68 
POPULAR SCIENCE REVIEW. 
as mere varieties. But if it be thought that at least all the connecting link 8 
between any series of forms ought to be present, if not in the fossil at least 
in the living state, it should be remembered that the very process of natural 
selection prevents this, each succeeding variety crushing out that which 
preceded it, because in this struggle for life it has the greater number of 
advantages. Two elements, however^ in the argument are well sustained in: 
the following passages. The first relates to the certainty of the struggle for 
existence : — 
(l There is no exception to the rule that every organic being naturally 
increases at so high a rate, that if not destroyed, the earth would soon be 
covered by the progeny of a single pair. Even slow-breeding man has 
doubled in twenty-five years. At this rate, in a few thousand years there 
would literally not be standing-room for his progeny. Linnaeus has calcu- 
lated that if an annual plant produced only two seeds, and there is no plant 
nearly so unproductive as this, and these seedlings next year produced two, 
and so on, then in twenty years there would be a million. The elephant is 
reckoned the slowest breeder of all known animals, and I have taken some 
pains to estimate its probable minimum rate of natural increase : it will be 
under the mark to assume that it begins breeding when thirty years old, 
and goes on breeding till ninety years old, bringing forth three pair of young 
in this interval ; if this be so, at the end of the fifth century there would 
be alive fifteen million elephants, descended from the first pair.” 
The second passage which we quote from Mr. Darwin, shows in a popular 
manner, which must appeal to the reason of every ordinarily intelligent 
person, what an enormous length of time is required in order to produce even 
a moderate degree of variation, and bears forcibly upon the question which 
the opponents of Natural Selection so often put , u Why do we not find inter- 
mediate forms ? ” 
a No one would expect to raise a first-rate melting pear from the seed of 
the wild pear, though he might succeed from a poor seedling growing wild, 
if it had come from a garden stock. The pear, though cultivated in classical 
times, appears, from Pliny’s description, to have been a fruit of very inferior 
quality. I have seen great surprise expressed in horticultural works at the 
wonderful skill of gardeners in having produced such splendid results from 
such poor materials ; but the art has been simple, and, as far as the final 
result is concerned, has been followed almost unconsciously. It has con- 
sisted in always cultivating the best known variety, saving its seeds, and 
when a slightly better variety has chanced to appear selecting it, and so on- 
wards. But the gardeners of the classical period, who cultivated the best 
pear they could procure, never thought what splendid fruit we should eat ; 
though we owe our excellent fruit in some small degree to their having 
naturally chosen and preserved the best varieties they could anywhere find. 
u A large amount of change in our cultivated plants, thus slowly and un- 
consciously accumulated, explains, as I believe, the well-known fact, that 
in a vast number of cases we cannot recognise, and therefore do not know, 
the wild parent stocks of the plants which have been longest cultivated in 
our flower and kitchen gardens.” 
The phenomena which have been grouped together under the term Instinct 
have been a powerful weapon in the hands of those who combat the Dar- 
winian doctrine. It is interesting, therefore, to observe how the author deals 
with this part of the subject. In trying to account for the instincts of 
animals, Mr. Darwin takes two courses: first he endeavours to show how, by 
the law of natural selection, what is called instinct is little more than habit. 
