Why lefties are rare?

Washington, Apr 30 - Ever wondered why there are very few lefties compared to the number of right-handed people? It may be due to the balance between cooperation and competition in human evolution, scientists say.

Left-handers, who represent only 10 per cent of the human population, have been viewed with suspicion and persecuted across history. The word ÒsinisterÓ even derives from left or left-hand.
To find out why they are a rarity, researchers from the Northwestern University looked at data from the sports world.

They developed a mathematical model that showed that the low percentage of lefties could be a result of the balance between cooperation and competition in human evolution, LiveScience reported.

Prof Daniel Abrams, who led the study, said: ÒThe more social the animal -- where cooperation is highly valued -- the more the general population will trend toward one side.Ó ÒThe most important factor for an efficient society is a high degree of cooperation. In humans, this has resulted in a right-handed majority.Ó According to the researchers, who detailed their work in the Journal of the Royal Society Interface, if societies were entirely cooperative everyone would be same-handed. But, if competition were more important, one could expect the population to be 50-50, Prof Abrams said.

The new model can predict accurately the percentage of left-handers in a grouphumans, parrots, baseball players, golfersbased on the degrees of cooperation and competition in the social interaction, he said.
The model helps to explain our right-handed world now and historically: the 90-10 right-handed to left-handed ratio has remained the same for more than 5,000 years.

It also explains the dominance of left-handed athletes in many sports where competition can drive the number of lefties up to a disproportionate level, the researchers said.

Cooperation favours same-handedness for sharing the same tools, for example. Physical competition, on the other hand, favours the unusual. In a fight, a left-hander would have the advantage in a right-handed world, the researchers said.

Prof Abrams and co-researcher Mark Panaggio turned to the world of sports for data to support their balance of cooperation and competition theory.

Their model accurately predicted the number of elite left-handed athletes in baseball, boxing, hockey, fencing, and table tennismore than 50 per cent among top baseball players and well above 10 per cent (the general population rate) for the other sports.

On the other hand, the number of successful left-handed PGA golfers is very low, only four per cent. The model also accurately predicted this.

ÒThe accuracy of our model's predictions when applied to sports data supports the idea that we are seeing the same effect in human society,Ó Prof Abrams said.

Handedness -- the preference for using one hand over the other -- is partially genetic and partially environmental, and identical twins who share the same genes don't always share the same handedness, the researchers said.