Evolution of monogamous marriage by maximization of inclusive fitness

Abstract

The majority of human societies allow polygynous marriage, and the prevalence of this practice is readily understood in evolutionary terms. Why some societies prescribe monogamous marriage is however not clear: current evolutionary explanations—that social monogamy increases within‐group co‐operation, giving societies an advantage in competition with other groups—conflict with the historical and ethnographic evidence. We show that, within the framework of inclusive fitness theory, monogamous marriage can be viewed as the outcome of the strategic behaviour of males and females in the allocation of resources to the next generation. Where resources are transferred across generations, social monogamy can be advantageous if partitioning of resources among the offspring of multiple wives causes a depletion of their fitness value, and/or if females grant husbands higher fidelity in exchange for exclusive investment of resources in their offspring. This may explain why monogamous marriage prevailed among the historical societies of Eurasia: here, intensive agriculture led to scarcity of land, with depletion in the value of estates through partitioning among multiple heirs. Norms promoting high paternity were common among ancient societies in the region, and may have further facilitated the establishment of social monogamy. In line with the historical and ethnographic evidence, this suggests that monogamous marriage emerged in Eurasia following the adoption of intensive agriculture, as ownership of land became critical to productive and reproductive success.

Men’s status and reproductive success in 33 nonindustrial societies: Effects of subsistence, marriage system, and reproductive strategy

“…These factors include low variance in men's mate value (71,72), higher percent contribution by men to household diet (73), dilution of wealth transmission across generations (74), and a male-biased operational sex ratio (75,76). In populations where operational sex ratios are male biased, men may derive more value from status as a means of maintaining an existing mate than as a means of acquiring new mates (75), or at least more so than in populations where operational sex ratios are female biased.…”

Property and wealth inequality as cultural niche construction

“…Harris [46, p. 132] suggests that this may have been a device invented by wealthy families to reduce the effects of partibility. These societies were also socially monogamous and Fortunato & Archetti [5] have shown that social monogamy can be a stable strategy reproductively advantageous to males where division of resources leads to a loss of their value, or where wives provide greater paternity certainty in exchange for exclusive transmission of wealth to their children. This is the reason, they argue, for the prevalence of monogamy in the historical societies of Eurasia because they were based on intensive agriculture in conditions of land scarcity, so that landownership provided a major productive and therefore reproductive advantage.…”

“…Dowry with monogamy represents the most probable ancestral state at the root of the Indo-European tree and a statistical analysis of the most probable evolutionary path from this state shows that bridewealth with polygyny and dowry with monogamy represent relatively stable configurations whereas the converse combinations do not. As we have seen, monogamous marriage can be a stable strategy reproductively advantageous to males where division of resources leads to a loss of their value, or where wives provide greater paternity certainty in exchange for exclusive transmission of wealth to their children [5]. A connection between such postulated practices and early farmers in Europe is suggested by recent estimates of the date of the root of the Indo-European language tree to between 8000 and 10 000 years ago [68], which potentially links their spread to the spread of farming and farmers [69].…”

The evolution of matrilineal kinship organization

“…Fortunato & Archetti [20] developed a game-theoretic framework to investigate the interplay between behavioural strategies relating to marriage, property transfer and level of paternity. Addressing the question of the evolution of monogamous marriage, they showed that this marriage strategy may be advantageous over polygynous marriage because it 'concentrates' resources in a limited number of heirs.…”