Page:Popular Science Monthly Volume 48.djvu/530

488 the distinctions between genera are maintained. Consequently, the progress of evolution is not a smooth and uniform progression, but one that proceeds by jerks, through successive "sports" (as they are called), some of them implying considerable organic changes, and each in its turn being favored by natural selection.

Galton's explanation of this specific stability is as follows: The child inherits in part from the parents, in part from more remote ancestors; and since the sum of its ancestry, or, as Galton terms it, the mid-parentage, is on the average nearer than the exceptional parents to the mean of the race, the children of selected parents are on the average more mediocre than their parents.

I have tried to show that, while the child is descended from a long line of ancestors, it inherits from none but the two parents, and that it can only be said in a figurative sense to inherit from more remote ancestors. I shall soon refer to proofs that the persistency of inherited types is due to natural selection, and not to any principle of organic stability independent of selection.

If this is true, if the stability of specific types is due to the survival of the fittest, why do we have a type and not a fixed standard? If speed and strength and courage are good things, why is not every individual as swift as the swiftest, as brave as the bravest, and as strong as the strongest? Why does not every individual have every useful quality developed to the highest excellence to which it may attain in any individual of the species? Why should we find that diversity among individuals which usually passes under the name of "variation"?

We can measure strength and can treat it abstractly, and we can artificially select and breed from the strongest members of a stock, neglecting all other features; but this is not what takes place in Nature.

Here the most favored individuals are not the strongest, but the ones in which all the qualities of the species are most perfectly co-ordinated with each other in relation to the external world. Excessive strength may involve deficiency in some other essential, and the mean or average strength of the species is that degree of strength which is most in harmony with the mean degree of development of all the other characteristics of the species; and the individuals who depart too widely from this mean, either through excess of strength or deficient strength, are the ones which are exterminated.

Galton has himself given such a clear statement of the way a type is established by selection that it can not be improved upon, and I quote it in his own words:

"Suppose," he says, "that we are considering the stature of some animal that is liable to be hunted by certain beasts of prey in a particular country. So far as he is big of his kind, he would