Chap. XXI. 
AND CONCLUDING KEMAEKS. 
399 
racters, when equally transmitted to both sexes can be 
distinguished from ordinary specific characters only by 
the light of analogy. The modifications acquired through 
sexual selection are often so strongly pronounced that 
the two sexes have frequently been ranked as distinct 
species, or even as distinct genera. Such strongly- 
marked differences must be in some manner highly im- 
portant ; and we know’ that they have been acquired in 
some instances at the cost not only of inconvenience, 
but of exposure to actual danger. 
The belief in the powder of sexual selection rest& 
chiefly on the following considerations. The characters 
which we have the best reason for supposing to have 
been thus acquired are confined to one sex ; and this 
alone renders it probable that they are in some way 
connected wdth the act of reproduction. These charac- 
ters in innumerable instances are fully developed only 
at maturity ; and often during only a part of the year,, 
which is always tlie breeding-season. The males (pass- 
ing over a few exceptional cases) are the most active in 
courtship ; they are the best armed, and are rendered 
the most attractive in various ways. It is to be espe- 
cially observed that the males display their attractions 
with elaborate care in the presence of the females ; 
and that they rarely or never display them excepting 
during the season of love. It is incredible that all this 
display should be purposeless. Lastly we have distinct 
evidence with some quadrupeds and birds that the indi- 
viduals of the one sex are capable of feeling a strong 
antipathy or preference for certain individuals of the 
opposite sex. 
Bearing these facts in mind, and not forgetting the 
marked results of man’s unconscious selection, it seems 
to me almost certain that if the individuals of one sex 
were during a long series of generations to prefer pair- 
