It would be ungrateful not to acknowledge freely the service which McLennan and his adherents have rendered to the social history of mankind. They have brought to light a mass of very important facts which it is highly beneficial for us to know. It cannot be denied that wife-capture, exogamy, and the custom of taking kinship from the mother have very widely prevailed among primitive races. It is not so certain, however, that the right explanation of their origin or of their relation to one another has been given. In the first place, criticism, notably that of Herbert Spencer,[258] has detected fatal weakness and inconsistency in the argument by which Mr. McLennan has sought to establish his theory. It is doubtful, for instance, whether female infanticide has been so important a factor in social evolution.[259] But, granting that it has generally prevailed, it is hard to see how this would greatly disturb the "balance of the sexes." For "tribes in a state of chronic hostility are constantly losing their adult males, and the male mortality so caused is usually considerable. Hence the killing many female infants does not necessitate lack of women: it may merely prevent excess." McLennan's fundamental "assumption is therefore inadmissible."[260] Again it is held that female infanticide, "rendering women scarce, led at once to polyandry within the tribe, and the capturing of women from without." But "where wife-stealing is now practiced it is commonly associated with polygyny;"[261] while conversely, polyandry does not "distinguish wife-stealing tribes," such as the Tasmanians, Australians, Dakotas, and Brazilians. "Contrariwise, though it is not a trait of peoples who rob one another of their women, it is a trait of certain rude peoples who are habitually peaceful;" for instance, the Eskimo, "who do not even know what war is." Furthermore, if wife-capture and exogamy are at once practiced by a cluster of adjacent tribes, the scarcity of women would not be relieved. Inevitably the weaker tribes would "tend toward extinction;" and in the meantime, if a part only of their female infants were killed, they must deliberately "rear the remainder for the benefit" of their enemies.[262] Nor, as Starcke has pointed out, is there anything in a "scarcity of women which could lead a community accustomed to promiscuous intercourse to adopt polyandry; on the contrary, such a scarcity would make it more difficult to set limits" to promiscuity. "Marriage, or the exclusive possession of one woman by one or more men, would become more easy in proportion to the increase in the number of women, since the conflict between the lusts of the men would necessarily become less intense."[263] McLennan believes that exogamy has "been practiced at a certain stage among every race of mankind;" and that endogamy, or the custom of marrying within the kindred, is a "form reached through a long series of social developments."[264] Yet, inconsistently with this, he admits that