Remember that by the law of exogamy, the father and mother are strangers to each other.

Hence, primitive society, as it were, issues a judgment of Solomon to the effect that, since they are not prepared to halve their child, it must belong body and soul either to one party or to the other.
We may now go on to analyse this one-sided type of kinship-organization a little more fully.

There are three elementary principles that combine to produce it.

They are exogamy, lineage and totemism.

A word must be said about each in turn.
Exogamy presents no difficulty until you try to account for its origin.
It simply means marrying-out, in contrast to endogamy, or marrying-in.
Suppose there were a village composed entirely of McIntyres and McIntoshes, and suppose that fashion compelled every McIntyre to marry a McIntosh, and every McIntosh a McIntyre, whilst to marry an outsider, say a McBean, was bad form for McIntyres and McIntoshes alike; then the two clans would be exogamous in respect to each other, whereas the village as a whole would be endogamous.
Lineage is the principle of reckoning descent along one or other of two lines--namely, the mother's line or the father's.