SUMMARY. 
235 
c «. 
«>. XVI. 
' llT 'ing a lengthened period have produced some definite 
^fi^ct on both sexes, the more important result will have 
’ a< -' n an increased tendency to fluctuating variability or 
0 a,I gmented individual differences; and such differ- 
^ Ce s will have afforded an excellent groundwork for 
J, ;‘ action of sexual selection. 
J’he laws of inheritance, irrespectively of selection, 
a Ppear to have determined whether the characters ac- 
j'lired by the males for the sake of ornament, for pro- 
1 Ucitl g various sounds, and for fighting together, have 
e, - J1 transmitted to the males alone or to botii sexes, 
e, ther permanently or periodically during certain sea- 
s ° lis of the year. Why various characters should sonie- 
have been transmitted in one way and sometimes 
Mother is, in most cases, not known ; but the period 
Variability seems often to have been the determining 
r ' ai| se. When the two sexes have inherited all charac- 
| f ‘ ls in common they necessarily resemble each other ; 
^ as the successive variations may be differently trans- 
mitted, every possible gradation may he found, even 
'''thin the same genus, from the closest similarity to 
l ° widest dissimilarity between the sexes. With many 
' ' ,S( dy-ailied species, following nearly the same habits 
°J life, the males have come to differ from each other 
hlefly through the action of sexual selection; whilst 
. It! females have come to differ chiefly from partaking 
m a greater or lesser degree of the characters thus 
8ft 
vfiuired by the males. The effects, moreover, of the 
, finite action of the conditions of life, will not have 
l^ eu masked in the females, as in the case of the males, 
the accumulation through sexual selection of strongly- 
< 1,J nouuced colours and other ornaments. The iudi- 
j_ 1( luals of both sexes, however affected, will have been 
^'Tt at each successive period nearly uniform by the 
ee intercrossing of many individuals. 
