country, that the males come before the females. And the like holds
good with most of the migratory birds of the United States. (5. J.A.
Allen, on the Mammals and Winter Birds of Florida, Bulletin of
Comparative Zoology, Harvard College, p. 268.) The majority of the male
salmon in our rivers, on coming up from the sea, are ready to breed
before the females. So it appears to be with frogs and toads.
Throughout the great class of insects the males almost always are the
first to emerge from the pupal state, so that they generally abound for
a time before any females can be seen. (6. Even with those plants in
which the sexes are separate, the male flowers are generally mature
before the female. As first shewn by C.K. Sprengel, many hermaphrodite
plants are dichogamous; that is, their male and female organs are not
ready at the same time, so that they cannot be self-fertilised. Now in
such flowers, the pollen is in general matured before the stigma,
though there are exceptional cases in which the female organs are
beforehand.) The cause of this difference between the males and females
in their periods of arrival and maturity is sufficiently obvious. Those
males which annually first migrated into any country, or which in the
spring were first ready to breed, or were the most eager, would leave
the largest number of offspring; and these would tend to inherit
similar instincts and constitutions. It must be borne in mind that it
would have been impossible to change very materially the time of sexual
maturity in the females, without at the same time interfering with the
period of the production of the young a period which must be determined
by the seasons of the year. On the whole there can be no doubt that
with almost all animals, in which the sexes are separate, there is a
constantly recurrent struggle between the males for the possession of
the females.
Our difficulty in regard to sexual selection lies in understanding how
it is that the males which conquer other males, or those which prove
the most attractive to the females, leave a greater number of offspring
to inherit their superiority than their beaten and less attractive
rivals. Unless this result does follow, the characters which give to
certain males an advantage over others, could not be perfected and
augmented through sexual selection. When the sexes exist in exactly
equal numbers, the worst-endowed males will (except where polygamy
prevails), ultimately find females, and leave as many offspring, as
well fitted for their general habits of life, as the best-endowed
males. From various facts and considerations, I formerly inferred that
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