Page:Popular Science Monthly Volume 68.djvu/498

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It will be noticed that the differences between the normally fed individuals and those subjected to famine are not species-making differences, as specific characters go with the Lepidoptera, there being no differences in color or patterns, or shape or venation of wings, or larval or adult ornamentation. If a species or race of silkworms were named on the basis of characters induced by famine, it would be a 'size' and 'season' species—a Lilliputian race of silkworms having a lengthy metamorphosis.

While at first glance these experiments might seem to offer an instance of the inheritance of acquired characters, it is, however, apparent that the underfeeding affects the nourishment and full development, not only of visible parts of the body, but also of the germ cells and all internal parts of the body. The germ cells need not be said, therefore, to have been influenced by the acquired somatic characters and to have transmitted them as such, but rather they may be said through their own lessened vitality to have produced progeny with characteristics so parallel to those of the parent soma as to make it appear an authentic case of the inheritance of acquired characters. We have, therefore, a case of transmission of imperfect nutrition, not one of true heredity, a distinction made clear by Weismann. Moreover, if acquired characters are really hereditary, their inheritance should last for more than three generations.

One interesting result of this experiment is that (in so far as silkworm testimony goes) temporary trying conditions do not handicap the race in the long run. It is even conceivable that the ultimate result of famine might be a strengthening of the race (physically speaking), the famine playing the part of a selective agent, preserving only the strong and adaptable.

Of like nature, but often far greater in degree, are the changes in the individual dependent on differences in food, in nurture or in surroundings generally. In the life of a plant the environmental variations may be so great as apparently to overshadow all the innate characters or peculiarities. With the higher animals the direct effect of environment is proportionately less, and it reaches its minimum among birds and the more specialized insects. Yet no individual of any species is without some traits of variation due entirely to environmental influences. In fact heredity does not repeat the traits of the parent, but merely the tendency to develop similar traits under similar conditions. Change utterly the conditions of growth, and the same heredity will show itself in very different results. Strictly speaking,