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on the other hand

21 january 2018

Howard Kushner's On the Other Hand is a review of the history and current state of scientific knowledge about human handedness. This doesn't sound like thrilling reading, but it is. On the Other Hand is an incisive look at the cultural context for, and internal politics of, research on human subjects.

At first blush you wouldn't think there was much controversy possible in the study of handedness. I spend a lot of time reading about sabermetrics, for instance, the study of baseball statistics. In the folklore of baseball, there's a lot of gab about the flakiness of southpaws. But in sabermetrics, your batting side or throwing hand is just a variable. If a guy can't hit lefties, he's not a moral or mental failure. He's just a platoon player.

Wouldn't studies of people who write, eat, use scissors, masturbate, or wipe their behinds with a given hand be similar? But there, Kushner observes, is the difficulty. No human culture seems to be free from prejudices against people who prefer their left hands. Left-handedness is sinister, gauche, and otherwise taboo. The rhetoric of science insists that taboos should be vanquished in the quest for impartial knowledge. But the practice of science, especially when it comes to humans, can be surprisingly shackled to irrational beliefs.

Left-handedness, in the scientific literature, keeps getting associated with pathology, with "insult" to the developing brain, with stresses to the maternal womb (130-32). Often the assumption is that right-handedness is both normal and adaptive, and thus left-handedness must be a derangement of the natural state of affairs. Left-handedness gets further associated with femininity, criminality, savagery, madness, autism, and homosexuality. You might expect this from phrenological savants of the 19th century, but Kushner traces the persistence of such assumptions well into the 21st.

This all seems bizarre. Surely you're either left-handed or right-handed, Sandy Koufax or Don Drysdale; and surely by now they'd have found the gene that makes you so, like the genes for eye color and blood type. How hard can this stuff be? But handedness is, to date, intractable.

For one thing, which-handed you are is not cut-and-dried. To determine handedness, modern researchers use handedness inventories, where subjects self-report their preferred hand for various tasks. This turns out to be better than observing subjects, because the observing researcher may be biased. But of course so may the reporting subject. I scored in the fourth decile for right-handedness, for instance, but I did the inventory while I was reading On the Other Hand, and who knows where I would have scored if I'd answered the questions out of the blue. That there are deciles to fall into suggests that handedness is a continuum, not an either-or. In baseball, you can't throw a little bit right-handed; you have to make up your mind what kind of glove to wear (Greg Harris and Pat Venditte excepted). In everyday life, though, hand preference is more of a mix and match.

Individual handedness is clearly in part culturally determined. Writing comes to the modern mind as the quintessential locus of handedness, but most humans in world history have been illiterate, and many still are today. Writing must be taught; no-one does it spontaneously. In many cultures – in the US, historically – kids who showed signs of writing left-handed were trained, even beaten, into right-handedness. There appear to be almost no left-handers in present-day China, for instance. If one's writing hand reflected something innate and heritable, this would suggest interesting genetic differences between Chinese people and westerners; but it's simpler to infer that Chinese schools simply don't tolerate left-handers.

Eating is likewise a matter of table manners. Many lefties have to use scissors right-handed because their scissors don't work the other way. I mentioned masturbation and personal hygiene above, but Kushner invokes the latter only in passing (57) and the former not at all. Of course, taboos on eating with the same hand that you touch yourself intimately with might also interfere with "natural" preferences. Genital or anal touching seems not to be on the inventories because to ask about such things is impolite, even if they are more primal indicators than striking a match or moving a computer mouse. (Who uses mouses anymore anyway?)

Figuring out who's "really" right- or left-handed, and even what it really means to be one or the other, is a parlous enterprise. The next step, determining the origins of handedness (either in evolutionary or developmental terms – phylogeny or ontogeny) would seem to be doomed from the start. But that hasn't stopped researchers from opining and constructing models.

In evolutionary terms, handedness may be adaptive (there's some reason why having a dominant hand is advantageous, and why right-handers, the majority, are especially advantaged) or exaptive (something about the human brain tilts one way or another, who knows why originally, and we end up better at stuff with one hand than the other as an incidental result). In developmental terms, an individual's handedness may be genetic, environmentally fixed, or culturally dictated. (Or some mix of the three in varying proportions, though the blurrier that theory gets, the unsexier it becomes in terms of attracting headlines or grant funding.)

Data intriguingly show that you might be a little more likely to be left-handed if you have left-handed parents, so initially it was thought that handedness might be a Mendelian trait (strictly either-or, and heritable, like blood type). But the patterns aren't clear enough. Ingenious researchers (Kushner cites Marian Annett in particular) have theorized about complexes of interacting genes that might explain the observed distributions. But like so much theory about genetic traits, their ideas are indirect. You can posit a gene that contributes to handedness, but you can't immediately go to the human genome map and point to its location, even in the year 2018.

Kushner points out that both environmental and genetic explanations tend to assume that the natural, healthy state of the brain is for language and dexterity to be located in the left brain (and thus the right hand) – even though lots of perfectly normal people differ. In the 21st century, researchers continue to associate left-handedness with abnormality, including learning disorders, autism, and schizophrenia – though also at times with dreamy aesthetic natures and intense creativity, great wits being to madness near allied. Kushner, reviewing this literature, pretty much demolishes it. He may have axes to grind that he's not revealing, but his critique is convincing to a lay reader. Kushner emphasizes that straightforward correlations between strong left-handedness and any "abnormal" conditions are lacking. So researchers have to look at "non-right-handedness" – in other words, people who, like me, aren't at the far end of one of those handedness inventories, and thus presumably a bit messed up, brainwise. In such studies (mostly meta-analyses of other studies, at some distance from the generation of the data and possibly preferred because they don't need new clearance from human-subjects review boards), some correlations begin to show up. But these correlations are vague, and say little about the possible mechanisms at work. And Kushner notes tellingly that studies that find no correlations don't get published, or perhaps even written up.

In evolutionary terms, the literature gets even wackier. Kushner refers to something called the "fighting hypothesis" (113-122). Why are most people right-handed? Well, back in the day they would do battle quite a bit, with swords and shields and such. Now, you want to hold your shield in your left hand to cover your heart. This means slashing your sword around with your right. Fair enough. Note that we're talking men here (well, mostly), but fair enough.

But why didn't left-handers all die out, stabbed through the heart? The fighting hypothesis suggests that if everybody's fighting righty, you get a platoon advantage by fighting lefty. But it's not that great an advantage, and there's still the heart-stabbing thing, so via game theory we arrive at the current, supposedly optimized, R/L ratio. (Assuming that the stabbers out-reproduce the stabbees and the non-fighters; again, fair enough. Chicks dig stabbers, I suppose.)

This is what they call a "just-so story," but oddly, Kushner finds it one of the more plausible evolutionary scenarios concocted. (Despite the objection that if somebody's coming at you with a sword and shield, you can just throw something at them, with either hand.) Kushner doesn't deride the fighting hypothesis, because historically speaking, the ideas of a character like Cesare Lombroso, the late-19th-century criminologist, are infinitely worse. Lombroso believed in a world where savages did their brutish thing left-handedly or indiscriminately. Society reached a stage that could produce a Lombroso by writing and painting masterpieces with their right hands. Criminals, thought Lombroso, were atavistic savages.

One problem with this theory was that others connected left-handedness with both savagery and Jewishness; and Lombroso was Jewish. So he exempted Jews from the sinister cluster of associations as a special case. The younger scholar Robert Hertz, an anthropologist (also Jewish) killed in the first world war, went further to argue for lefty liberation – but in many ways, says Kushner, Hertz's combination of common sense and idealism has never won out against anti-left prejudices in the academy and elsewhere.

There's much else to admire, and learn from, in Kusher's study. But I want to close with an application that he does not make. Every few years, the study of race and intelligence raises its head again, and people claim to have found connections between ancestry (sorted by skin color) and smarts. Nobody seems to be able to observe these connections up close. Few white people will admit that they find black people to be stupid, less because of the PC police, I think, than because they never actually observe such racialized stupidity. Race/intelligence "science" must depend on subtle, unobservable connections that somehow still justify prejudice.

Think about that – about the myriad problems in defining and measuring intelligence, in tracing its origins to genes, environment, culture, in proposing evolutionary or developmental models to account for intelligence. And then think about the impenetrable difficulties of studying a simple matter like handedness, which you can clearly identify in others by watching them comb their hair or pitch a few innings of the World Series. And then be very, very skeptical when somebody claims that "science has shown" that white people have the upper hand when it comes to brains.

Kushner, Howard I. On the Other Hand: Left hand, right brain, mental disorder, and history. Baltimore: Johns Hopkins University Press, 2017. RC 386.6.N48