Page:Popular Science Monthly Volume 48.djvu/528

486 shot in its career. In rare cases a long run of luck continues to favor the course of a particular shot toward either outside place, but in the large majority of instances the number of accidents that cause deviation to the right balance in a greater or less degree those that cause deviation to the left. Therefore most of the shot finds its way into the compartments that are situated near to a perpendicular line drawn from the outlet of the funnel, and the frequency with which shots stray to different distances to the right and left of that line diminishes in a much faster ratio than these distances increase.

Types which are based upon vital statistics have peculiar interest, since they persist from generation to generation, according to what is known as the law of specific stability, while they also undergo slow changes according to the principle of the mutability of species.

Individuals come and go, but the type persists, and its slow changes may be pictured as quite independent of and more substantial than the procession of individuals which files past only to vanish from the world.

The statistical comparison of vital types affords a means for studying the phenomena of inheritance by the exact methods of mathematics, and it is capable of yielding definite and valuable results, so far as the vital phenomena which are studied can be treated as if they stood alone, but the attempt to generalize from vital statistics and to deduce general laws of inheritance from them is attended by peculiar difficulties, due in great part to the fact that the data which are studied are not separable from the organism which exhibits them. Stature or size or weight may be treated abstractly for statistical purposes, but the stature of an organism is not an abstraction, for the organism is not only a bundle of properties, but a unit as well, and its stature is only one among many features which are all beautifully co-ordinated with each other in such a way as to promote the welfare of the species. A generalization which ignores this fact and treats stature as an abstraction may, while proved by statistics, be untrustworthy as a contribution to our knowledge of inheritance.

In popular language, specific stability may be said to be due to inheritance, and specific mutability to variation; but in this connection these words have only a loose meaning. In so far as they convey the impression that the stability of species and the mutability of species are antagonistic to each other, or are due to two distinct and opposing influences, these terms are unfortunate, for we have good ground for holding that they are due to the same influence—the extermination of certain individual peculiarities, and the preservation of others by natural selection.

The older naturalists held that adherence to type is due to