Kevin T. Kelly
Department of Philosophy
Carnegie Mellon University
Stalemate:
Huxley: speciation through selection was hypothetical and recommended saltations as well.
Fleeming Jenkin (1833-35): Scottish engineer, associate of William Thomson (Lord Kelvin). Artificial selection disproves evolution by natural selection: species boundary never crossed. Instead, asymptotic reduction in variability up to a limit.
Darwin: Always possible to change a bit further. Changing environmental circumstances may increase variability.
Struggle for existence conceded by all.
Some denied evolution altogether: at the scientific margin.
Most biologists accepted natural selection and evolution, but didn't think natural selection was sufficient.
Darwin: Large, undirected changes are monstrosities, which will be sterile and nonadaptive. That is why small variations guided by selection are required.
New evidence:
Henry Walter Bates (Wallace's travelling companion):
Wallace: sexual dimorphism results from natural selection of dull females, not sexual selection of colorful males. Darwin digs in.
Moritz Wagner, German naturalist: importance of isolation in natural selection to prevent dilution of new variety.
Darwin:
St. George Jackson Mivart (1827-1900) friend of Huxley: Eye objection: natural selection couldn't produce something as complex as the eye.
Particulate vs. blending. Hair color is blending, sexuality non-blending (whole penis or none).
Darwin favors blending.
Problem:
Fleeming Jenkin: (Victorian example!) White castaway superior to black natives, but his advantage would be swamped in one generation, prior to selection against black competitors.
Darwin: White castaway is like a large variation. Jenkin proved Darwin was right that large saltations cannot drive evolution!
Counter-response: small individual differences are too small to be selected for.
Darwin's pangenesis theory: Gemmules given off from each part of the body to the germ cells. This explains:
Mivart: If Pangenesis were true, Jews would would inherit circumcision, since the gemmules would never get transmitted!
Francis Galton (Darwin's cousin): transfusions don't affect heredity in rabbits. So blood can't carry gemmules from all parts of the body to the sex organs!
Darwin starts to doubt the Origin view that sterility between species is not selected for.
Darwin's explanation
Counterevidence: Lythrum salicaria violates predicted negative correlation between probability of fertilization and fertility rate.
Wallace disagreed: Darwin admitted lack of interest in breeding can be selected for and this amounts to infertility.
John Philips, prof. of geology at Oxford, President Geological Society of Britain:
Good news:
Time for natural selection:
Almost good news: foraminer "eozoon canadense" (dawn animal of canada). J. William Dawson, principal of McGill, W. B. Carpenter, leading authority on foraminifers.
Philips: Ganges did more work than denudation of the weald in 1.3 million years. Darwin's crude estimate of 3000 million years is too long. Cambrian at most 95 million years ago.
Denudation of weald struck from 3rd edition. Darwin: "...I so consumedly burned my fingers with the Wealden".
Kelvin and Jenkin: Thermodynamics: If Earth's interior heat is from primal formation from a nebula, then due to the exponential pace of cooling (basically same differential equation as population growth), the Earth is around 98 million years old. Darwin's son George was Kelvin's assistant!
Huxley's response: if the geological record runs faster, then evolution must also run faster to suit. Kelvin unimpressed: the point is to explain how leisurely natural selection from individual differences could work that fast.
Wallace's response: Glaciation is tied to the eccentricity of the Earth's orbit. Periods of high eccentricity are stressful and drive faster changes than we see now, in a period of low glaciation.
Darwin: a little of Wallace, a little Lamarckianism, and digging in to wait for a change in physics.
Starting point for Wallace and Darwin.
Even Lyell converted to Darwinism based on geographical distribution in 1865-8.
Special creation predicts maximally adapted beings for the places they are.
In fact, continental forms facing bigger competitions frequently wipe out isolated island forms. So God made a mistake with the native form.
Alfred Newton, prof. of zoology at Cambridge: Distribution proves evolution, not natural selection. Open question.
Hooker: Greenland flora has higher percentage of Scandinavian forms compared to North American forms. North America has greater number of Scandinavian forms. Explanation: Ice age drove Scandinavian forms Southward. In North America, they formed new species in warmer climes. In Greenland, warmest species were exterminated.
Wallace: widely distributed butterflies vary more than narrowly distributed, illustrating force of natural selection.
Again, homology argues for common ancestry, not the sufficiency of natural selection.
Owen outwardly approved of Darwinism, secretly wrote negative review. Said Vestiges was better, and Owen's view better still.
A few years later, Owen endorsed evolution and claimed he said it earlier.
1859-1875: Most biologists convertto evolutionism.
Most still skeptical about natural selection as a primary mechanism. Darwin's tinkering with later editions doesn't help the case.
Ruse's theory: accepting evolution made people feel "progressive enough" not to go farther.
Better theory: the strongest evidence for evolution did not single out natural selection as an evolutionary mechanism. Without a genetic theory, acquisition of acquired characteristics was equally plausible. But natural selection helped to support evolution by showing one way in which it would happen.
Hooker, Bates, Wallace all used natural selection in biological problem solving, focused on geographical distribution (the Darwinian paradigm). This group found natural selection sufficient.
Opponents were not a united front and were not actively involved in problem solving e.g., Spencer.
Resolution of genetics:
Mendel's non-mixing genetics (1860) ignored until 1900 when rediscovered.
1900 August Weismann: argued that sex cells exist independently of the rest of the body,undermining Lamarckism.
T.H. M organ (New York) "classical theory of the gene".
Until 1930's, Mendelian genetics was thought to support saltationism. After 1930s, the view was that the variations would be small.
Resolution of age of Earth: Discovery of radioactivity.
Continuing debate over natural selection: drift, sexual selection, group selection.