2) early evolutionary theory & darwin

great chain of being

• fixed, ranked hierarchy of all life; species unchanging

• no extinction; “plentitude” (everything that can exist does)

• world in stasis, humans near top

natural theology

• science & religion intertwined

• world is orderly and purposeful; physical expression of god’s design

archbishop james ussher

calculated earth created 4004 BC from biblical genealogies

nicolaus copernicus

heliocentric model displaced earth/humans from center of the universe

john ray

• coined “species”

• interbreeding criterion (fertile offspring = same species)

carolus linnaeus

• father of taxonomy; systema naturae

• binomial nomenclature (genus + species)

• classification originally aligned with GCB

comte de buffon

• species should be classified by features and behaviors/environment

• proposed common descent and earth older than 6000 years (uniformitarianism)

• recognized organic change, but lacked mechanism

dodo bird

proved extinction with the arrival of humans, directly undermined GCB

georges cuvier

• father of paleontology, documented extinctions of dinosaurs

• catastrophism: sudden natural events caused faunal turnover

james hutton

• father of geology

• uniformitarianism, past processes = present processes

• gradualism: slow accumulation = earth extremely old

charles lyell

• built on hutton; principles of geology

• change is the only constant

jean-baptiste lamarck

• first full evolutionary theory

• inheritance of acquired characteristics (use/disuse → passed to offspring)

• believed organisms “strived for perfection”

• wrong mechanism, but important for proposing environment-driven change

thomas malthus

• populations grow faster than resources → struggle for existence

• influenced darwin’s idea of competition and survival

darwin: background and influences

• naturalist on HMS beagle; collected fossils, specimens

• read lyell’s geology → earth old, change gradual

• influenced by:

  • lyell (deep time + gradual change)

  • malthus (competition)

  • breeders (inheritance + variation)

  • cuvier (knowledge of extinction)

• observed galapagos finches/tortoises → geographic variation inconsistent with GCB

darwin’s theory of natural selection

core observations:

• variation exists naturally within population

• some variation is heritable

• more offspring produced than can survive (competition)

• individuals with advantageous traits survive + reproduce more

conclusion:

• favorable traits increase in frequency over generations

• natural selection = differential survival + reproduction

darwin’s postulates

• populations overproduce → struggle for existence

• variation exists and affects fitness

• variation is heritable

peppered moth example

• pre ir: light moths camouflaged on lichen-covered trees

• post ir: soot killed lichens, trees dark → dark moths favored

• industrial melanism = natural selection driven by environmental change

giraffe example

lamarck: neck stretched during life span → trait acquired → inherited

darwin: individuals with longer necks had advantage and reproduced more

publication of darwin’s work

• developed ideas for 21 years; illness, social/religious concerns delayed publication

• wallace independently reached same conclusion → joint 1858 paper

• origin of species (1859) published, but mechanism of heredity still unknown