Bateman's principle holds that due to greater parental investment, females tend to produce fewer offspring than males, but reproduce more reliably. Conversely, a few males have lots of offspring, but some males produce none. This means males have more variance in their reproductive success.
There is debate as to whether this principle holds true across the animal kingdom as a whole, or only under certain conditions in some species, however the principle does hold for 94% of human societies that were considered in a 2009 study, as well as for a variety of other species like birds and even certain kinds of fungi. Analyses of diversity of exclusively male and female parts of the DNA also show that women reproduced around twice as often as men which provides evidence men had more variance in reproductive success throughout human history. Moreover, a large study from 2016 did find a significant effect across many animal species, including humans. In traditional societies, men’s reproductive variances were estimated to be approximately 2–4 times those of women, and in the average forager society, 21% of married women are married polygynously.
Bateman's principle in humans[edit | edit source]
Women have greater parental investment, or more broadly a greater cost associated with reproduction, for a number of reasons:
- The production of eggs is more expensive than the production of sperm.
- Pregnancy is metabolically costly and long.
- Pregnancy and birthing is risky due to the large human head and high birth weight relative to the mother's body size.
- The pocket shape of the female reproductive organ is more vulnerable to STDs.
- The offspring has higher dependence on the mother as only the mother is guaranteed to be present at birth and babies depend on women's breast milk.
- Human offspring is one of the most dependent offspring of all animals due to the complex socialization process and slow brain development that allows for higher intelligence and women were historically much more involved in raising the offspring than were men.
For these reasons, females have lower expected lifetime reproductive success and a lower life history speed, so each of the few offspring is held to higher standards than men's. This makes women more choosy, passive and coy, meaning they defer sex. Men, on the other hand, can produce millions of sperm cells with little cost and can afford to carelessly impregnate many females (promiscuity), not needing to care for the offspring as much. Men have not much to lose pumping and dumping even low-quality women, barring STDs and embarrassment, but can gain opportunities for increasing their representation in the future gene pool, as well as increasing genetic variation of their offspring and increasing the chance that some offspring will survive and have high sexual success. This makes men constantly horny with relatively much lower/promiscuous mate choice standards (except when they marry, i.e. invest their resources, in which case they are also very choosy).
The greater number of sexually available men allows women to reproduce much more reliably, whereas few (alpha) males have a disproportionally high reproductive success. Since women are the limiting factor in reproduction (have a slower life history), men need to compete for status in order to secure copulation opportunities.
There may be feedback effects that further reinforce Bateman's principle:
- Promiscuous low-quality men cause women to be even more coy, which further decreases their reproductive variance.
- Promiscuous men also give women more options to choose from, so they can also afford to be extra choosy in line with their overall sneakiness.
- As men are overall held more responsible and as they compete more (e.g. by bragging about sex), they also are also much more subjected to Matthew effects, meaning the experience of downward or upward spirals which may further increase reproductive variance.
Related phenomena[edit | edit source]
Differential parental investment can explain a wide variety of phenomena besides sex difference in reproductive variance:
- More parental investment means women have slower life history speed (LH), so their strategy is to only have high quality sex and late, and men's strategy is fast LH, meaning lots of sex and early. These sex differences have been found across 53 nations.
- The resulting differences in activity level and competitiveness for reproductive opportunities implies that men have a high reproductive variance and women a low one, meaning men are more of a gamble, a high-risk/high-reward strategy. A result is that animals with pronounced differential parental investment evolve to produce more offspring in ecologically mild conditions to exploit potential high-reward of males, and to produce more female offspring in harsh conditions to ensure reproduction (Trivers-Willard hypothesis). Evidence of this in humans is for example billionaires having more male offspring.
- The existence of hypergamy, i.e. the tendency that women prefer men of higher education, social or economic status, as a particular instance of choosiness and women's need to secure resources for their offspring.
- Why most historical achievements were done by men: Men, but not women, are biologically required to compete.
- Why humans are moderately polygynous across many cultures. 85% of all cultures have allowed polygyny to occur.
- Why women are regarded as more valuable (women-are-wonderful effect) and men as more disposable.
- Why women wait longer before having sex, namely to await better options and test their partners.
- Why women switch mates, initiate divorces and become disinterested in sex sooner than men.
- Why women more likely regret sex and relationships.
- Why men have a higher cumulative demand for sex and hence why males experiencing inceldom outnumber females experiencing inceldom, e.g. social psychologist Roy Baumeister wrote about the Tragedy of the Male Sex Drive:
Given the mismatch between men's and women's desires, most men are doomed to experience chronic sexual frustration. […] [Men] are doomed to be horny.
Increased sex imbalance[edit | edit source]
Academics such as scholar Angela Nagle and sexologist Kristin Spitznogle, and others such as Roger Devlin argue that imbalance in reproducive success has intensified recently, largely a result of female sexual liberation.
A study which analyzed GINI coefficients in number of sexual partners found that, "single men have a higher Gini coefficient (.536) than single women (.470). Thus, female sexual partners are more unequally distributed among single men than male sexual partners are among single women."
A study that analyzed changes in the distribution of sex partners from 2002 to 2011-2013 showed that compared to 2002, top 20% of men (in terms of LMS) now had a 25% increase in sexual partners, and the top 5% of men had an outstanding 38% increase in the number of sexual partners. The study commented that “no significant changes were identified among women in the top 20% and top 5%, overall, and among subgroups”.
While the rate of the sexless in the U.S. has increased for both men and women in the recent decades, it has increased more for men than for women.
The largest increase of sex imbalance has been observed in Finland, which is a very sexually liberal country and may be similar to liberal subcultures in other countries.
References[edit | edit source]
- Brown, G.R., Laland, K.N. and Mulder, M.B. 2009. Bateman's principles and human sex roles. [FullText]
- Janicke, T., et al. 2016. Darwinian sex roles confirmed across the animal kingdom. [Abstract]
- Brown, Laland, & Borgerhoff Mulder, 2009
- Marlowe & Berbesque, 2012
- https://doi.org/10.1177/1754073917709940 (Al-Shawaf 2017)
- https://www.ncbi.nlm.nih.gov/pubmed/17975724 (Lippa 2009)
- Baumeister, R.F. and Bushman, B., 2010. Social psychology and human nature, brief version. Nelson Education.