The Descent of Man

y the males alone of one family, and in another
family by the females alone, though in both
cases transmitted through the opposite as well
as through the same sex. (38. References are
given in my 'Variation of Animals and Plants
under Domestication,' vol. ii. p. 72.) Although
we are thus ignorant, the two following rules
seem often to hold good—that variations which
first appear in either sex at a late period of life,
tend to be developed in the same sex alone;
whilst variations which first appear early in life
in either sex tend to be developed in both sexes.
I am, however, far from supposing that this is
the sole determining cause. As I have not elsewhere
discussed this subject, and it has an
important bearing on sexual selection, I must
here enter into lengthy and somewhat intricate
details.
It is in itself probable that any character appearing
at an early age would tend to be inherited
equally by both sexes, for the sexes do not dif-