JY’s Five Finger Discount

Sufficient Heritable Variation?

Sufficient Heritable Variation?

In his recent blog post, evolutionary biologist and sleeping-with-mean-people advocate Jeremy Yoder tries his best to win an argument by shoplifting the conclusion rather than paying for it with good points. If you’re just tuning in, our debate was initiated when he bombed my Don’t Sleep With Mean People campaign Pearl Harbour style, prompting me to respond with a challenge: since Yoder claims he is keen to support a project of mine that teaches people about evolution, he should concede that this project is a worthy one and pay up. One thing I didn’t expect to have to do is teach an evolutionary biologist about evolution, but since this one keeps digging himself deeper, here goes.

In his original post, Yoder argued that the DSWMP slogan would never work because it assumes “the major component of variation in meanness is explained by genetics” and because the meanest people he could imagine – Rush Limbaugh, Simon Cowell, and Anne Coulter – would always be rationalized as charming and kind by their lovers. Although I deliberately left the definition of “mean” open-ended (ie “don’t sleep with homophobes” is a fair interpretation), I had less innocuous forms of meanness than social conservatism in mind, things like violence, aggression, cruelty, coercion, etc, the kinds of behaviours that incur felony charges and are overwhelmingly a male-perpetrated phenomenon. In his new post, Yoder’s argument is not that male violence isn’t an adaptation; rather, he argues that our violent tendencies have been so completely drilled into us by natural selection that they show insufficient genetic variation for selection to act on:

It may well be that there is something programmed into the development of human males that makes us, as a group, more likely to be violent once we’ve reached maturity—and, certainly, the development of boys into men is controlled by our genes. But natural selection (or artificial selection promoted by a nerd-rapper) needs genetic variation in order to operate. The fact that every male becomes more violent after puberty doesn’t tell us anything at all about whether individual differences in the magnitude of that change—differences that can be dramatic, both across and within cultural groups—are due to individual genetic differences. And if you don’t know that, you really can’t claim that you could select for reduced masculine meanness.

He’s right that a complete lack of individual genetic differences in proneness-to-violence would be a death-blow for my campaign, but luckily for me and all the other peaceniks who support the DSWMP credo, Yoder simply didn’t bother to look up any of the evidence.

A brief search of “genetics” “heritability” “aggression” and “violence” turns up compelling studies from Applied Genetics and Neuroscience, but the best evidence comes from Behavioural Genetics. Behavioural geneticists have devised excellent methods for estimating the amount of heritable variation in personality and behaviour, and proneness to violence is definitely part of their repertoire. They measure heritability by looking at the differences between pairs of fraternal and identical twins raised together and raised apart, and by looking at the similarities and differences between adopted siblings raised in the same home, thus controlling for environmental vs genetic influences. The New York Times summarizes one research finding (Kevin Beaver’s) like so:

He has tried to measure which circumstances — having delinquent friends, living in a disadvantaged neighborhood — influence whether a predisposition to violence surfaces. After studying twins and siblings, he came up with an astonishing result: In boys not exposed to the risk factors, genetics played no role in any of their violent behavior. The positive environment had prevented the genetic switches… that affect aggression from being turned on. In boys with eight or more risk factors, however, genes explained 80 percent of their violence.

When Yoder falsely criticized me for assuming that “the major component of variation in meanness is explained by genetics” I responded that he was overstating the case: all we need is for the variation to have some genetic basis, even a minor component, and DSWMP would have an effect. Ironically, the evidence suggests that in high risk populations the difference between a violent thug and a good citizen shows 80% heritability! I’m also willing to bet that among the “risk factors” being measured, they didn’t include the presence or absence of conscientious young women promoting the sexual attractiveness of peaceful conflict resolution. “Don’t Sleep With Mean People” is another way of saying: if women take a stand and proclaim that they won’t be turned on by aggression, that could prevent the genetic switches behind aggression from being turned on.

Yoder’s recent argument also contains an interesting analogy that I’d like to expand on. He likens “being a violent male” to “having five fingers on each hand,” with the implication being that it might in fact be entirely environmental conditions that cause any variation from the norm:

Consider another trait that is invariant across human populations: almost everyone on the planet has five fingers on each hand. Five-fingered hands absolutely have a genetic basis… But knowing this doesn’t tell us, when we see a man with only four fingers, that there’s a genetic basis to the variation he represents. Environmental conditions can have profound effects on human skeletal morphology.

As a thought experiment, imagine a hypothetical population of humans where the culturally-favoured method of male-on-male competition is knife fights. Imagine also that knife fights in that population are pretty much the only way a man ever loses fingers, and only the winners are missing fingers, because the losers are all dead (good fighters enjoy a straightforward fitness advantage). Finally, imagine that not all men get into knife fights with equal frequency; some prefer to compete instead with poems or music or by arguing publicly over scientific nuances, and some prefer a combination of strategies. If the tendency to get into knife fights were linked to some stable, heritable personality trait, for instance (dis)agreeableness – and if the heritable variation in that trait were estimated at, say, around 41% or 42% – then having four fingers or less would show significant heritable variation!

Of course, all babies without defects would still be born with five fingers, but the odds of losing one or more fingers after puberty would be strongly influenced by genes. Twin studies would reveal that identical twins were more likely to end up with correlated finger numbers than fraternal twins, and adopted siblings would more closely resemble their biological parents than their adopted parents in number of fingers lost over a lifetime. This is just to point out that Yoder may have his thumb unfairly pressed on the scale in favour of “environmental” factors, which might in some cases be a part of our extended phenotype.

Now imagine some enterprising troubadour, concerned both for the welfare of society (such a pointless waste of fingers!) and for his own welfare as a better wordsmith than a knife fighter, were to write a semi-serious but whimsical song encouraging women not to sleep with men who are missing fingers, which could serve as a proxy for the genes behind the fighting. The women might still be attracted to knife fighters, but also to troubadours and scientists and other types as well, and they might be sick of all the bloodshed. If the song quickly caught on and the women (and gay men) could be heard to sing “He’s no good for kissing, his fingers are missing” on every street corner, knife fighting might disappear from the population, even if the genetic variation remained. Changing the cultural triggers would have the same phenotypic effect as changing the genes. Those low-agreeableness high-aggression low-compassion genes might persist in the gene pool for some time, grudgingly muted by the new culturally-imposed standard of good behaviour, but without their fitness advantage they would eventually be lost to drift.

In the same way, my DSWMP campaign targets the intersection of culture and genes. It also assumes that the effects of genes on human behaviour, and the effects of sexual selection (intentional or otherwise) on gene frequency are probabilistic rather than one-to-one deterministic. If the campaign decreases the likelihood of genes “for” violence (ie genes that increase the probability of violence in certain contexts) being either expressed or passed on at all, I will be satisfied, and if it teaches a few people about evolution in the process, even better.

This entry was posted in Blog. Bookmark the permalink.

5 Responses to JY’s Five Finger Discount

  1. sarah h says:

    You realize that by focusing on women’s choices, this whole concept is a little sexist, right? That you – a man – are saying women need to be educated – by you – about who they should sleep with? It’s a fine concept as a joke (with responsibility equally distributed to both sexes), but by maintaining you’re serious and admittedly focusing on females, it’s kinds of offensive. It implies women are incapable of making their own choices, that youknow better than us and the burden to rid the world of ‘meanness’ lies solely on one gender. That women can’t sleep with who we’re attracted to because we might get pregnant but aggressive men hold no responsibility for spreading their own genes? I find your assertion that women should ‘take a stand and proclaim they won’t be turned on by aggression’ particularly painful. Just my 2 cents…

    • Baba Brinkman says:

      Thanks for your comment Sarah. I tried to carefully word that painful assertion not as a moral “should” but as a predictive “if… then”. I’m not telling women what they should do, I’m pointing out: if women choose differently, men will probably behave differently (a la Lysistrata). This prediction is based both on common sense and on evolutionary theory, as I explain in the project FAQs.

      I’m not sure why you say my campaign implies a lack of female choice – it’s really the opposite. I’m assuming women can and do control the majority of all sexual and reproductive decisions (their bodies after all). I’m also assuming men commit the majority of aggressive “mean” actions, often for the purpose of outcompeting other men for status, and status is clearly a turn-on for women (homeless guys don’t get laid). But there are many paths to status, some meaner than others. If these imbalances exist and arise from a deep part of our nature, it suggests an obvious path to change behaviour by changing the incentives.

      If you’re overwhelmingly attracted only to mean guys then of course follow your heart, but if you’re on the fence between two guys and one of them is a sweetheart while the other is an asshole, going with the sweetheart is not only a good move for you and your family, it’s also good for society and the species. That’s my claim, anyway.

      • sarah h says:

        hi again – thanks for responding to my comment above. unfortunately, i just really think the whole DSWMP thing is based on a lot of poorly supported and slightly sexist assumptions and the overall message is condescending to women. how many women do you know that are actively trying to have children with rapists and murderers? and of those (if they exist), how many would change their behavior if you told them to not do that because it is “a good move for you and your family…society and the species”? it’s just silly and i’m pretty sure that whether or not evolutionary theory is on your side, the numbers (like how strong selection would have to be to have any influence at all in the human population) are not.

    • Bryan says:

      I think that the campaign could certainly apply equally to men. If men stopped sleeping with mean women, I think the same arguments regarding genetic effects apply. And, as Baba mentioned in a previous post, the cultural effects would persist regardless of sexual orientation (e.g., men shouldn’t sleep with mean men, either!).

      It seems like Sarah sees the whole project as a bit paternalistic. But are Baba’s arguments really asking you to believe him because he’s male, and knows better? I don’t personally think so. While you may disagree with his reasons and conclusions, I encourage you not to dismiss his thoughts due to his gender.

      Of course aggressive men need to take responsibility for their own genetic propagation. As with any consensual sexual act, both parties bear responsibility. That means that either party can take a stand – and Baba’s focus here is on the party that seems more likely to be swayed (is it easier to convince mean people, or those they sleep with)? Perhaps this is a false assumption, and people who sleep with mean people are just as intractable. This seems to be Sarah’s point below, and a decent one.

      Lastly – appreciate your collected response here Baba. Way to stay classy.

      -B

  2. Pingback: Who are the people in your neighborhood, Baba Brinkman? « Nothing in Biology Makes Sense!

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>