November 13, 2010

Why does promiscuity rise when violence levels soar?

What started me on this path of looking at the rising or falling of crime rates as a driver of larger social and cultural changes was the connection between the plummeting violent and property crime rates since their 1992 peak and the falling levels of sexual wildness among high schoolers during that same period, as reported by the bi-annual Youth Risk Behavior Survey.

One question asks if you've ever had sex, another if you've ever had sex before 13. It is straightforward how these behaviors will respond to a rise or fall in the violence level: when violence soars, people expect a shorter lifespan and therefore get an earlier start on life's major milestones, whereas a fall in the crime rate will produce the opposite effect because people expect a longer lifespan and thus lower costs to delaying maturity.

Yet the YRBS not only shows that people start to mature later after the fall in the crime rate, but that they have become far less promiscuous (a question asks if you've had 4+ partners in your life). Although we lack good survey data from the period when the crime rate was rising (1959 to 1992), it is clear that people became more promiscuous compared to the previous era of falling crime (1934 to 1958). The sexual revolution was not the figment of everyone's imagination.

What's the logic behind promiscuity tracking the violence level? I'll focus on females since male promiscuity is not surprising. It isn't immediately obvious, unlike earlier maturation. There are at least two reasons why: to recruit more male protectors into her social circle, and to further diversify her offspring as a hedge against a suddenly greater variety of dangers.

1) When violence soars, females want more male allies and friends in order to be better protected against the world's dangers. I've detailed before how violent times cause girls to want to hang out more with boys, while safe times lead them to retreat into the domestic sphere, have a few female friends, and perhaps some gay male friends only.

Part of what keeps males in her close circle of allies is the possibility of a sexual encounter or longer relationship. Granted this isn't a certainty, but it isn't trivial, and even a small probability of sex times a large number of female friends yields an expected number of sexual encounters within one's social circle that is worth the cost of protecting your chick friends. Readers who grew up mostly during violent times will be familiar with this, but it's worth stating it explicitly for the benefit of Millennials, who only came of age during highly sex-segregated times and have never had very close boy-girl friendships in the first place, let alone one that could go a little farther than that.

This pattern shows up in other primates, such as chimpanzees, where the female mates with many males in order to make each of them think they stand a chance of being the father and thus invest in her offspring (or at least refrain from harming them). Human females aren't more promiscuous for exactly the same reasons, but it's pretty similar -- recruiting more males who will help her out in surviving and ensuring her offspring survive too, when the danger to herself and her children starts to shoot up.

2) When violence soars, people not only perceive a shorter expected lifespan, but also a greater variance or unpredictability in the sources that these dangers are coming from. Suppose that the only reason that her expected lifespan has shortened is that there's a ritual sacrifice that used to occur upon her 70th birthday, but now occurs on her 60th. That would only lead to the change in when she got started sexually; it would not make her more promiscuous.

However, suppose that the cause of her shorter lifespan is a general rise in violence. This looks like a breakdown in the order of things, and that there are all sorts of dangers that no one had even imagined before. I mean, we had always been worried about catching a deadly infectious disease and had taken precautions against that -- but now it turns out that there's a supernatural killer who can enter your dreams and murder you when you're asleep, and that Satanic cults have taken over day-care centers in order to abuse your children as part of their perverse rituals, and so on. Who saw that coming?

If there were only one source of danger, then the female could plan for this very well -- just mate with a single male whose genes will make her offspring most robust to that danger. For example, if the only source of danger were a beast that could bite people 6' or taller, but which couldn't stoop low enough to bite people 5'3 or shorter, then she should mate with a very short male. Then her kids would be short enough to avoid this only source of danger.

Not so when the sources of danger seem to explode in variety -- and that's only the ones that people have currently seen. Who even knows about the new dangers that we haven't uncovered yet! Now she has to hedge her bets on where the danger to her kids will come from, namely by mating with a variety of males in order to diversify the portfolio of her offspring. Perhaps she should mate with an average-height and skinny lead singer of a rock band -- and then again maybe she should mate with a tall and muscular athlete. Well, when the variety of dangers starts to explode, why not have kids by both, just to cover all bases?

This is somewhat like the Red Queen argument for the evolution of sexual reproduction. After all, reproducing sexually involves more partners (at least one) than asexually (zero). William Hamilton's idea was that the wide variety of pathogens that one's offspring will face selected for a mating system where the genetic combinations could be scrambled every generation, throwing the pathogens off our track for a little bit. Bobbi Low showed that where pathogen load is higher, human males are more likely to be polygynous, which diversifies offspring more than monogamy, and especially in a non-sororal way (that is, the wives are not sisters, which further diversifies his offspring). As with violence, the sources of danger from pathogens present an endless variety every generation as the germs mutate and give rise to new strains.

Those who have read this blog for awhile will have noticed a major shift in my judgment of promiscuity. Earlier I saw falling promiscuity levels as a good sign of where society is headed. But after stumbling onto this secret passageway of how the violence level affects so much else, I've changed my mind. It's not that promiscuity per se is a socially desirable thing; probably all else equal, a society with more monogamy is more pleasant to live in for the average person. But all else is not equal -- so much else is inextricably tied to promiscuity.

Trust levels are one -- you wouldn't be so promiscuous if you weren't fairly trusting of others, and when you trust no one you won't take on many partners. Girls seeking out close friendships with boys is a subset of this. Only during violent and promiscuous times do boys and girls form tight bonds. And it affects female psychology -- if she is to be more promiscuous in her behavior, she must be capable of falling head over heels more easily, which puts her in a more romantic and boy-crazy mindset. On planet Earth, the alternative to this is not cool-headed rationality, which will never be common among females, but the cold-hearted mercenary use of her sexuality a la the femme fatales of film noir or the butt-kicking babes of the '90s and 2000s.

A greater chance of being cheated on, or dumped before cheating begins, and the greater costs this implies for heartbreak and for monitoring your girlfriend -- that's just the price you have to pay in order to enjoy the larger benefits in a rising-crime world, part of which is that girls will be more sexually curious and solicitous, more eager to hang out with the boys, more boy-crazy psychologically, and overall just more fun to be around.


  1. We see many of the same patterns, but I don't interpret this web of connections as driven by violence so much as coterminous with it. Violence, creativity, promiscuity, etc (Young Male Traits) all stem from the same hormone mediated drive: mating effort. This is the relative effort invested into finding sex partners vis-à-vis securing a long-term partner (parenting effort).

    Lower social classes are genetically biased towards mating effort, and violence has declined over the long term thanks in no small part to progressive genetic changes (i.e. the rich outbreeding the poor by being able to support larger families).

    Shorter term cycles obviously aren't due to genetic changes, and may have obscure and variegated social and biological explanations (e.g. economic conditions, environmental estrogens), which probably also involves many feedback loops. But I think the behavioral patterns themselves are traits that are developmentally linked. There are more violent and less violent people, and less violent people are simply less promiscuous.

    This means Millennials, on average, are less creative, less promiscuous, less violent, less risk-taking, and are more achievement motivated and future oriented . Contrary to theories of rising narcissism, I would say this also means they are more altruistic.

    In other words more "Asian".

    I interpret these developments as positive.

  2. I well remember the pre-1992 high crime era. You may dismiss this as anecdotal, but certainly no one I knew went around worrying that his or her life would be cut short by violence. Outside of some of the very worst neighborhoods the risk of violent death was minimal.


  3. Peter, look it up in the GSS. Fear of walking around your neighborhood tracks the crime rate.

    Jason, in a math model we'd use something like differential equations where the variables can all influence each other. But when you look at the initial conditions, which one looks to change first?

    Looks like violence levels -- the crime wave of the 1960s was visible before the sexual revolution. Same with the flappers of the 1920s, which were evident noticeably after the 1900 surge in violence began.

    Otherwise you have to ask what suddenly causes people to switch to shorter-term mating strategies, which then drive the other changes. If it's the level of violence, it's straightforward how that would push mating strategies in the shorter-term direction.

  4. Although there's something to be said for the "all about mating effort" idea, in view of Barry Sinervo's work on the side-blotched lizard.

    There are three morphs whose prevalence cycles in a paper-rock-scissors way. Each morph has a distinct mating strategy and approach to violence.

    There it looks like their violence strategies are just serving whatever their mating strategy is -- ultra-violent to guard a polygynous harem, non-confrontational for the fly-by-night "sneaky fuckers," and teaming up against the sneakers for the monogamous good dad morphs.

    But the human case doesn't look like that, as though males were getting much more violent in order to protect their harems. Or maybe the West of the past 1000 years is a too-new environment, and the "all about mating effort" idea works better when we look at hunter-gatherers, pastoralists, and pre-state agriculturalists.

  5. Jason,

    Is promiscuity a young male trait? Seems females are almost always the limiting factor among humans. Latitudinally, evidence for Agnostic's hypothesis abounds--women are more promiscuous in high crime, urban areas than they are in the plusher burbs, and girls who come from more chaotic family situations are generally easier than girls who come from functioning households.

  6. "Looks like violence levels -- the crime wave of the 1960s was visible before the sexual revolution. "

    I agree that this would be an illuminating analysis, and it is not an analysis I have done.

    I would predict that A) Changes of violence over time are almost always due to changing cohorts of young, prime breeding age males (16-25), B) The sexual behaviors of these new cohorts tracks their violent behavior. Men who are violent will report earlier sex and more sex partners. More men who are violent, means more men who are promiscuous, C) the female cohort behavior always trends in the same direction as the male behavior.

    Early sexual behavior is probably the best indicator. Millineals and late Gen Xrs are more "promiscuous" (cycle through more sexual relationships) in their 20s than previous cohorts, but only because they delay marriage longer (a modern consequence of high future orientation). But they don't display earlier sexual behavior because they are not biologically developed for high mating effort.

    But the human case doesn't look like that, as though males were getting much more violent in order to protect their harems.

    I think my understanding of violence paradigm shifted when I read David Buss's The Murderer Next Door. Almost all male on male violence (the most common kind) is related to young men competing for women, or trying to "save face" in conflicts where women are observing, by refusing to back down.

    I started to read my local police blotter after reading this book, and indeed, almost all male violence is related to mate competition.

    I most easily interpret changes in male violence over time as changes in conflict intensity over women.

  7. A.E.,

    Is promiscuity a young male trait? Seems females are almost always the limiting factor among humans.

    Yes, this is the gender and age group that is most likely to desire and seek out short term mating opportunities. Females are a limiting factor, but male and female behavior patterns/mating strategies trend together across time and place.

    "Latitudinally, evidence for Agnostic's hypothesis abounds--women are more promiscuous in high crime, urban areas than they are in the plusher burbs, and girls who come from more chaotic family situations are generally easier than girls who come from functioning households"

    Remember, Agro and I are mostly seeing the same patterns, so these examples don't help resolve the causal issue, which is where we seem to differ.

    Taking your latter example, this is one reason I think the mating effort patterns are primarily genetic/biological (as opposed to adaptive/responsive).

    The classic Harpending/Draper paper about CADS/DADS saw early female sexual behavior as a consequence of father absence, but research since then seems to support the idea that the connection is due to inheritance: high mating effort fathers (who are more likely to abandon their families) are simply more likely to father high mating effort daughters (who are more likely to have sex and get knocked up as teens). The adoption literature, more broadly, disfavors the home environment as a strong environmental influence.

  8. Agnostic,

    What do you think of Harpending and Cochran's contention at

    "The Whitings discussed as one extreme those societies where men and women lived together, slept and ate together, seemed to like each other, and cooperated in households. The called these “intimate” societies and found that a reliable indicator was sleeping arrangements: in these societies men and women slept together, often with their children. In the perspective of evolution and reproductive strategies these are societies where males are putting reproductive effort into parental effort, that is to say they are “dad ” societies. While there may be organized external warfare there is usually not much local raiding and warfare.

    At the other extreme are societies like those of many gardening groups where males and females don’t like each other very much, where relations between the sexes are, in the Whitings’ terms, “aloof.” Here men may sleep and live in men’s houses rather than in their wives’ houses. The men’s houses usually have some sort of ritual significance such that women are prohibited from entering them. They are low-tech societies’ versions of fraternity houses. While women work hard in these societies, men typically spend a lot of time in subtle and not so subtle male competition like debating, fighting, and planning the next round of fighting with the neighbors."

    Do you think there's any interface between this and your model of decreases in promiscuity driving greater sex separation and "aloofness"?

  9. I would guess that monagamous cultures are more trusting than polygynous ones.

  10. I guess the best test of your theories would be to apply them to Mexico. You would have recent data from the last 15 years which should show huge support for correlations you claim to see.
    I don't know if anyone is really looking at that, and I don't know how good the underlying data would be, but it sure could be great a case study.

  11. This is why I make that assumption about trust.

  12. r-selected cultures - the correlation exists for sure - but you can go the other way as well - promiscuity increases violence. Unrestrained female desire and unrestrained male anger are linked.


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