXISTENCE

2. Individuals vary If competition for resources then only favourable variants survive to reproduce 3. Most of the variation is inherited (e.g. domestic species – sexual repro:diversity) Favourable variants have more offspring & increase in frequency = Change in the population over time Plus lots about pigeons…

Deduction Descent with modification via natural selection Testable??? Predictions Fossil Record Comparative Anatomy Comparative Embryology Geographic Distribution Behaviour

Why Dangerous? Static  dynamic view of nature Creationism = implausible Platonic essentialism –variation = basic/neutral feature Refuted teleology & anthropocentrism Natural Selection –No goal –No consistent direction EVOLUTION  PROGRESS

Evolution is a bush not a ladder Fish Amphibians Birds Mammals Humans

Reception “Evolution” generally accepted but: 1.Viewed as progressive (towards a goal) 2.Natural selection rejected No theory of heredity (how characteristics passed on) Problem of uncrossable “gaps” in evolution Back to transmutation

The Modern Synthesis Mendelian genetics “rediscovered” in 1920s By 30s/40s widely accepted : 1.acquired characters not inherited 2.Continuous variation explained by Mendelian genetics (Fisher) 3.Theoretical works show N.S. can work with what is available in nature, nothing else required Speciation only requires N.S. not macromutation /acquired characters 4.Species are not morphotypes – dynamic concept

Tenets of Modern Synthesis Populations have variation from random, not adaptively directed, mutation & recombination Populations evolve through changes in gene frequency by drift, gene flow & N.S. Change is gradual because most genetic variants have slight effects on phenotype Diversification (speciation) is due to gradual reproductive isolation among populations Overtime, changes give rise to new taxa

Genetics…more important than Darwin? After Darwin, many accepted the idea of evolution as change in species over time BUT, much argument against NS Genetics forced the rejection of evolution as goal-oriented & the widespread acceptance of NS

Modern Evolutionary Biology Two principle goals: 1.Inferring history of evolution 2.Elucidating the mechanisms Modern evolutionary theory: Provide explanation for patterns of life in space & time & the processes by which these patterns arose