Evidence That Sex Ratios Have Long Impacted Male/Female Mating Behaviour
[…] low sex ratios at couple formation ages existed in the U.S. between 1965 and the early 1980s. The currently high sex ratios, however, will persist until the end of the century. High sex ratios appear to be associated with lower divorce rates, male commitment to careers that promise economic rewards, male willingness to engage in child care, higher fertility, and higher rates of sexual violence. Sexual selection theory calls attention to intrasexual competition in the numerically larger sex.
Secular trends in human sex ratios : Their influence on individual and family behavior
This finds that, after WWII and beginning in 1965, single men began to outnumber single women in the U.S., leading to a relatively excess of men. More men are now living throughout the entire reproductive age bracket. The same phenomena was observed in England and Wales in the 90s:
Partner supply in Britain and the US: estimates and gender contrasts
When men are scarce in a female-biased population, there is less incentive for competition among men for relationship commitment and paternal investment because male scarcity enhances their short term mating success. Females thus have less selective power and may exhibit lower thresholds for male commitment in order to have sexual relations:
Across history, female biased Operational Sex Ratios (OSRs) tend to destabilize marriages and lead to higher divorce rates, more out-of-wedlock births and single mother households, and lower paternal investment. Male biased OSRs are associated with the reverse pattern.
Male Scarcity is Differentially Related to Male Marital Likelihood across the Life Course
In the U.S., black Americans have continued to have a low sex ratio among individuals of reproductive age (because of high male mortality, high male incarceration, and low sex ratio at birth). Marriageable black women thus tend to outnumber black men:
The Divergance of Black and White Marriage Patterns
In accordance with this lower sex ratio, African Americans have a lower rate of marriage and higher rate of marriage dissolution. In a large cross-cultural analysis comparing 70 countries it was found that societies with low sex ratios had less paternal investment and marital stability:
The Sex Ratio as a Predictor of Cross-National Variation in Violent Crime
The preponderance of single men to single women (in the West) persists to this day and shows no signs of declining. There are also economic implications for male-biased sex ratios:
Male-biased sex ratios (an abundance of men) lead men to discount the future and desire immediate rewards. Male-biased sex ratios decreased men’s desire to save for the future and increased their willingness to incur debt for immediate expenditures. Sex ratio appears to influence behavior by increasing the intensity of same-sex competition for mates. Accordingly, a scarcity of women led people to expect men to spend more money during courtship, such as by paying more for engagement rings.
The Financial Consequences of Too Many Men: Sex Ratio Effects on Saving, Borrowing, and Spending
- Figure 1. (of this post) shows the correlation between sex ratio and sociosexuality (promiscuity):
As displayed in Figure 1, cultures with more men than women are more sociosexually restricted than cultures with more women than men. […] Thus, the cultural test cases of the ISDP appear to fit well within sex ratio theory as posited by Pedersen (1991).
Sociosexuality From Argentina to Zimbabwe: A 48-Nation Study of Sex, Culture, and Strategies of Human Mating
“Pedersen (1991)” refers to the first study of this post. As can be seen in the figure, low sex ratios and high sociosexual levels are evident in the Baltic nations of Estonia, Latvia, and Lithuania, implying that the females there will appeal more strongly to the male ideal because the number of marriageable men in Latvia is low relative to the number of women. Males have higher sociosexuality scores than females but sociosexuality scores for females vary widely across countries. Continued:
[…] in Figure 1, it appears that once women begin to outnumber men at a sex ratio of about 95, the national level of sociosexuality becomes especially accentuated. […] Low sex ratios in the Baltics are not surprising given the high rates of male suicides and deaths from accidents within these nations (e.g., Neumayer 2003). However, even without the Baltic nations, the correlation between sex ratio and sociosexuality was significant, r(43) = -0.38, p < .01. These findings are consistent with the view that cultures with more women than men possess mating systems driven via the powers of sexual selection by men’s evolved desires for unrestricted, promiscuous sex. Figure 1 also shows that cultures with more men than women (e.g., Hong Kong, Bangladesh, and Taiwan) tend to be low on sociosexuality. In these cultures, according to sex ratio theory, the mating system is driven by women’s more potent desires for longterm, monogamous mating.
The sex differences in mating patterns, particularly the differences in short-term mating strategies, i.e., how men and women go about being promiscuous—men opt for large numbers/variety and women focus on quality—are found to be culturally universal throughout the world: Findings from a cross-cultural survey of 52 nations, 6 continents, and 13 islands find the same sex differences were evident regardless of whether mean, median, distributional, or categorical indexes of sexual differentiation were evaluated. Further studies have replicated these findings.
- The Heritability of Sociosexuality (Promiscuity)
Finally, and perhaps most importantly, is that a bulk of influence from genes impacts individual outcomes on seemingly any measure of traits, and this includes individual promiscuity, as assessed by an Australian twin registry study:The figure above shows the estimates for the genetic (A), shared (C) and unique environment (E) influencing sociosexuality. About half the influence impacting individual promiscuity is a result of genes:
[…] Although men are substantially more interested than women in casual sex, there is ample variation in this trait (sociosexuality) within both sexes. […] A competing theory is that children acquire their mating strategy after observing their parents’ relationship. […] Parental marital instability was modestly associated with sociosexuality, but this could have been due to either genetic or environmental factors. Consistent with genetic theory, familial resemblance appeared primarily due to additive genetic rather than shared environmental factors.
Interestingly then, the causes and correlations of individual differences in sociosexuality appear to actually be similar in men and women. Demographic variables did not interact with sex in the prediction of sociosexuality. E.g., how males may behave in female-biased OSRs is impacted by genes and the unique environment. If taken in the weaker sense, some men will forgo monogamous mating if given the option, this appears to be partially true, but this is largely moderated by genes.
- Along with individual differences, there exist differences at the group level. Associations are found between a dopamine receptor D4 (DRD4) gene variant (7R+) with both infidelity and sexual promiscuity. For one, African-Americans are found to posses significantly more of these 7R alleles. Continued here.
Moreover, sex ratios, and the subsequent male/female-driven sexual selection they produce, serve a significant place in human evolutionary history: