One of the difficulties that has met me in my studies of the family among the animals is that, as we ascend the scale of life, there is a moral retrogression in fatherhood—at least, that is how it appears to me. There are, as far as I have found, no examples among mammals, the highest and last group of the animal kingdom, of devoted fathers undertaking the sole charge of the young, and few where the father even shares with the mother to any extent in the work connected with the upbringing of the family. The egoistic desires seem to increase in the males, with a corresponding weakening of their interest in the family and willingness to participate in its duties. The young are carried by the mother alone, they are protected chiefly by her; the father takes no part in the nursery cares, and rarely does he help in providing food for the children. The family is maternal, the female—the mother—its centre; the male is bound sexually to the female, but apart from this his connection with the family is slight; we find him most frequently following personal interests. In contrast with the conduct of the fathers in the families we have so far examined among the birds, reptiles, fishes and insects, with whom the father’s solicitude and sacrifice for the young equals and, in some cases, rivals that of the mother, this complete paternal indifference is really very startling. It demands our attention. What factors have brought about this reversal, which at first sight appears so strange? Why is it that the parental instinct diminishes in the father and is now fixed in the mother? It is, however, easy to understand this change if we consider what now happens, and the changed conditions under which the young are born. The mammals do not lay eggs like bird and reptile mothers, but each mother retains the eggs within her body, and so secures for the young warmth and protection far more certainly than would be possible in the best-contrived nest or home.[47] But this has led to changed habits. No nest or brooding-home has to be made, and the same preparations for the family, which hitherto have united in work the father with the mother, are unnecessary. Again, food has not now to the same extent to be collected and stored in readiness for the future needs of the children. The embryo, living within the body of its mother, gains the food for its growth directly from her blood. The connection between mother and child now is closer; her condition and health become of direct importance for the welfare of the young. At the same time the importance of the father is sharply lessened. This is plain. The early stages of mother-care, instead of being conscious and external acts regulated by special circumstances and often modified to meet different needs, now become part of the unconscious functions of the body of the mother—the child is an extension of herself. The advantage to the offspring of this change from external to internal protection