440 Evolution and Adaptation 
and disadvantages (that are obvious as pointed out above), 
nor is it probable that in this way we can hope to get a final 
answer to our problem. We may begin by examining some 
of the modern hypotheses that have been advanced in this 
connection. 
Darwin has brought together a large number of facts 
which appear to show the beneficial effects of the union of 
germ-cells from two different individuals. Conversely, it is 
very generally believed, both by breeders and by some experi- 
menters, that self-fertilization in the case of hermaphroditic 
forms leads, in many cases, though apparently not in all, to 
the production of less vigorous offspring. Darwin’s general 
position is that it is an advantage to the offspring to have 
been derived from two parents rather than to have come 
from the union of the germ-cells of the same individual, and 
he sees, in the manifold contrivances in hermaphroditic ani- 
mals and plants to insure cross-fertilization, an adaptation for 
this purpose. 
This question of whether self-fertilization is less advan- 
tageous than cross-fertilization is, however, a different ques- 
tion from that of whether 2on-sexual methods of reproduction 
are less advantageous than sexual ones. Since some plants, 
like the banana, have been propagated for a very long time 
solely by non-sexual methods without any obvious detriment 
to them, it is at first sight not easy to see what other advan- 
tage could be gained by the sexual method. The case of the 
banana shows that some forms do not require a sexual 
method of propagation. Other forms, however, are so con- 
stituted, as we find them, that they cannot reproduce at the 
present time except by the sexual method. In other words, 
the latter are now adapted, as it were, to the sexual method, 
and there is no longer any choice between the two methods. 
The question of whether a non-sexual form might do better 
if it had another method of propagation is not, perhaps, a 
profitable question to discuss. 
