The Origin of Species
Divergence of Character
The principle, which I have designated by this term, is of high importance on my theory, and
explains, as I believe, several important facts. In the first place, varieties, even strongly-marked
ones, though having somewhat of the character of species as is shown by the hopeless doubts in
many cases how to rank them yet certainly differ from each other far less than do good and
distinct species. Nevertheless, according to my view, varieties are species in the process of
formation, or are, as I have called them, incipient species. How, then, does the lesser difference
between varieties become augmented into the greater difference between species? That this does
habitually happen, we must infer from most of the innumerable species throughout nature
presenting well-marked differences; whereas varieties, the supposed prototypes and parents of
future well-marked species, present slight and ill-defined differences. Mere chance, as we may
call it, might cause one variety to differ in some character from its parents, and the offspring of
this variety again to differ from its parent in the very same character and in a greater degree; but
this alone would never account for so habitual and large an amount of difference as that between
varieties of the same species and species of the same genus.
As has always been my practice, let us seek light on this head from our domestic productions.
We shall here find something analogous. A fancier is struck by a pigeon having a slightly shorter
beak; another fancier is struck by a pigeon having a rather longer beak; and on the acknowledged
principle that 'fanciers do not and will not admire a medium standard, but like extremes,' they
both go on (as has actually occurred with tumbler-pigeons) choosing and breeding from birds
with longer and longer beaks, or with shorter and shorter beaks. Again, we may suppose that at
an early period one man preferred swifter horses; another stronger and more bulky horses. The
early differences would be very slight; in the course of time, from the continued selection of
swifter horses by some breeders, and of stronger ones by others, the differences would become
greater, and would be noted as forming two sub-breeds; finally, after the lapse of centuries, the
sub-breeds would become converted into two well-established and distinct breeds. As the
differences slowly become greater, the inferior animals with intermediate characters, being
neither very swift nor very strong, will have been neglected, and will have tended to disappear.
Here, then, we see in man's productions the action of what may be called the principle of
divergence, causing differences, at first barely appreciable, steadily to increase, and the breeds to
diverge in character both from each other and from their common parent.
But how, it may be asked, can any analogous principle apply in nature? I believe it can and does