575. 233 
The Species, the Sex, and the Individual 
Past, LI. 
HAVE been discussing characters that are related to sexual court- 
ship, but among characters confined to one sex there are others 
which are connected with other actions. For instance, there are struc- 
tural peculiarities which are only employed in combat. Among the 
most highly developed of -these are the antlers of stags. It cannot 
be disputed that these are the special, apparently the only weapons 
of the stag, and that there is no stag in a state of nature which does 
not regularly follow the practice of duelling without any variation 
in the arms employed. But those who consider that the evolution 
of the antlers is sufficiently explained by the constant victory and 
survival of the stags which have them most developed, leave out of 
view important problems :—-Firstly, why do the antlers only begin 
to develop when the stag becomes mature; Secondly, why are they 
renewed every summer, and drop off again in spring? In relation 
to these problems it is at least significant that the males only fight 
when they begin to breed, and, when mature, only in the breeding 
season, which is limited to the autumnal months. As the fighting 
of stags is fierce and frequent, it is quite possible that the irritation 
due to butting with the forehead was the exciting cause in the 
beginning, and has been ever since, of the remarkable outgrowth of 
bony tissue which forms the antlers. If this were so, it would be 
physiologically intelligible that when the stimulation ceases at the 
end of the butting season and the circulation becomes less active, 
the bone should cease to grow, should become dry and brittle, and 
then the antlers should either drop off of their own accord, or 
be intentionally broken off by the stag. Next season a renewal of 
the fighting would cause a renewal of the growth. My theory is, 
that stimulations periodically repeated, physiologically cause periodi- 
cal phenomena of growth, and that these rhythmical processes of 
growth repeated in successive generations ultimately become heredi- 
tary. It is, or has been, a current belief that effects so caused are 
not inherited; but such inheritance has not yet. been proved to be 
impossible. I am only attempting to show that the facts seem to 
lead inductively to the conclusion that. structural evolution has 
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