former state the more
common)]. In the course of a thousand generations infinitesimally small
differences must inevitably tell{59}; when unusually cold winter, or hot
or dry summer comes, then out of the whole body of individuals of any
species, if there be the smallest differences in their structure,
habits, instincts [senses], health &c, <it> will on an average tell; as
conditions change a rather larger proportion will be preserved: so if
the chief check to increase falls on seeds or eggs, so will, in the
course of 1000 generations or ten thousand, those seeds (like one with
down to fly{60}) which fly furthest and get scattered most ultimately
rear most plants, and such small differences tend to be hereditary like
shades of expression in human countenance. So if one parent <?> fish
deposits its egg in infinitesimally different circumstances, as in
rather shallower or deeper water &c., it will then <?> tell.

{59} In a rough summary at the close of the Essay, occur the
words:--"Every creature lives by a struggle, smallest grain in
balance must tell."

{60} Cf. _Origin_, Ed. i. p. 77, vi. p. 94.

Let hares{61} increase very slowly from change of climate affecting
peculiar plants, and some other <illegible> rabbit decrease in same
proportion [let this unsettle organisation of], a canine animal, who
formerly derived its chief sustenance by springing on rabbits or
running them by scent, must decrease too and might thus readily become
exterminated. But if its form varied very slightly, the long legged
fleet ones, during a thousand years being selected, and the less fleet
rigidly destroyed must, if no law of nature be opposed to it, alter
forms.

{61} This is a repetition of what is given at p. 6.

Remember how soon Bakewell on the same principle altered cattle and
Western, sheep,--carefully avoiding a cross (pigeons) with any breed.
We cannot suppose that one plant tends to vary in fruit and another
in flower, and another in flower and foliage,--some have been selected
for both fruit and flower: that one animal varies in its covering and
another not,--another in its milk. Take any organism and ask what is
it useful for and on that point it will be found to vary,--cabbages
in their leaf,--corn in size <and> quality of grain, both in times
of year,--kidney beans for young pod and cotton for envelope of seeds
&c. &c.: dogs in intellect, courage, fleetness and smell <?>: pigeons
in peculiarities