What is this Natural Selection which has been dead for half a century,
but which Mr. Belloc still exerts himself industriously through four
long papers to kill all over again? It is the purest common-sense, the
most obvious deduction from obvious facts. I have set out the idea as
plainly as I could in the _Outline of History_ Mr. Belloc is attacking.
It is put so plainly there that, before he can begin to argue against
it, he has to misstate it; he has to tell the story all over again
in his own words and get it suitably askew. It was quite open to
him to quote from my account, but he preferred to compile his own
misstatement. Indeed, in all this argument against Natural Selection
he never once quotes my actual words. He paraphrases throughout.
He has put some words between inverted commas in one place, so as
inadvertently to produce the impression that they are mine, but they
are not mine.
Now the facts upon which the idea of Natural Selection rests are
matters of universal knowledge. “Every species of living thing is
continually dying and being born again as a multitude of fresh
individuals”; that is the primary fact. No species seems to be
perfectly adapted to its conditions, and even the happiest species
tends to multiply until it is in a state of need and pressure. So
far surely we are dealing with things beyond dispute. And next comes
the fact of individuality. Every living unit is individual with
a difference of its own. Every individual has its own distinctive
differences, and each of these differences may or may not be an
advantage or a disadvantage. Individuals with advantageous differences
will generally get on better in life, prosper and so be able to breed
more freely, than those with disadvantageous differences. Offspring
have a tendency to repeat the distinctive differences of their parents.
Therefore, taking a species as a whole by the million or billion or
million billion--for few species of animals or plants are represented
by fewer individuals than a million--there will be in each successive
generation a greater number of individuals with the differences that
are advantageous relative to the number with disadvantages. In other
words, the average of the species will have moved more or less in the
direction of the advantageous differences, whatever they may be, and
however numerous they may be. If, for example, the species is chased
and has to climb or run for it, there will be rather more good climbers
and sprinters in the new generation. There may be other dangers and
other needs; they will not affect the premium set on quickness and the
fate of the slow. And if the circumstances of the species continue to
press in the same direction, the movement of the average will be in
the same direction in this respect for so long as they continue to
press. Over a few score or even a few hundred generations, and under
conditions not very strenuous, a species may not change very much.
It may seem to be _fixed_ in its general characteristics, just as the
continents seem to be fixed in their general outline. But, as the range
of time extends and the pressure of necessity continues, the change
becomes more striking.