128 Ww. R. B. ROBERTSON 
all possible combinations of similar variations in the twenty- 
seven other pairs. Such might be the basis of all of our variations 
in guinea-pig inheritance. 
It is noticeable in any animal or plant which becomes domesti- 
cated that very soon there appear whites, blacks, browns, spotted, 
yellows and others of the color varieties common to domesticated 
species. The same may be said of other characters of the species, 
size for instance. On domestication inbreeding occurs. This 
gives rise to homozygous strains, which may be isolated. In the 
wild state inbreeding is not so prevalent. Promiscuous mixing 
occurs. A summing up of the characters results and all normals, 
which are usually dominant, are present and show. The weaker 
recessive characters, if present, are covered up. They exist 
in the single or heterozygous condition and so do not show. If 
they exist in the homozygous condition they may show, as in 
albinos, but the organisms may be killed off by natural selection. 
Under domestication man preserves these recessives. 
The loss of parts of chromosomes may explain very easily the 
appearance of such phenomena in the domestication of species. 
The fact that there appear always the same or nearly the same 
color varieties in each species may be due to this, that their 
chromosomes are more or less similarly organized, that there 
are approximately the same number and in many respects the 
same individual chromosomes to be dealt with in each species, 
and finally, that these chromosome pairs are subject to the same 
vicissitudes of fortune in division at the maturation period in 
each species. True, there are minor variations. in chromosomes 
as we pass from species to species. There are also minor vari- 
ations in color inheritance as we pass from species to species. 
But these variations are small when we think of the similarities. 
All species of rodents show grays, all show albinos, all show 
blacks, all show some form of brown, and yellows. The method 
of inheritance of the yellows, for instance, might vary from species 
to species, but they are yellow, nevertheless. 
The same spontaneous variations, such as albinism, probably 
occur not once but over and over again in the same species in 
various parts of the world entirely independently of each other. 
