sexually dimorphic, being in the original species larger in the cock than
in the hen. There is no convincing evidence that these appendages are
either for use or ornament. They are, in fact, a disadvantage to the bird,
being used by his adversary to take hold of when he strikes. The first
thing that happens when cocks fight is the bleeding and laceration of the
comb, as they peck at each other's heads. This laceration of the skin is,
in my view, the primary cause of the evolution of these structures,
leading to hypertrophy. But in this, as in other cases, the hereditary
result is regular, constant, and symmetrical, while the immediate effect
on the individual is doubtless irregular.



CHAPTER V

Mammalian Sexual Characters
Evidence Opposed To The Hormone Theory


Perhaps the most remarkable of all somatic sexual characters are those
which are almost universal in the whole class of Mammalia, the mammary
glands in the female, the scrotum in the male. We have considered the
evidence concerning the relation of the development and functional action
of the milk glands to hormones arising in the ovary or uterus, now we have
to consider the origin of the glands and of their peculiar physiology in
evolution. The obvious explanation from the Lamarckian point of view, and
in my opinion the true one, is that they owed their origin at the
beginning to the same stimulation which is applied to them now in every
female mammal that bears young. There is, as we have seen, a difficulty in
explaining how the occurrence of parturition causes the secretion of milk