Matrilineal inheritance: New theory and analysis

Abstract

In most cultures, extramarital sex is highly restricted for women. In most of those cultures, men transfer wealth to their own sons (patrilineal inheritance). In some cultures extramarital sex is not highly restricted for women, and in most of those cultures, men transfer wealth to their sisters' sons (matrilineal inheritance). Inheritance to sisters' sons ensures a man's biological relatedness to his heirs, and matrilineal inheritance has been posited as a male accommodation to cuckoldry—a paternity strategy—at least since the 15th century. However, longitudinal analysis of the cumulative effect of female extramarital sex indicates that matrilineal inheritance is most advantageous for women and would be more accurately considered a grandmaternity strategy. That is, if the probability that men's putative children are their biological children (ρ = probability of paternity) is less than 1, the probabilistic degree of relatedness between a female and her matrilineal heirs is higher than her corresponding relatedness to her patrilineal heirs. The same holds true for men only if ρ is very low (< 0.46). The upshot is that for moderate levels of female extramarital sex, matrilineal inheritance, relative to patrilineal inheritance, is highly advantageous for women and disadvantageous for men. Consideration of female variance in reproductive success beyond the first generation, and of a man's network of obligation to the inclusive fitness of his relatives, suggests that although the establishment of matrilineal inheritance may require extremely high levels of female extramarital sex, once established, it is likely to be maintained at levels of ρ that reasonably characterize many societies in the ethnographic record. New analysis of previously published data shows a strong association between matrilineal inheritance and moderate to low probability of paternity, and an even stronger relationship between patrilineal inheritance and high probability of paternity.

Matriliny as daughter-biased investment

“…This calculation takes into account the impact of P on the probability that a man and his sister have different fathers. Hartung (1985) suggested that matrilineal inheritance might be an adaptive long-term male strategy, because over several generations a man's probabilistic relationship to his patrilineal descendants decreases geometrically as P is multiplied each generation. If P < .725, then a man's probabilistic relationship to his great grandson is lower than his probabilistic relationship to his third generation matrilineal heir.…”

“…As an alternative hypothesis, Hartung (1985) suggested that matriliny might be a grandmaternal strategy -investing in daughters' children. This is adaptive for grandmothers if there is any degree of paternity uncertainty (if P < 1.0, which is probably true in virtually all societies).…”

“…Using ethnographic evidence such as the reported frequency of adultery and divorce in 288 societies worldwide, Flinn (1981) found that matrilineal societies generally have low levels of paternity confidence compared to patrilineal societies. Other comparative studies have also found that matriliny is associated with low paternity confidence (Gaulin & Schlegel, 1980;Hartung, 1981Hartung, , 1985. Quantitative genetic studies comparing levels of nonpaternity in patrilineal and matrilineal societies remain to be done.…”

“…Men transmit wealth and political rights to their sisters' sons. From an evolutionary perspective, matriliny presents a puzzle, because men are only half as related to their sisters' sons as to their own sons (Alexander, 1974;Greene, 1979;Hartung, 1981Hartung, , 1985. This conflicts with the prediction of kin selection theory that, given equal costs and benefits, altruism will be directed towards relatives with the highest relatedness, usually offspring (Hamilton, 1964a(Hamilton, , 1964b.…”

“…We present data on wealth, sex, and reproductive success (RS) in two African societies, one patrilineal and one matrilineal, which support the daughter-biased investment theory. Daughter-biased parental investment has received little attention in the matrilineal literature, either in the classic ethnographic studies (Richards, 1950;Schneider & Gough, 1961) or in more recent evolutionary analyses (Flinn, 1981;Gaulin & Schlegel, 1980;Hartung, 1981Hartung, , 1985, which focussed almost exclusively on male political rights and inheritance. The Ethnographic Atlas, a cross-cultural database of 1267 cultures, does not even include a code for wealth inheritance to daughters; only 4 societies (0.3%) are noted as having mother to daughter land inheritance, compared to 163 (13%) with matrilineal descent (Murdock, 1967).…”