160 THE OLDER HYBRIDISTS 
Following the modern usage, we shall apply the 
term ‘hybrid’ to all individuals arising from a cross 
between parents which belong to distinct groups, no 
matter whether these groups are separated as distinct 
genera or species, or whether they are regarded as 
representing only different races or varieties. This 
wide interpretation of the term hybrid has only re- 
cently been reintroduced. The use to which it has 
returned is, indeed, the original one ; but many inter- 
mediate writers, including Darwin, confined the em- 
ployment of this expression to cases of crossing between 
species, and applied the word ‘ mongrel’ to the off- 
spring of crosses between races or varieties of the same 
species. Darwin, however, did not regard species as 
differing in kind from varieties, and he even particu- 
larly emphasized the smallness of the distinction which 
can be drawn between the behaviour and properties 
of hybrids and mongrels respectively. Indeed, he 
came to the highly important conclusion that the laws 
of resemblance between parents and their children are 
the same, whatever may be the amount of difference 
between the parents in question—whether, that is to 
say, they are distinguished only by individual differ- 
ences, or whether they belong to separate varieties or 
even species. We have already seen that the more 
recent facts of biometry point strongly towards the 
conclusion that individual and race differences are 
inherited at approximately the same rate. It seems, 
however, to be at present somewhat doubtful whether 
all sorts of specific differences follow the same law of 
propagation on cross-breeding. 
