Some animals remain with the eggs for a time as if to guard them. Such a habit is found in the female of the newt Desmognathus; and the python coils about its eggs, whose hatching is said to be facilitated by the warmth received from the parent's body. In almost all of the birds the eggs are objects of great

downy young chicks that are to be the outcome of her three weeks' devoted labor of incubation. It is much more likely, however, that she is concerned about just eggs, being led by her blind instinct to follow this particular occupation, as she is led by instinct at a later stage to brood, protect, and provide food for her little flock, all of whom have their peculiar instinct to come at her call and to cuddle for warmth and safety under her protecting wings. Parental love emerges very gradually out of the blind instinctive performances by which animals are led to make provision for their eggs and young offspring. One of its earliest manifestations is in the instinct of protection. Ants, bees, wasps, and termites are pugnacious defenders of their nests. The male of the dogfish we have mentioned swims about for a time with his brood, and he guards them against enemies, but soon the little fishes

FIG. 123-Nestling marsh hawks. (After Baker.)

scatter and parental care vanishes. A mother bird, though naturally timid, will often bravely defend her young from attack; and among the mammals the mother with young is usually much more aggressive than she is under ordinary circumstances. Pugnacity toward outsiders goes along with increased solicitude for the safety of the dependent progeny, just as jealousy of rivals goes along with love of mates. Both love and animosity are woven into the conduct of animals in the interest of perpetuating their kind, and both have their uses.

Parental care in the birds comes to demand more and more of the energies of the individual as we pass from lower to higher

FIG. 124-Rufus crowned sparrow and young. The figure to the right shows the parent bird with food in its bill for the young. (From a photograph by J. Dixon.)

forms. The primitive birds usually lay many eggs in rather crude nests, and the young, which are hatched in an active condition, are soon able to make their own living. With the higher song birds there are often elaborately constructed nests nicely lined with soft downy feathers; few eggs are laid, and the young, which are hatched in an immature state, are tended with great care. Frequently the male and female parents take turns in feeding and protecting the young as they did in incubating the eggs. The excrement of the young, which is inclosed in a sort of membranous, gelatinous sack, is carefully removed by the parents. The period of active care is prolonged until after the

young birds are well feathered and are able to fly. Often one sees a nearly grown young robin begging food from indulgent parents who continue their ministrations after it is quite able to provide for its own wants.

An intimate association between mother and offspring is necessitated in the mammals by the circumstance that the young derive their sustenance from the mammary glands. The instinct of the young to suck, and the instinct of the mother to yield to the nutritive demands of her offspring, are correlated modes of behavior that extend throughout the whole class. As we pass from the lower to the higher mammals we find more care bestowed upon the offspring, and the period of association between parents and offspring comes to be lengthened. Among the higher mammals we meet with undeniable signs of true maternal affection. In the Descent of Man, Darwin remarks that "Rengger observed an American monkey (a Cebus) carefully driving away the flies which plagued her infant; Duvaucel saw a Hylobates washing the faces of her young ones in a stream. So intense is the grief of female monkeys for the loss of their young that it invariably caused the death of certain kinds kept under confinement by Brehm in N. Africa. Orphan monkeys were always adopted and carefully guarded by the other monkeys, both males and females."

Mr. John Fiske in his celebrated essay on "The Meaning of Infancy" has pointed out that the lengthening of this period of dependence affords an opportunity for the young to gain a richer and more valuable experience before embarking on the adventures of an independent career. As we pass up the scale of life, infancy becomes more prolonged; the young are born in a more helpless state; more effort is spent by parents upon their nurture, and more scope is afforded for the exercise of intelligence by the offspring in preparing for the exigencies of living. Successive generations thus become more closely tied together. At first the ties are mere blind instincts, but later they come to be those of affection manifested in the love of mates, the love of offspring, and finally a devotion to the larger social group. Gradually

the processes involved in the perpetuation of life have perfected as their final fruit the highest forms of human endeavor. But they all go to maintain the life process which, as Aristotle has remarked, has its end in itself.

REFERENCES

DARWIN, C. R., The Effects of Cross and Self Fertilization in the Vegetable Kingdom. N. Y., Appleton, 1876.

FISKE, J., The Meaning of Infancy. Boston, Houghton Mifflin, 1909. GEDDES, P., AND THOMSON, J. A., The Evolution of Sex. N. Y., Scribner, 1911.

HEGNER, R. W., The Germ Cell Cycle in Animals. N. Y., Macmillan, 1914.

HERRICK, F. H., The Home Life of Wild Birds. N. Y., Putnam, 1902. HOLMES, S. J., Studies in Animal Behavior (Chapters on "The Evolution of Parental Care" and "The Rôle of Sex in the Evolution of Mind"). Boston, Badger, 1916.

JENNINGS, H. S., Life and Death, Heredity and Evolution in Unicellular Organisms. Boston, Badger, 1920.

MARSHALL, F. H. A., The Physiology of Reproduction. London, Longmans, 1910.

MITCHELL, P. C., The Childhood of Animals. N. Y., Stokes, 1912. PYCRAFT, W. P., The Infancy of Animals. N. Y., Holt, 1913.

-, The Courtship of Animals. N. Y., Holt, 1914.

SUTHERLAND, A., The Origin and Growth of the Moral Instinct. 2 vols. London, Longmans, 1898.

CHAPTER XI

THE DEVELOPMENT OF SOCIAL LIFE

In the preceding chapter we have considered the multifarious activities connected with the perpetuation of life, from the fission of the simplest organisms to the development of parental care and the establishment of the family. The development of social groups in animals may be regarded as a continuation of the general course of evolution that we have briefly traced. Most students of social evolution in the animal kingdom hold that societies generally arose through the gradual expansion of the family. Social aggregates of animals are found in many very distantly related groups, and it must therefore be concluded that they have had many independent origins.

Before treating of societies as they are found in the social

insects and the higher birds and mammals, it will be instructive to consider briefly the colonial aggregates that occur among the lower invertebrates. Even the Protozoa, as we have seen, form colonies, and the same habit is common among sponges, hydroids, and many other groups. These aggregates of individuals are often called societies, and they exhibit many analogies with FIG. 125-Colony of the hydroid Podocoryne carnea: P, polyp; M, medusa the social organizations of free buds; S, protective hydroid. (After individuals among higher forms, Grobben.)

but it is perhaps best to call

them merely colonies, reserving the term society for an organized group of independent animals.