Southpaws have rarity value when it comes to fighting.
Left-handed people thrive best in the most murderous societies, according to a study of tribes across the world. The discovery may help to answer the riddle of why a minority of left-handers persist in human populations.
Being a southpaw is an advantage in a host of confrontational situations. Lefties are far more common at the top of sports such as boxing and fencing than in normal society. The benefit comes from the element of surprise: most opponents will be less used to facing a left-handed adversary.
But left-handedness comes at a cost. Developmental experts think that stress during development or birth may divert the nervous system from its default, right-handed path. And developmental stress is also linked to reduced lifespan, low birthweight and increased incidence of immune and nervous disorders, meaning that natural selection might be expected to weed out lefties altogether.
Weigh it up
So might this combination of cost and benefit be what keeps left-handedness at its constant yet low level in the population? Charlotte Faurie and Michel Raymond, of the University of Montpellier II in France, investigated by studying eight different traditional societies. They compared the frequencies of left-handers in the tribes with the murder rates in their societies.
Among the Jula (Dioula) people of Burkina Faso, the most peaceful tribe studied, where the murder rate is 1 in 100,000 annually, left-handers make up 3.4% of the population. But in the Yanomami tribe of Venezuela, where more than 5 in 1,000 meet a violent end each year, southpaws account for 22.6%. Faurie and Raymond report their findings in the_ Proceedings of the Royal Society_.
The numbers are fairly rough and ready, admits Faurie. Many of the data rely on interviews with elder tribespeople, who may not report sensitive events truthfully or may have trouble recalling them. What's more, they only take account of fights that went right to the death.
Nonetheless, the relationship between murder rate and handedness is very clear, she says, despite the study's inaccuracies. This shows that left-handers really do benefit from their surprising style in hand-to-hand fights.
The picture is more complex in Western societies, where left-handedness hovers around the 10% mark. Although hardly free from one-on-one violence, the advent of long-range weapons such as guns and bombs complicates the picture, Faurie says.
But the pattern seen in the tribes matches that seen in the ritualized confrontations of Western sport, Faurie says. And left-handers enjoy the greatest success in those sports that are fought at closest quarters.
"The frequency of left-handers is much higher in sports," she says. "And in boxing and fencing it's higher than in tennis, where you're further away from each other. It's not at all seen in solo sports such as gymnastics: here left-handers are in the same proportion as in the general population."
FaurieC. & Raymond M._Proc. R. Soc. Lond. B_, published online, doi:10.1098/rspb.2004.2926 (2004).