Page:Popular Science Monthly Volume 82.djvu/397

Rh direct effects of the environment, and are not inherited. To-day, we must throw these out and consider heritable variations only. Now we find that these heritable variations mainly (at least) represent no more than a shuffling of the stock-in-trade of the organism, and if any of them involve absolutely new determiners, we do not know it. The matter is complicated by the frequent appearance of new characters, which experimental evidence shows to result from new combinations of the old ones. Thus the pink-flowered and yellow-flowered stocks (Matthiola) give white and red-cream flowers in the third (second filial) generation, no matter if the two original strains had been bred true and had remained constant from the beginning of time. Here we seem to see something entirely new, but analysis shows that we have no more than new combinations of certain of the grandparental characters.

What will natural selection do with such materials? It can do no more than favor certain characters or combinations of characters and eliminate others. It can not even eliminate the recessives. The result will be the production of a number of distinct types, without necessarily any forward evolution—anything more than a shuffling and sorting of determiners. So far as we can see, this is exactly what has happened in the case of the oak leaves and many mollusc shells.

The modern school of Mendelian experimenters, who have from necessity confined themselves to determining the inheritance of relatively simple characters, have come to think little of natural selection. They have seen how various combinations can arise, greatly altering the appearance of animals and plants, without selection having anything to do in the matter. They have also seen how certain of these modified types, or others like them, may multiply and spread, without being obviously helped or hindered by selective agencies. Where the characters came from, they do not know; but neither do the selectionists. Let it suffice that we have here an apparently mechanical arrangement, which if left to itself will people the earth with diverse animals and plants, a large proportion of which will get along well enough to survive. Possibly this description is unjust in its application to modern experimenters generally, but it at least represents the attitude of some of the more influential and at the same time marks the recognition of a number of real and important facts. I think that while we shall gladly incorporate the facts into our system, we shall in time come to wonder at the limited view of nature implied by the attitude described. It is all too simple and too easy, it does not take into account the real complexities of life or of organization. It reminds us a little of the school of zoogeographers who would bridge the oceans whenever it seems necessary for some animal to cross, or to have crossed. The experimental work itself is revealing this, as day by day new complications arise.