Thursday, December 16, 2004

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Apparently my forefathers could kick some ass

The Economist has a story about why anyone (such as myself) is still left-handed. From an evolutionary perspective this is a puzzle, since "on average, left-handers are smaller and lighter than right-handers. That should put them at an evolutionary disadvantage." However, left-handers ostensibly have a distinct advantage in fighting: "most right-handed people have little experience of fighting left-handers, but not vice versa."

These stylized facts led Charlotte Faurie and Michel Raymond, of the University of Montpellier II (it's in France), to propose the following conjecture: "the advantage of being left-handed should be greater in a more violent context, which should result in a higher frequency of left-handers."

The Economist summarizes their findings:

Fighting in modern societies often involves the use of technology, notably firearms, that is unlikely to give any advantage to left-handers. So Dr Faurie and Dr Raymond decided to confine their investigation to the proportion of left-handers and the level of violence (by number of homicides) in traditional societies.

By trawling the literature, checking with police departments, and even going out into the field and asking people, the two researchers found that the proportion of left-handers in a traditional society is, indeed, correlated with its homicide rate. One of the highest proportions of left-handers, for example, was found among the Yanomamo of South America. Raiding and warfare are central to Yanomamo culture. The murder rate is 4 per 1,000 inhabitants per year (compared with, for example, 0.068 in New York). And, according to Dr Faurie and Dr Raymond, 22.6% of Yanomamo are left-handed. In contrast, Dioula-speaking people of Burkina Faso in West Africa are virtual pacifists. There are only 0.013 murders per 1,000 inhabitants among them and only 3.4% of the population is left-handed.

While there is no suggestion that left-handed people are more violent than the right-handed, it looks as though they are more successfully violent.

Here's a link to the academic paper.

posted by Dan on 12.16.04 at 12:00 PM


I always knew I was meant to be a slayer :)

The problem for me is that being an intellectual leftie in academics is a great advantage while being a physical leftie does not help at all. Maybe if we were to bring back the sword as dispute resolver at department meetings :P

posted by: dundare on 12.16.04 at 12:00 PM [permalink]

Although you should know that modern weapon design tends to standardized to right-handed user. English military still have NOT fix their SA-80 assault rifle to not poke left handed user's eye out (the ejected cartridge path for left handed user goes near the head).

posted by: BigFire on 12.16.04 at 12:00 PM [permalink]

Assuming we don't want a more violent society, the best thing left-handers can do to assure their survival is to promote baseball. Being a left-handed pitcher of even halfway decent quality assures you of a long-lasting major league career as a bullpen specialist, or as we stats geeks call them, LOOGYs (Left-handed One Out GuYs).

posted by: Devin McCullen on 12.16.04 at 12:00 PM [permalink]

Then why are you smiling?

I'm not left handed either.

posted by: Ugh on 12.16.04 at 12:00 PM [permalink]

Hmmm... more French anthropology using Yanomami case studies. Didn't the Chagnon scandal teach them anything? After reading Patrick Tierney's "Darkness in El Dorado," I'm inclined towards serious suspicion of the data on this supposedly warmongering people. Yanomami society has been so screwed up meddlesome anthropologists of the 'Gallic school' that the group has been declared off-limits by a lot of American anthropologists.

posted by: aaron on 12.16.04 at 12:00 PM [permalink]

How sinister.

posted by: Independent George on 12.16.04 at 12:00 PM [permalink]

Is left-handedness a genetically passed quality, or is it a randomly occuring quality? For this argument to hold, it has to be a genetically passed quality.
If its a randomly occuring quality (say, hypothetically, 5% of the population is born lefthanded), then for violent societies to reflect lefthandedness, those societies have to be violent enough to kill off enough righthanded people to shift the relative densities of the two groups. So, for instance, if random 5% of the population is born lefthanded, then to make up 15% of the population, they would have to kill of 2/3 of the total (5% of 100 = 5 people: 5 people = 15% of 33 total, so the other 67 were killed). To avoid this, left-handedness has to be genetically passed: left handed people have to be more likely to have left handed parents. Is this the case?


posted by: Steve on 12.16.04 at 12:00 PM [permalink]

Maybe societies with lots of cranky left-handers tend towards conflict.

posted by: rilkefan on 12.16.04 at 12:00 PM [permalink]

Devin McCullen: Being a left-handed pitcher of even halfway decent quality assures you of a long-lasting major league career as a bullpen specialist, or as we stats geeks call them, LOOGYs (Left-handed One Out GuYs).

Well, stats geeks also know that using LOOGYs hurts your bullpen. And given Boston's success after listening to stat guru Bill James, LOOGYs may be on the way out.

One can hope, anyway. These guys just destroy the pace of a game.

posted by: fling93 on 12.16.04 at 12:00 PM [permalink]

What interests me is, if the research is true, what is the optimal percentage to which left-handers can grow in the population before they are common enough for their uncommonness to no longer be an advantage? And if there is such an optimal percentage - maybe something like the 22.6 of the Yanomamo - wouldn't you expect their numbers in all populations to be around that percentage. Of course, there would be levels below and above this optimal level at which the left-handers' advantage would be nullified - too far above it, they'd be too numerous to have an advantage; too far below it, they'd be too few to be a threat. It would be to the right-hander's benefit to take them towards one of these extremes, away from their optimal.

And you thought there was a war in Iraq?

posted by: amit on 12.16.04 at 12:00 PM [permalink]

Here's an interesting little stat, with too small a sample size to be scientifically useful, but strange nonetheless.

For some reason, left-handedness is grossly over represented in State Dept's Near Eastern Bureau. I've been assigned to embassies where left-handed officers represented over 70% of the officer population; in embassies where it was "only" 30%. I've never been in one that had as small a fraction as 10%.

The common assumption was (and I say this as a left-hander) that writing Arabic meant you wouldn't get ink on your sleeves (Arabic being written right-to-left).

I've noted, too, though not as thoroughly, that left-handedness seems over-represented in both Saudi Arabia and Bahrain, among the indigenous populations. One would think that the left-hand taboo of Asians societies would strongly militate against this, but one would be wrong.

posted by: John on 12.16.04 at 12:00 PM [permalink]

I have previously posted comments expressing skepticism regarding the radical nature of the State Department.

I now retract those statements.

posted by: Andrew Steele on 12.16.04 at 12:00 PM [permalink]

I don't know that the Red Sox bullpen usage was actually that different than any other teams, so I wouldn't assume anything's going to change quickly. And in any case, the platoon advantage is real and measurable, so there's still going to be a desire for left-handers. (One of the main complaints from Yankee fans is that they didn't have a left-hander in the pen to deal with David Ortiz. And that's a more realistic complaint than the "A-Rod's a wimp" critique.)

posted by: Devin McCullen on 12.16.04 at 12:00 PM [permalink]

And in any case, the platoon advantage is real and measurable, so there's still going to be a desire for left-handers.

Oh, lefties will always be valued. But if clubs ever get a clue, they'll learn not to waste a roster spot with a marginal lefty whose only role is as a LOOGY.

I didn't follow the Red Sox closely, so I don't know if they used a LOOGY or not. As I said, might just be wishful thinking. But success is always quickly copied. After all, OBP is starting to become the rage. Linear Weights may not be far behind. And then maybe someday they'll fix or ditch the worthless save state.

posted by: fling93 on 12.16.04 at 12:00 PM [permalink]

In non-violent but non-advanced societies, lefthandedness is a disadvantage - we still kill ourselves off in accidents at an accelerated rate, but not so much as to avoid reproducing. So, the IDEA that a less-violent tribe would have fewer than a a more violent tribe makes some sense. Someone cited the Saudis - the Bedouin are pretty warlike, as have been the Arabs as a class.

I suspect lefties are overrepresented at State as a whole. We seem to also be overrepresented in public service as a whole. Don't know why.

posted by: rvman on 12.16.04 at 12:00 PM [permalink]

Steve, re: inherited handedness, both my parents are left-handed. My brother is (sort of) left-handed. I am right-handed. No one can figure this out.

posted by: rachel on 12.16.04 at 12:00 PM [permalink]

So it's alright been brought up in this series of comments that handedness may not be genetic. In fact, it may even be partially genetic. That is, there may be a genetic predisposition to certain handednesses, but that does not gaurantee that that handedness will assert itself.

Now, assume handedness is genetic, as, apparently, _The Economist_ does. Also assume that there is a major advantage to be right-handed over being left-handed. It's not clear to me why this would be the case. That is, why was there ever a greater number of right-handed people than left-handed people? But let's say that there is some sort of right-handed advantage.

Then this analysis becomes a game theory problem. I'm actually surprised to see that _The Economist_ doesn't approach it this way. The game in particular that I'm referring to is known as "Hawk-Dove." John Maynard Smith was the first to apply game theory to evolution, and he borrowed all of his theory from economics. He's the one who outlined the "Hawk-Dove."

The Hawk-Dove game assumes that in a conflict between two Hawks, the Hawks have to fight, and thus they both incur some cost. The one who loses incurs a great cost, and the one who wins incurs some gain. A similar event occurs when two Doves meet. If a Hawk meets a Dove, the Hawk pays no cost. The Dove gives up, and clearly pays a cost, and the Hawk gets some gain.

The question behind the Hawk-Dove is WHY would there ever be any Doves?

Well, it turns out that if it just costs too much to spend all your life as a Hawk fighting other Hawks, you have to keep some Doves around.

And it turns out that the relationship between how much you gain from a Dove and how much you gain (net) from another Hawk relates to how many Doves end up being left in the population.

And this relates to one of the other comments here that didn't really carry through.

Eventually you'll have so few left-handed people that the right-handed people will suffer too much cost only encountering right-handed people for all their lives. Thus the lefties gain some ground, and everything comes back to an equilibrium WITH lefties. This is the EVOLUTIONARILY STABLE STRATEGY (ESS).

And keep in mind that this has NOTHING TO DO WITH FIGHTING. There may be some other advantage to being right-handed. If all the technology in the world is designed for righties, then righties have a huge advantage over lefties when making a living. Trouble is, they may not have enough of an advantage over the rest of the righties to completely obliterate the lefties.

But there are a LOT of assumptions that go into any of this analysis. MUCH of handedness is pure chance. In that case, there's no clear reason why lefties would ever go away.

posted by: Theo on 12.16.04 at 12:00 PM [permalink]

You guys ever seen Rocky?

posted by: Chad on 12.16.04 at 12:00 PM [permalink]

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