Aristotle natural history essentialism species are fixed and unchanging concept of the “type”

Lamarck (1744-1829) 1802 Philosophie Zoologique tried to explain two phenomena: 1. diversity of form 2. trend of increasing complexity how is one species transformed into another ?

Lamarck, con’t mechanisms: 1. possible to increase complexity (forever) 1st notion of adaptation 2. organisms respond to environment inheritance of acquired characteristics consequences of environment and environmental change for the phenotype

Georges Cuvier (1769-1832) paleontology, comparative anatomy catastrophism: total destruction and replacement of flora/fauna species didn’t change; only non-essential features varied

Richard Owen Louis Agassiz

Charles Lyell species die out and are replaced how? - singly or all at once? why? - senescence? - environmental change?

Charles Darwin (1809-1882) Alfred Russell Wallace (1823-1913)

Charles Darwin ship’s naturalist on the HMS Beagle (1831-1836) -- fauna of Galapagos Islands: each island had similar physical conditions but distinct species of mockingbirds, finches, tortoises divergence in isolation from a common ancestor --fossils of Patagonia: similarity of fossil and living forms (e.g., armadillos) descent with modification

derivation of natural selection reproductive capacity and population increase (Malthus 1798 Essay on the principle of popn) population size is ~stable (most species) resources (food, space) are limited; “struggle for existence” no two individuals are identical much variation is heritable unequal survival; depends on genotype gradual changes over time in popns

1859 Origin of Species species are not fixed or constant 1. gradual descent with modification from a common ancestor (transformation and diversification) 2. modification via natural selection on individual variation Natural Selection = differential survival or reproduction of some individuals under current environmental conditions

Evolution by natural selection individuals within a species are variable some of the variations are passed to offspring (heritable) in every generation more offspring are produced than can survive Survival and reproduction are not random; individuals that survive +/or reproduce the best have the variations most favored in the current environment

AZT resistance is an example of evolution by Natural Selection 1. mutations by reverse transcriptase produce variant HIV molecules 2. mutants differ in enzyme function 3. differential survival in AZT environment resistance is costly (slow growth) 4. mutants are passed to ‘offspring’ of resistant genotypes effectiveness and speed of process -- rate of mutation (m ~1%/yr) -- strength of selection

Sewell Wright R. A. Fisher J. B. S. Haldane

natural selection in action: morphological evolution of Geospiza fortis Peter & Rosemary Grant and colleagues long-term study of G. fortis population on Daphne Is. two episodes of natural selection: 1976-77 severe drought 1983-84 extreme El Nino event

beak depth in G. fortis is highly variable

beak depth is highly heritable in this population

ENSO drought

normal vegetation on Daphne Is. drought 1976-77

fewer seeds harder seeds Tribulus

a decline in food results in a decline in finches

survival is not random; larger birds are more likely Evolutionary response of Geospiza fortis to selection in 1976-77 before selection next generation 1976 1978 Mean (SE) Mean (SE) D Weight (g) 16.06 (0.06) 17.13 (0.13) +1.07 Wing length (mm) 67.88 (0.10) 68.87 (0.20) +0.99 Tarsus length (mm) 19.08 (0.03) 19.29 (0.07) +0.21 Bill length (mm) 10.63 (0.03) 10.95 (0.06) +0.32 Bill depth (mm) 9.21 (0.03) 9.70 (0.06) +0.49 Bill width (mm) 8.58 (0.02) 8.83 (0.05) +0.25 Sample size 634 135 survival is not random; larger birds are more likely to survive than small birds

birds with deeper bills have higher survival

ENSO drought

normal wet season vegetation on Daphne Is. El Nino event 1983-84

the direction of selection is not constant

Natural selection acts on individuals, but the consequence is a change in the population phenotypic distribution Natural selection acts on phenotypes, but changes the genotypic distribution (without underlying genetic variation, evolution will not occur Each generation is the product of selection on their parents Natural selection acts on existing traits. New traits arise as a modification of old features and in combination with new mutations Natural selection is non-random, but not progressive