43 
are at the present time constant and inherent. He has 
begun with a single race, and out of that single race he 
has produced many, differing alike from their common pro- 
genitor, and from each other. These new races breed true, 
i. e.j steadily transmit their peculiarities by reproduction; 
they are independent of local and temporary circumstances ; 
in fact, they are neither more nor less than species, and 
would unhesitatingly be recognized as such by naturalists if 
then* origin were only unknown. It is unnecessary to instance 
particular examples, the facts are patent to every one, whether 
in respect to cattle, horses, dogs, fowls, vegetables, or flowers. 
How then has man done this ? He has done it simply by avail- 
ing himself of observed natural variations, which he has trusted 
to inheritance to perpetuate. Directly to produce variation 
is entirely beyond his power, he knows nothing of its causes, 
and can in no way influence it. He simply selects, and so 
controls. The variations in character in individuals of any 
species do not as a general rule tend to effect any specific 
change, if intercrossing be freely permitted, because they are 
perpetually neutralizing one another. But man, perceiving 
some variation useful to himself, isolates and preserves it by 
preventing the intercrossing which is calculated to destroy 
it. The process is repeated generation after generation, with 
the like precaution, until at last the variation is fixed, it has 
become specific. Wliile, therefore, these facts concerning 
breeds prove conclusively that variation and inheritance can 
produce species, they show, further, that to do this a certain 
selection is necessary to prevent the counteracting influence 
of intercrosses. In the case of domestic breeds this is done by 
man's arbitrary isolation. Is there anything in Nature corre- 
sponding to this, and capable of producing the like effect ? 
Undoubtedly there is. In some cases there is the very same 
thing at work, — isolation ; a few individuals of a species are 
often separated locally from all others, and exposed, therefore, 
to but little intercrossing. If variations occurred here, there 
would manifestly be far greater chance,- so far, of their being 
perpetuated and becoming specific, than in a locality where a 
large number were to be found together. More important, 
however, than this, as more generally applicable, and really 
more potent, is the principle which Mr. Darwin has deno- 
minated Natural Selection, and which forms the key to 
his whole hypothesis. All living beings reproduce themselves 
in a geometrical ratio of increase, which must inevitably lead 
to an overcrowding, a jostling, a struggle, both for position 
and subsistence. The fact that it is so is indisputable. What 
follows, then ? Clearly there must be a selection perpetually 
