Group survival being the fundamental thing, the group is obliged to develop a division of labour which directs the activities of the individuals composing it to providing for its necessities, regardless of any interference with their own desires. That is, if group survival requires that woman use her specialization to child-bearing instead of any adaptation she may possess in other directions, one of two things inevitably result: (1) Either the group finds or evolves some social control machinery which meets the necessity, or (2) it must give way to some other group which can do so. In either case, the result is a division of labour, which we see more clearly in primitive peoples. The less efficient group is not necessarily exterminated, but if it loses out in the competition until some other group is able to conquer it and impose _its_ division of labour the result is of course the extinction of the conquered group as an integral part of society. This is simply natural selection working on groups. Natural selection works chiefly in this manner on the human species, _because that species lives in groups_. Such group control of the component individuals as has been described has led to a division of labour between the sexes in every primitive society. All this means is that the group adopting such a division has greater survival value, and hence is more likely to be represented in later ages. It must not be supposed that such systems of control were always logically thought out or deliberately planned. Even animals which live in herds or colonies have divisions of labour. Through an infinite slaughter of the least fit, such groups arrive at some kind of instinctive adjustment to produce and protect the young. The crudest human intelligence must have eliminated much of the waste involved, by comprehending obvious cause-and-effect relations which animals have to arrive at through trial and error methods. For example, an intelligence capable of employing artificial weapons is also able to see that the wielder of these for group defence cannot be encumbered with baggage or children when the group is in movement. Hence women became the burden bearers, and took care of the children, even after the nursing period. War parties could not generally be mixed, for the obvious reasons that such women as did not have young children would be pregnant a good deal of the time, or likely to become so. Moreover, a hunter and fighter must not have his courage, ferocity and physical initiative undermined by unsuitable employments and associations.