68
The Presidential Address.
venture to say that there are many extreme specialists, even
within the pale of science, who have but a vague idea of the
extremely important influence which this hypothesis has
upon their studies. On such an occasion as the present,
when, after recording our deep sense of gratitude to the man
who so nobly dedicated his life to the advancement of know-
ledge, it becomes my duty to direct your attention to his
works, I think that I cannot do better than occupy your
time by recapitulating the main points in the theory of the
origin of species.
Starting with the simple calculation showing the rate of
increase of any species as deduced from the number of young
produced at a birth, and comparing this with the actual
number of individuals at present existing, we find that an
immensely greater number of young must be produced than
ever survive. Thus, in the case of the elephant, which "is
reckoned the slowest breeder of all known animals," it is
seen that a single pair, supposing their offspring to survive
and to breed at the rate of six during a lifetime of a century,
would in the course of 740 to 750 years have given rise to
nearly nineteen million elephants living at the end of that
period.2 Similarly with birds, if we allow that one pair
produce four young ones per annum and breed but four
times during their life, in fifteen years this pair will have
increased to more than two thousand millions.3 Some in-
structive data have been quite recently given by Mr. P. L.
Simmonds4 with reference to the rabbit in Australia and
New Zealand, where this animal has become a perfect pest
within a period of twenty years since its first introduction.
"From New Zealand alone eight and a half millions of
rabbit-skins were exported in 1880, but this does not probably
represent one-tenth part of those actually destroyed. In that
climate the rabbit breeds nearly every month in the year.
But even supposing that a pair of rabbits do not breed
2 'Origin of Species,' 6th ed., p. 51.
3 A. R. Wallace's 'Contributions to the Theory of Natural Selection,'
p. 29.
4 Journ. Soe. Arts, Dec. 22nd, 1882, p. 99.