Besides food, however, there is a second elemental condition which vitally affects the human race; and that is sex.  Social organization thus comes to have a twofold aspect.  On the one hand, and perhaps primarily, it is an organization of the food-quest.  On the other hand, hardly less fundamentally, it is an organization of marriage.  In what follows, the two aspects will be considered more or less together, as to a large extent they overlap.  Primitive men, like other social animals, hang together naturally in the hunting pack, and no less naturally in the family; and at a very rudimentary stage of evolution there probably is very little distinction between the two.  When, however, for some reason or other which anthropologists have still to discover, man takes to the institution of exogamy, the law of marrying-out, which forces men and women to unite who are members of more or less distinct food-groups, then, as we shall presently see, the matrimonial aspect of social organization tends to overshadow the politico-economic; if only because the latter can usually take care of itself, whereas to marry a perfect stranger is an embarrassing operation that might be expected to require a certain amount of arrangement on both sides.

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To illustrate the pre-exogamic stage of human society is not so easy as it may seem; for, though it is possible to find examples, especially amongst Negritos such as the Andamanese or Bushmen, of peoples of the rudest culture, and living in very small communities, who apparently know neither exogamy nor what so often accompanies it, namely, totemism, we can never be certain whether we are dealing in such a case with the genuinely primitive, or merely with the degenerate.  For instance, the chapter on the forms of social organization in Professor Hobhouse’s Morals in Evolution starts off with an account of the system in vogue amongst the Veddas of the Ceylon jungle, his description being founded on the excellent observations of the brothers Sarasin.  Now it is perfectly true that some of the Veddas appear to afford a perfect instance of what is sometimes called “the natural family.”  A tract of a few miles square forms the beat of a small group of families, four or five at most, which, for the most part, singly or in pairs, wander round hunting, fishing, gathering honey and digging up the wild yams; whilst they likewise take shelter together in shallow caves, where a roof, a piece of skin to lie on—­though this is not essential—­and, that most precious luxury of all, a fire, represent, apart from food, the sum total of their creature comforts.