VII 
ON THE INFERTILITY OF CROSSES 
161 
breeding by securing several hybrids from quite distinct 
stocks to start with, ’and by having two or more sets of experi¬ 
ments carried on at once, so that crosses between the hybrids 
produced may be occasionally made. Till this is done no 
experiments, such as those hitherto tried, can be held to prove 
that hybrids are in all cases infertile inter se. 
It has, however, been denied by Mr. A. H. Huth, in his 
interesting work on The Marriage of Near Kin, that any 
amount of breeding in-and-in is in itself hurtful; and he quotes 
the evidence of numerous breeders whose choicest stocks have 
always been so bred, as well as cases like the Porto Santo 
rabbits, the goats of Juan Fernandez, and other cases in which 
animals allowed to run wild have increased prodigiously and 
continued in perfect health and vigour, although all derived 
from a single pair. But in all these cases there has been 
rigid selection by which the weak or the infertile have been 
eliminated, and with such selection there is no doubt that the 
ill effects of close interbreeding can be prevented for a long 
time ; but this by no means proves that no ill effects are pro¬ 
duced. Mr. Huth himself quotes M. Allie, M. Aube, Stephens, 
Giblett, Sir John Sebright, Youatt, Druce, Lord Weston, and 
other eminent breeders, as finding from experience that close 
interbreeding does produce bad effects; and it cannot be 
supposed that there would be such a consensus of opinion 
on this point if the evil were altogether imaginary. Mr. 
Huth argues, that the evil results which do occur do not 
depend on the close interbreeding itself, but on the tendency 
it has to perpetuate any constitutional weakness or other 
hereditary taints ; and he attempts to prove this by the argu¬ 
ment that “ if crosses act by virtue of being a cross, and not 
by virtue of removing an hereditary taint, then the greater the 
difference between the two animals crossed the more beneficial 
will that act be.” He then shows that, the wider the difference 
the less is the benefit, and concludes that a cross, as such, has 
no beneficial effect. A parallel argument would be, that change 
of air, as from inland to the sea-coast, or from a low to an 
elevated site, is not beneficial in itself, because, if so, a change 
to the tropics or to the polar regions should be more beneficial. 
In both these cases it may well be that no benefit would 
accrue to a person in perfect health ; but then there is no 
