PROGRESSIVE HEREDITY. 171 
reversion to the three-toed’ historical ancestors of the 
present genus. These vouchers are sufficient. 
All the phenomena of artificial breeding, as well as 
natural’ selection, serve to show that not only the cha- 
racters descended from past ages, but also those subse- 
quently and most recently acquired, may be transmitted 
to posterity. This is progressive heredity. Without 
it, improvement and progress would be impossible ; and 
its own possibility is the direct result of the nature of 
reproduction. The newer a useful modification, the less 
has it hitherto been able to place itself in correlation 
with the entire organism, the less is the reproductive 
system as yet affected by it; the more uncertain and 
fluctuating, therefore, is the transfer by propagation ; 
breeding, or natural selection, is requisite to convert the 
potentiality of progress into a fact, and gradually to 
enrol this fact among the conservative inheritances, 
Progressive heredity is naturally more complex where 
the sexes are separate, where sexual selection asserts 
its rights, and the advantages of one sex are fostered 
by the taste of the other, and are then either trans- 
ferred exclusively to the sex benefited by its secondary 
characters, or turned to the profit of the whole species. 
Asa rule, the males are endowed with these advantages, 
and have transmitted them incompletely to the females. 
We will explain ‘ourselves by a single example. In the 
order of insects termed Orthoptera (or straight-winged), 
the males, by rubbing their wing-covers together, or by 
stroking them with the lower portion of their hind legs, 
are able to make a music attractive to the females, 
Von Graber, a distinguished modern entomologist, has 
shown” that the teeth of the stridulating instruments of 
