Last day… overview of what the course will cover, started discussing historical development of

evolutionary thinking

- idea of evolution had been debated, but generally rejected

Buffon Erasmus Darwin Saint Hilaire Lamarck

Charles Darwin

- provided evidence that evolution had occurred- first to develop a theory to explain how & why

evolution happens

Glyptodon

- left him last day on voyage of the Beagle (1832-36)

4 spp. ofmockingbirdsfrom Galapagos

What patterns of distribution would be expected if species are independently created (as opposed to what is expected if species are related by descent from a common ancestors)?

a) very similar species will be expected in similar habitatseven if on different continents

b) species in very different habitats will be very different,even if the habitats are geographically close

c) different species will be found on opposite sides of geographic barriers, even if the habitats are similar

d) endemic species on islands will be closely similar to those of the nearest continent

e) species will be found in environments that they are welladapted to

- influence of geological theories Lyell: Uniformitarianism: geological patterns created by presently observable forces, ancient history of the earth

Charles Lyell: 1797-1875

Started notebook (1837) to record ideas Many facts suggested evolution, but needed a theory...

- must produce change

- must account for adaptation

- must explain speciation

Inspiration from Thomas Robert Malthus (1798)

- population growth will always tend to outrun food supply

- immediately suggested natural selection

Darwin’s insight in 1838 - quickly developed this into theory explaining how all living things evolved into their diverse forms

and then... silence

"is the most powerful and the most comprehensive idea that has ever arisen on earth. It helps us understand our origins ... We are part of a total process, made of the same matter and operating by the same energy as the rest of the cosmos..." (Sir Julian Huxley)

Who mailed the paper to Darwin?

a) Robert FitzRoyb) Thomas Henry Huxleyc) Alfred Russell Wallace d) Sir Charles Lyelle) Samuel Wilberforce

Delayed publishing - started outline 1842

…until he received a paper in 1858 outlining natural selection

Friends arranged for joint reading of papers at Linnean Society - Darwin published ‘The Origin of Species’ in late 1859

Wallace’s paper stunned Darwin…

Darwin & Wallace disagreed on many issues regarding the details of HOW natural selection would work, butboth were convinced that it was the primary mechanismby which evolution occurred

Wallace: 1823-1913Darwin: 1809-1882

Basic outline of Darwin’s theory:

1. Individuals within a species differ in morphology, physiology, & behavior

2. Some of this variation is heritable

3. Organisms have a huge capacity for increase in numbers, but populations tend to remain +/- constant

4. As a result of competition, some variants will leave more offspring than others

5. If reproductive success is due to the varying trait, and that trait is heritable, it will be passed on to the offspring and become more common in the next generation

(Thus evolutionary change by natural selection)

‘Origin’ controversial among public - human descent from apes stressed

Among many scientists, concept of evolution was largely accepted

Much supporting evidence collected from paleontology, morphology, etc. to establish the fact of evolution

Mechanism of natural selection was not viewed as favorably - many doubted its power to produce evolution

Later, more serious objections e.g. about nature of heredity... do traits blend together in offspring?

Is it a problem for Darwin’s theory if inheritance works by blending (e.g. tall parent & short parent producekids of medium height)?

a) yes, it will remove the potential for variationb) no, it does not affect the potential for natural selection as

best adapted individuals still leave the most offspring

...and doubts about the age of the earth- Lord Kelvin estimated about 100 million years,

based on cooling of earth

Ooops. Didn’t know radioactivity continues to heat earth

What did Kelvin leave out of his calculations?

Darwin’s arguments for evolution & natural selection

Variation in domesticated forms: - great variation in animal breeds & cultivated plants

- deliberate selection to modify varieties

Variation in species in nature: - pointed to variation in individual traits (even in

‘important’ organs)- difficulty classifying: varieties vs. species

Eastern Screech-Owls

barnacles (Semibalanus)

Increase in numbers and competition:- calculated expected # of offspring if all survive- gave examples of increase for plants & animals

introduced to new areas

Ox-eye Daisies

Geological succession: - new species occur at intervals- ‘modern’ species may be found among extinct forms

- intermediate forms between orders found- older forms differ more from modern species

trilobite

- fossils belong to same groups as modern species in same area

Geographical distribution:- species isolated by strong barriers tend to be distinct,

though physical conditions are similar

Indigo Bunting Lazuli Bunting

- species in the same area are related, even if occupying different habitats

Eastern Gray Kangaroo

Lumholtz’sTree Kangaroo