What Is the Rationale for Homogamous Mating?
Homogamy, defined by Murray (2012, p. 61) as the “interbreeding of individuals with like characteristics,” is also known as assortative marriage (Murray 2012; Schwartz and Mare 2005), or more commonly, assortative mating (Burley 1983) or assortative pairing (Figueredo and Wolf 2009). The like characteristics examined in Coming Apart are education and intellect. The highly educated paired off. The same seems to hold for intelligence. Sociocultural changes over the last 50 years have increased the ability to actualize educational and intellectual homogamy. First, a proportional increase in jobs demanding education and intelligence creates a market pressure for these increasingly valuable commodities. Second, the highly intelligent, being more valued, are then more efficiently and meritocratically separated from the general population through the college sorting machine. Elite institutions are attended, much more than previously, by the very smart. The very smart more routinely becomes the very educated. Thus, educational homogamy becomes more or less synonymous with cognitive homogamy. The cognitive elite attending prestigious colleges forms connections among themselves, meet and marry, jointly attend graduate schools, and thereafter find themselves at the same conferences and working the same jobs. Not only are elites pairing off in couples, they are forming communities. The resulting superzips, zip codes populated by the wealthy, educated and intelligent, become refugia, distinct in culture, class, and climate.
Educational and cognitive homogamy is part of a larger process of life history homogamy that is most directly studied in two articles by Wolf and Figueredo: Assortative pairing and life history strategy and Fecundity, offspring longevity, and assortative mating: Parametric tradeoffs in sexual and life history strategy. To understand such explanations of how life history drives mating patterns, it is important to pair the aforementioned distinction between intrinsic and extrinsic mortality with a general understanding of the function of sex (Smith and Maynard-Smith 1978). Large, long-lived organisms evolved sex as a weapon against Muller’s Ratchet and the Red Queen}1 The accumulation of deleterious mutations is controlled for by outbreeding. Then there are the pathogens and parasites, relentless sources of extrinsic mortality. The evolutionary speed of the short-lived microorganism could only be checked by sexual reproduction (Sherrat and Wilkinson 2009). Yet, sexual reproduction creates more than a unique immunological profile; it produces lineal diversity in risk acceptance, personality, dominance, and many of the life history variables discussed within this article, such as growth rate, age at first reproduction, and time orientation. This additional diversity is beneficial to the r strategy. War and unrest, famine and drought, immigration and emigration, along with parasite and pathogen pressure, bring unpredictability and risk, thereby selecting for the r strategy of procreating early and often with different individuals. The r strategist, having on balance more partners, is then less choosy about any particular partner; but more than this, the r strategist practices negative assortative mating, purposefully seeking dissimilarity, which, in turn, creates brood diversity. Brood diversity is desirable in that it is a beneficial hedge against unpredictable stressors. Again, this is not pathology. It is rather a rational response, and an evolved hedge against high extrinsic mortality that might otherwise kill the nulliparous young adult couple and the small, similar set of children (Figueredo and Wolf 2009).
The r strategist maximizes the recombinatory change of sexual reproduction, whereas the K strategist minimizes it. In contrast to the negative assortative mating of the r strategist, K strategists practice positive assorta- tive mating; they will more assiduously follow the dictates of genetic similarity theory12 (Rushton et al. 1984; Rushton 1990), mating with those similar on a variety of biological and cultural life history characteristics. Having been exposed to low extrinsic and high intrinsic mortality in their developmental histories and ancestral past, the K selected will mate in a manner that minimizes the recombinatory diversity natural to sexual reproduction13 and consequently produce offspring, fewer in number and more similar to one another (Figueredo and Wolf 2009). This is because “stable, predictable, and controllable environments put a selective premium on lower rates of genetic recombination to preserve the integrity of locally well-adapted, and perhaps co-adapted genomes” (Wolf and Figueredo 2011). In contrast to the r strategist that has no predictive power or coping mechanism to contend with high extrinsic mortality, the K strategist is the embodiment of a successful algorithm, capable of dealing with predictable and controllable intrinsic mortality. The latter will not look to scramble, but to preserve, their life history related variables by finding a like partner. The preference for the slow life history partner and the slow life history itself have become genetically intercorrelated (Figueredo and Wolf 2009; Wolf and Figueredo 2011; Olderbak and Figueredo 2010). In this light, the college sorting machine and its corollaries are vehicles, not simply for the creation ofintellectual, educational, and economic homogamy, but for life history homogamy; the college sorting machine actualizes the slow life history strategist’s inherent drive to mate with one another. When understanding intellectual, educational, and economic homogamy more broadly as life history homogamy, the urgency of Murray’s message is augmented by the knowledge that (1) life history traits have a moderate to strong heritable component; (2) form an intercorrelated complex; (3) are accompanied by a rational and genetic disposition to assortatively mate; (4) assortative mating is such a powerful evolutionary force that it can promote within species diversity within a population not isolated by distance (Wolf and Figueredo 2011).14