Bateman's principle holds that due to having more parental investment, females tend to reproduce 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 also simply means men had more variance in reproductive success. Moreover, the latest large study from 2016 testing the hypothesis did find a significant effect across many animal species, including humans.
Bateman's principle in humans[edit | edit source]
In humans, there are number of mechanisms are involved in the Bateman's principle, all deriving from differential parental investment. There are even feedback loops involved which reinforce the sexual dimorphism in reproductive variance:
- Females have greater parental investment for a number of reasons:
- The production of eggs is more expensive than the production of sperm.
- By virtue of having a womb, reproducing is physically risky for women (in particular due to the large human head). Maternal mortality rate used to be 10 times has high as in modern societies. Women may also have a few years shorter fertile lifespan as giving birth requires youthful health. This implies also older men compete for the few fertile young women, further aggravated by the fact that youngest women are the least likely not to have had already children, that the man would have had to provide for.
- Sex is also riskier for women as the pocket shape of the vagina is more vulnerable to STDs.
- The offspring has higher dependence on the mother as the mother but not the father is guaranteed to be present at birth, and babies depend on women's breastmilk. Human offspring is also one of the most dependent offspring of all animals due to the complex socialization process and slow brain development that allows for higher intelligence.
- For these reasons, females have lower expected lifetime reproductive success, so each of the few offspring needs to be held to higher standards than men's. This makes women more choosy and coy.
- Men, on the other hand, can produce millions of sperm cells with little cost and can get away with reproducing with lots of females, not needing to care for the offspring as much. Men have not much to lose carelessly pumping and dumping many, potentially low-quality women, except for catching STDs. Men can even brag about many sex partners, even if of low quality, as men are chosen based on their status (which itself is a result of Bateman's principle as pointed out below). (Though in some cultures they can also lose reputation, but arguably not much.)
- Conversely, women cannot brag about this since women form pussy cartels and shame free sex to avoid losing control over men. Women also compete in a reputation of faithfulness since men desire certainty about their fatherhood. Women's intrasexual competition is also harsher because women have not as much to gain from cooperation as men. Men face an trade-off between high and low investment, whereas women primarily want high investment from men, except when there is a prospect of copulating with a very attractive man (to get sexy sons). Not being able to brag about having sex arguably contributes to inhibiting women's libido.
- Promiscuous men of low quality, in turn, cause women to be even more coy, exaggerating the effect.
- Women are hence the limiting factor in reproduction rate, men need to compete for status in order to gain copulation opportunities.
- This, in turn, gives women more options to choose from, so they can also afford to be extra choosy, exploiting their privilege much like a parasite.
- Finally, the greater number of sexually available males allows women to reproduce much more reliably, whereas few (alpha) males have a disproportionally high reproductive success (Bateman's principle). Hence women's strategy is slow life history, and men's strategy is faster.
All of these factors that drive women's evolution toward slow life history are counterblanced by the need to actually reproduce. Women also face a trade-off between sexualizing themselves to attract higher-status males and avoiding gaining too much of a reputation for sluttiness.
Implications[edit | edit source]
The differential parental investment can explain a wide variety of phenomena:
- 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.
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]
- 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.