Body Count: Much More Than You Wanted To Know

Body count discourse is on par with race as one of the most toxic topics to discuss on social media. This is because the discussion of the issue is linked to some sacred cows (e.g. women’s liberation, religion), and discussing sacred things tends to lead to emotional discussions instead of rational ones. As far as I can tell, body count discourse involves the two main questions:

1. Is somebody’s body count indicative of certain character traits?

2. Do high body counts cause people to have bad relationships or mental health problems?

In terms of correlative research, an individual’s number of sexual partners is linked to risk of divorce (Smith & Wolfinger, 2021; Wolfinger, 2016). In addition, promiscuity is also linked with poorer mental health in young adults (Bersamin et al., 2014; Johnson, 2003) and lower levels of marital happiness (Wolfinger, 2018; Willoughby et al., 2023). All of these relationships are fairly weak - the correlation between body count and well-being is only -.2. Even making some generous assumptions about the reliability of self-reports, it’s unlikely that the true relationship is stronger than -.4.

While in most cases these relationships are linear, this is not the case for divorce. For divorce rates, the highest rates were observed in those who had 2 or more than 10 premarital partners, and the lowest rates were observed in those with 0 or 1 premarital partners. This suggests some degree of confounding, as most of the hypothesized mediators in this relationship (decreased pair bonding ability, STDs, premarital births etc.) should be linearly related to chances of getting divorced.

While the debate surrounding body counts seems to focus solely on women, what’s interesting is that these associations are also observed in men (Wolfinger, 2018; Smith & Wolfinger, 2021), and that women are also aversive to promiscuous partners (Cook & Cottrell, 2021; Stewart-Williams et al., 2016; Marks & Fraley, 2005).

I think that the discussion about sexual partners focuses on women because it is more politically relevant to police the promiscuity of women. First, they are more sensitive to social exclusion (Hanson, 2023), so shaming them will have a greater impact on their behaviour. Second, they are the ones who tend to decide when sex happens in a relationship (Cohen & Shotland, 1996), so their choices are the ones that influence the amount of sex that occurs in a society. 

While it is clear that people with high body counts tend to have slightly worse personalities and relationship outcomes, it’s not clear whether they are causing them. Besides simple causation from body count to outcome, there are several theories as to why this relationship could exist:

1. People who are mentally unstable have problems connecting with other people and flunk out of relationships more often, so they have more sexual partners.

2. Large amounts of sexual partners makes you more mentally ill, which causes other negative outcomes such as relationship dissatisfaction and marital instability. 

3. A person’s pair bonding ability diminishes with every significant sexual encounter.

The way to test this is pretty straightforward - observe whether body counts are associated with unfavorable outcomes after controlling for traits such as mental health, personality, and attitudes about sex using regression analysis. I have one problem here - I have not found a single study that evaluates the relationship between your number of sexual partners and getting divorced controlling for personality or genetics, so there is no definitive evidence in favor of causality or against it. 

It is also important to avoid controlling for mediators - that is, if promiscuity causes mental illness, controlling for mental illness when evaluating the relationship between promiscuity and divorce would not be acceptable. This would be analogous to researching the causal association between getting shot at and dying independent of bullets piercing your organs. Because of this, it is important to know whether promiscuity causes depression and/or mental instability before doing any other analysis. Francis Black (2022) has already examined this topic, and he concluded that the number of sexual partners is not causally associated with mental health.

This is because the association between poor mental health and promiscuity is not observed within twins (Deutsch & Slutske, 2014), and is not consistent with the theory that casual sex causes mental health issues. Here is a segment of the abstract, for those interested:

Multilevel models that measured within-twin and between-twin pair effects of adolescent casual sex were estimated, using 714 twins (357 twin pairs) from the sibling subsample of the National Longitudinal Study of Adolescent Health (Add Health). Results indicated that there was no causal relationship between casual sex in adolescence and higher levels of depressive symptoms or suicidal ideation in young adulthood, and these effects did not differ by gender.

Not the greatest sample size, but fortunately there is more research that used sibling pairs instead of twins (Mendle et al., 2013), which mostly replicate those findings:

Using data on 1,551 sibling pairs (ages 13-18) from the National Longitudinal Study of Adolescent Health, the current study utilized a sibling comparison design to assess whether adolescent dating, sexual intercourse with a romantic partner, and sexual intercourse with a nonromantic partner were associated with higher levels of depressive symptoms independent of familial factors. Results indicated that adolescent dating, in and of itself, was not associated with depressive symptoms. The association between depressive symptoms and sexual activity with a romantic partner was fully accounted for by between-family genetic and shared environmental confounds. In contrast, sexual activity with a nonromantic partner was significantly associated with both mean levels of depressive symptoms and clinically severe depression, even within sibling dyads.

While they did report a significant association between depressive symptoms and having sex within siblings, the effect was reduced by 43% after controlling for genes and shared environment, which is quite a bit, given that the kinship coefficient of two siblings is only 0.5. Most notably, if you look at the within families effects, having sex is associated with about as much depressive symptoms as dating is.

Some people may argue that this approach ignores the female-male difference in responses to casual sex. Men generally feel more self-confidence and satisfaction after casual sex, while women tend to report more loneliness and rejection (McKeen et al., 2022). There is one problem here - the link between poor mental health and number of sexual partners appears in men as well (Bersamin et al., 2014), so the emotions that casual sex causes in the short term probably don’t translate to the long term. 

While it is fairly certain that sexual experience with multiple people does not cause mental health problems, it still isn’t clear whether the relationship between the number of sexual partners and relationship difficulties is causal. 

From what can be observed, the theory that promiscuity makes pair bonding more difficult has not been falsified or confirmed. 

Alexander (2022) wrote a post on his blog against the hypothesis that promiscuity inhibits pair bonding - the most relevant argument against it being that humans tend to be serially monogamous, so a biological mechanism which makes promiscuous behaviour inhibit pair bonding would not be adaptive. He contrasts humans with prairie voles to illustrate this - voles will lose the will to live if they are separated from their lifelog partners, which is not the reaction that is observed in humans. He also notes that recent human sexual behaviour, but not past sexual behaviour, predicts pair-bonding - which is reasonable evidence against the hypothesis.

I think this take lacks nuance - humans are obviously less monogamous than prairie voles, but they do mentally suffer from relationship break ups all the same. Life history and mating strategies also vary substantially within humans and their societies. In George Murdock’s ethnographic atlas of 1231 societies, 186 are strictly monogamous, 453 of them were mainly monogamous, 588 were mainly polygynous, and 4 had polyandry (Gray, 1998). To be fair, this does actually reinforce his argument - if many human societies across time and space have polyandry, then it’s actually more unlikely that the pair-bonding inhibition hypothesis is true.

Within the United States, it’s difficult to estimate the rate of lifelong pairbonding, though based on the following facts:

• 50% of marriages survive by 20 years (Copen, 2012). 

• 25% of 40 year old Americans have never been married (Fry, 2023)

• About 4% of Americans are widowed by 50 years of age (Carlson, 2020).

• Some people form lifelong non-marital relationships, though these are not that common, especially in the United States.

I would estimate that roughly ~30% of people form a lifelong pairbond that lasts until both partners die in their old age. Also, laser-focusing on base rates is not always informative, as these base rates can correlate substantially with other traits. For example, women who hold a bachelor’s degree have a 78% survival rate after 20 years, meaning that social status or (more likely) psychological characteristics influence the probability a given marriage will survive.

Regardless, as Alexander pointed out in the original blog post, there is no hard evidence for multiple sexual/romantic encounters resulting in decreased pair-bonding ability. I think it’s possible that within people who want to form a lifelong pairbond, unsuccessful attempts to make one would dissuade them from trying again, but people who have a large amount of long-term (e.g. 3-12 month) relationships that fail don’t have strong prospects of forming one anyway.

Given that the two most plausible causal explanations for promiscuous behaviour affecting relationship formation are either false or unfalsifiable, this raises questions about the causal nature of the relationship observed between an individual's number of sexual partners and their risk of divorce. Nevertheless, I think it is appropriate to highlight the research that supports a causal relationship.

One of these papers is a study conducted by Treas & Giesen (2000), who have evaluated whether the number of sexual partners an individual has prior to union affects the odds of infidelity independent of several other variables, such as educational attainment, race attitudes about infidelity, and sexual interest. Because infidelity is highly frowned upon in monogamous marriages and is a frequently cited cause of divorce, measuring it as an outcome variable will indirectly measure divorce as well. Among the three methods they used to measure infidelity, the number of sexual partners predicted an increase in the odds of infidelity (1.011x per partner) after controlling for various covariates in two out of the three ways they measure infidelity. Controlling for attitudes about infidelity, sexual interest in others, and relationship dissatisfaction barely changes the estimate - the beta was reduced from 0.14 to 0.11. 

Based on this table, an increase of 10 premarital sexual partners is associated with a multiplication in odds of being unfaithful by 1.11. By comparison, being Black predicts a multiplication in odds of being unfaithful by 2.44, and being male multiplies them by 1.35. Overall, it isn’t a very strong effect if you compare it to the other variables in the dataset.

Smith and Wolfinger (2021) have attempted to verify whether the correlation between multiple sexual partners prior to marriage and divorce persists after controlling for various covariates. These include sex, race, parental education, respondent education, premarital births, premarital cohabitation, age at first sex, sexual abuse as a child, religious identification, pledge to keep virginity, depressive symptoms, delinquent behaviour, relationship with parents, age at marriage, and family structure transition. He found that, regardless of the model used, premarital sex was a robust predictor of divorce (p < .001). The strength of the association is moderate - compared to those with no premarital partners, having 1-8 sexual partners was associated with a doubling in the odds of getting divorced, while having 9 or more partners predicted a tripling in odds of getting divorced.

Note the way the number of premarital partners is classified: 0 premarital partners, 1-8 premarital partners, or over 9 premarital partners. This is a rather convenient way of classifying premarital partners - remember that the rates of divorce were the highest for those with 2 or over 10 premarital partners. A more suitable approach for this analysis would involve treating the number of sexual partners as a continuous variable rather than a categorical one.

In addition, neither of these studies controls for a very relevant variable - personality. Sociosexuality is positively correlated with extraversion, disagreeableness, disorderliness, neuroticism, and openness (Schmitt & Shackelford, 2008; Rogowska et al., 2020). For divorce, extroversion, disorderliness, and neuroticism are also the most predictive personality traits (Boertien & Mortelmans, 2017). A small, but high quality study which uses peer-reported personality instead of self-reports finds that neuroticism and impulsivity (only within men) were the variables with the most consistent and positive links to divorce (Kelly & Conley, 1987). The data suggests that the personality traits associated with sociosexuality overlap with those linked to divorce. Therefore, it is advisable to consider these personality traits when conducting analyses.

Given that a lot of psychological science is of low quality, large datasets such as the UK Biobank would be useful to determine if these findings replicate. I investigated which variables were genetically correlated to your number of sexual partners, restricting my search to those with a p-value of under .00001 to protect against false positives. I have found that  your number of sexual partners is genetically correlated with the following traits:

• Belittlement by partner or ex-partner as an adult (r = 0.41)

• Physical violence by partner or ex-partner as an adult (r = 0.6)

• Risk taking (r = 0.59)

• Tobacco smoking (r = 0.51)

• Frequency of consuming six or more units of alcohol (r = 0.34)

• Feeling loved as a child (r = -0.43)

• Feelings of depression (r = 0.22)

• Loneliness/isolation (r = 0.26)

• Highly irritable/argumentative for two days (r = 0.25)

• Thinking life is not worth living (r = 0.25)

In some of these cases I could see there being a potential causal relationship - if you have sex with a lot of people, the chances that you face violence or belittlement from a partner increase. In the other cases, they corroborate the prior research which suggests that your body count correlates with neuroticism and risk taking behaviour.

Overall, the existing research suggests that premarital sex does not cause mental health issues, probably doesn’t inhibit pair-bonding, and that it is uncertain whether it causes marital dissolution or divorce. From a common sense perspective, the context in which somebody had sex with another person is probably much more relevant than the number of people they did it with. A 25 year old who had 8 prior relationships that all ended explosively is probably a bigger risk than somebody who had sex with 20 random people in college. 

I do think that if a person has multiple long term relationships that fail, they will be more jaded about their ability to form one, and that will affect their likelihood of forming one in the future. However, most of the evidence I have discussed in the article is more consistent with the confounding hypothesis, though I don’t think has been definitively proven.

As for why the relationship between your number of sexual partners and divorce is not linear, and peaks at 2 and 10 - I think it’s because those who marry their first partner probably have personality traits that lend themselves to having stable relationships, while those who married a 2nd or 3rd partner probably wanted to settle down early, but may have personal issues which makes it difficult for them to form stable romantic relationships. Beyond 2-4 sexual partners, those with more may not have been trying to optimize for a long-term romantic relationship in the first place, so their sexual history is less indicative of their personality. 

Disclaimer

I do not support promiscuity/the sexual revolution in general, and this post is meant to communicate that this “pair bonding” or “mental health” line of attack is not a fruitful, and the sexual revolution is best attacked based on its effect on the general population.

As for what I think the true effect of body count on mental health/relationship outcomes is, I do think that there is a small 0 → 1 effect for body count. People who have only ever dated their significant other may have a special bond with them which makes the relationship more likely to last. After that, romantic partners are seen as more serial or disposable, leading to a rational and utilitarian mindset that may not be optimal for growing long term romantic bonds. I must admit that there is no evidence to support my theory, though.

References

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Black, F. (2022, March 13). Let’s talk about casual sex, psychological well-being and marital quality. Nullsci’s Corner. https://blackfrancis.substack.com/p/lets-talk-about-casual-sex-psychological

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