George Walford: Reality Over Rule
Any reader of anthropology (or at least any reader not committed to the conventions of the profession) will have been impressed, and perhaps puzzled, by the elaborate detail, precision and complexity of the kinship and marriage practices reported. One encounters phrases like this: ‘of the general type called Iroquois or bifurcate-merging, and of the particular subtype called Dravidian.’  The following passage comes from the opening pages of a discussion of kinship and descent, before the real complications begin to appear: ‘Different norms of cross-cousin marriage develop different configurations of interlineage alliance. Where matrilateral cross-cousin marriage sets in motion a direct current of women between lineages, the patrilateral form (father’s sister’s daughter marriage) establishes an alternating current.’ 
We have learnt not to underestimate the peoples studied by anthropology; there is no reason to think their potentialities less than our own. But accounts like this raise the suspicion that theory has gone into orbit. Has there ever been a time, anywhere, when people complied with marriage regulations of this precision and complexity? And has there ever been a place where, over generations, supply and demand maintained the necessary correspondence? Such doubts find support in the literature:
That the kinship classifications of a particular tribe may be out of joint with current social practices has been known from the beginning of kinship studies. Kinship terminology may have a life of its own, longer than the institutions which presumably gave rise to it. Moreover, social practices implying contradictory kinship classifications may co-exist in the same tribe. 
In the plains and forests as in the city streets, expediency comes first, with system, rule and principle tagging along behind.
Quotations from Sahlins, Marshall D. 1968 Tribesmen Englewood Cliffs N.J.: Prentice-Hall  69;  58;  69.
FIFTY-TWO centuries have elapsed since human beings first recorded their affairs in writing, and for thirty-five of these centuries there was a Pharaoh on the throne of Egypt. (John Ray).
from Ideological Commentary 56, May 1992.