500 THE STRUCTURE OF EVOLUTIONARY THEORY
appears to me to be reasoning in a circle. Biology takes her time from
geology. The only reason we have for believing in the slow rate of the
change in living forms is the fact that they persist through a series of
deposits, which, geology informs us, have taken a long while to make. If
the geological clock is wrong, all the naturalist will have to do is to modify
his notions of the rapidity of change accordingly. And I venture to point out
that, when we are told that the limitation of the period during which living
beings inhabited this planet to one, two, or three hundred million years
requires a complete revolution in geological speculation, the onus probandi
rests on the maker of the assertion, who brings forward not a shadow of
evidence in its support (1869, year of publication of 1868 address, in
Huxley, 1894, pp. 328-329).And so Huxley, bowing to the physicists, concludes that geology has developed no
legitimate reason for discomfort with Kelvin's dates, while biology has similarly
failed to offer valid objection. Therefore, a little terminological misunderstanding,
and a minor battle over professional turf, can be resolved into the sweetness and
light of intellectual agreement. *
Huxley's acquiescence may not surprise us. After all, given his attraction to
saltationist ideas, Huxley had never shared Darwin's commitment to gradualism
and the attendant need for such ample geological time. But when we learn that A.
R. Wallace, a stouter defender of natural selection than Darwin himself, also
readily accepted Kelvin's dates, then we can better sense the idiosyncrasy of
Darwin's concern. Wallace ventured even further than Huxley. He published
several letters in Nature on the age of the earth and the measurement of geological
time (1870, 1892, 1893, 1895a and b). Wallace willingly accepted Kelvin's dates,
and he presented an ingenious argument to explain why some biologists had been
fooled into believing that evolution proceeded so slowly.
Working from a theory by James Croll linking ice ages to changes in the
earth's orbit, Wallace claimed that the last 60,000 years had experienced
extraordinary climatic stability due to unusually low orbital eccentricity. Before
then, and probably for most of geological time, orbital eccentricity had been more
pronounced, prompting climatic fluctuations in local areas, attendant deaths and
migrations of faunas, and a greatly accelerated rate of evolution. As an unfortunate
consequence of our generally valid uniformitarian method of measuring current
rates and extrapolating backwards, we developed the
- Huxley could never leave a conflict with such calm and no vitriol. Thus, as a
sample of his prose and personality, consider (from the same address) this incisive
passage on what a later generation would call GIGO. I would also read this statement as
an implied criticism of arrogance among physical scientists, an exercise in wound licking
after Kelvin's effective salvos: "Mathematics may be compared to a mill of exquisite
workmanship, which grinds you stuff of any degree of fineness; but, nevertheless, what
you get out depends upon what you put in it; and as the grandest mill in the world will
not extract wheatflour from peascods, so pages of formulae will not get a definite result
out of loose data" (1869, in 1894, p. 333).