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The Paradox of Monogamy

This version was saved 11 years, 11 months ago View current version     Page history
Saved by Alex Backer, Ph.D.
on January 5, 2009 at 8:30:59 am

Monogamy seems maldaptive for a male from an evolutionary point of view: a male who simultaneously rears several children with multiple wives will have more descendants than one who must wait 1-2 years in between conceptions of his progeny. So why did monogamy evolve?


Polygyny (multiple wives at the same time) is allowed in 84% of human societies (Helen Fisher in Sternberg & Weis, p. 104). Only 10% of men practice it, but this is due to the mathematical fact that the number of women is approximately equal to the number of men, for reasons that are explained in another essay, and that 90% of men marry by age 50 in most cultures (Sternberg & Weis, p. 104). Romantic love typically lasts for a relatively short time (Sternberg & Weis), and attachment lasts through the period of child-rearing (Sternberg & Weis, p. 104). Worldwide divorce rates peak 4 years after marriage, approximately the inter-birth period, suggesting divorces exhibit the remains of an ancestral strategy for couples to remain together for the rearing of one child (Fisher, 1992, cited in Sternberg & Weis, p. 104).


(Permanent or serial) monogamy is aided by the biology of love. 


Falling is love is stimulated by novelty and danger. Given that love is the outcome of a mate selection process, perhaps danger signals that the time to be picky is over and you'd better get her pregnant before that dagger cuts through your heart. As for novelty, that may be driven by the same selective drive as the women's attraction toward partners with an immune system different from the woman's (Wedekind et al., 1995, cited in Sternberg & Weis, p. 102).


If love does not precede sex, it can follow it. The Nepalese say "Naso pasyo, maya basyo": The penis entered and love arrived. Sex is prone to make people, and particularly women, fall in love: seminal fluid contains dopamine and tyrosine, a precursor of dopamine. Sex can also stimulate attachment via orgasm, which releases oxytocin and vasopressin (Sternberg & Weis, p. 103).


So (serial) monogamy follows from the sex ratio: given the mathematics that allow the average man to be with only one woman at a time, monogamy ensures that the man next to any given woman is the one most likely to have fathered her children, which maximizes the incentive for paternal participation in child-rearing.



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