We may get a clear idea of the way a man attains his social heritage by dropping figure for the present and speaking in the terms of plain natural science. Ever since Darwin propounded the law of Natural Selection the word Variation has been current in the sense explained on an earlier page.
The student in natural science has come to look for variations as the necessary preliminary to any new step of progress and adaptation in the sphere of organic life. Nature, we now know, is fruitful to an extraordinary degree. She produces many specimens of everything. It is a general fact of reproduction that the offspring of plant or animal is quite out of proportion in numbers to the parents that produce them, and often also to the means of living which await them. One plant produces seeds which are carried far and near--to the ocean and to the desert rocks, no less than to the soil in which they may take root and grow. Insects multiply at a rate which is simply inconceivable to our limited capacity for thinking in figures. Animals also produce more abundantly, and man has children in numbers which allow him to bury half his offspring yearly and yet increase the adult population from year to year. This means, of course, that whatever the inheritance is, all do not inherit it; some must go without a portion whenever the resources of nature, or the family, are in any degree limited and when competition is sharp.
Now Nature solves the problem among the animals in the simplest of ways. All the young born in the same family are not exactly alike; "variations" occur. There are those that are better nourished, those that have larger muscles, those that breathe deeper and run faster. So the question who of these shall inherit the earth, the fields, the air, the water--this is left to itself. The best of all the variations live, and the others die. Those that do live have thus, to all intents and purposes, been "selected" for the inheritance, just as really as if the parents of the species had left a will and had been able to enforce it. This is the principle of "Natural Selection."
Now, this way of looking at problems which involve aggregates of individuals and their distribution is becoming a habit of the age. Wherever the application of the principles of probability do not explain a statistical result--that is, wherever there seem to be influences which favour particular individuals at the expense of others--men turn at once to the occurrence of Variations for the justification of this seeming partiality of Nature. And what it means is that Nature is partial to individuals _in making them_, in their natural heredity, rather than after they are born.