caused the growth and development of man's spiritual, mental, and moral nature. Human nature is to-day essentially the same as it was thousands of years ago. The great achievements of modern man are intellectual and dependent upon accumulated stores of information and knowledge. They are not moral attainments. The thin veneer of civilization is the charitable cloak which covers much brutality, deceit, and egotism, and no little hypocrisy, which often serves pleasantly to beguile the dead monotony of dissimulation. SOCIAL EVOLUTION I VARIATION AND HEREDITY 1 It is a fact of general observation that the offspring of plants and animals tend to resemble the particular individuals from which they have sprung. "The young of a horse is always a horse and never a zebra. Wolves do not give birth to foxes. Sunflowers will not grow from thistle seed." Nature keeps things in order, or, as the biologist says, plants and animals breed true. We have come to regard this relation as an established principle. But in Ancient and Medieval times many people believed that certain plants transformed into animals. In the Middle Ages they thought that the barnacle-goose originated from the goose-barnacle. 1a Since then, our knowledge of natural law has so greatly increased that we are able to assert with utmost confidence that plants and animals breed true. This likeness of parent and offspring is of such a nature that the young usually bear a somewhat close resemblance to their parents, in addition to sharing the wider similarity of structure and function which makes them belong to the same species as their parents. Thus the resemblance is both detailed and general. The offspring of domestic cattle are like their parents in such characteristics as size, form, color, and amount of milk.1b 1 Metcalf, M. M.-Organic Evolution, 3rd ed., 1911, p. 3. 1-a Ibid. 1-b Ibid., p. 6. 3 The resemblance of parent and offspring is, however, not exact enough to be duplication. The family likeness is such that parents and progeny are quite distinguishable. "Tom" has his own individuality, and "Molly" has her peculiarities. Thus we see that there are individual differences which indicate how much the offspring vary from their parents and among themselves. The facts of individual difference we call variation. Our knowledge of variation permits us to say "that while, under the influence of heredity, the young tend to resemble their parents, because of variation this resemblance is more or less imperfect.2 To be convinced of this fact of variation one has only to take a few hundred individuals of any species and compare them with reference to any single trait. If one measure the lengths of a thousand oak leaves taken from the same tree, he will find that some are considerably longer than others, but that within certain limits most of the leaves have approximately the same length. So it is with any trait of any plant or animal,—there is much variation. The winter birds of east Florida show a variation in size of from fifteen to twenty per cent. among specimens of the same species and sex when taken in the same locality. Thus the relation between parents and offspring is of such a nature that like tends to beget like, yet at the same time opportunity is allowed for the individual differences which we have called variations. But how does it happen that like tends to beget like? Why is it that the young of a horse will always be a horse and not a zebra? How is it that nature keeps things in order? For some time biologists have known that "when the parent's body is developing from the fertilized ovum, a resi2 Ibid., p. 7. |