You cannot be serious - are left-handed people nature's way of starting a fight?

Alexander the Great was one, as was Billy the Kid and John McEnroe. Now scientists believe they can explain why some people are left-handed, and it's all to do with coming out on top in a fight.

Alexander the Great was one, as was Billy the Kid and John McEnroe. Now scientists believe they can explain why some people are left-handed, and it's all to do with coming out on top in a fight.

About 10 per cent of Britons habitually use their left hand rather than their right and for years biologists have been mystified as to why such a significant minority of people should be born left-handed.

It is known that left-handers tend to suffer more health problems and are at greater risk of serious accidents compared to right-handers. So, all other things being equal, the left-handed trait, which is largely genetic, should have died out long ago in prehistory.

There must, therefore, be some hidden advantage to being left-handed that counteracts the risks, but the problem for biologists was trying to work out what this advantage was. One idea is that, in the days when arguments were resolved by hand-to-hand combat, being left-handed gave people the benefit of surprise against right-handers. This advantage, however, would only have persisted if left-handers remained in the minority, otherwise right-handers would soon get accustomed to fighting with left-handed opponents.

Now two researchers from the University of Montpellier have found evidence to support this controversial idea. They believe that the more violence there is in a pre-industrial society, the greater the advantage of being left-handed.

Charlotte Faurie and Michel Raymond compared homicide rates, which includes murders and executions, in eight native societies around the world, from the Inuit of the Arctic to the Yanamamo indians of the Amazon. They found that as this measure of violent aggression increased in each society, so did the proportion of men who are left-handed.

Dr Faurie said: "We have found a direct correlation between the level of violence in a given society and the proportion of left-handers. This indicates that fighting can be an important selection pressure in the evolution of left-handedness."

They admit that a homicide rate that includes executions and gang murders is probably not an accurate measure of one-to-one fights in society, but it was the best measure available. "This result strongly supports the fighting hypothesis. More generally, it points to the importance of violence in understanding the evolution of handedness in humans," she said. Left-handedness has existed in human societies since the upper Palaeolithic, or early Stone Age, and in every society studied, it is right-handers who have been in the majority.

It is also well established that left-handers often have an edge in sports such as tennis, cricket, boxing or baseball, where there are dual confrontations between opposing competitors. Other sports, such as gymnastics, show no such bias.

Dr Faurie and Dr Raymond believe confrontational sports are similar to violent, one-on-one combat. "Interactive sports in Western societies are special cases of fights, with strict rules, including a particular prohibition of killing or intentionally wounding the opponent," they write in the journal Proceedings of the Royal Society B.

If left-handers in combat sports have an advantage when they are in the minority, then the same could also be true in fights and battles, they argue. "If this is true, then the advantage of being left-handed should be greater in a more violent context, which should result in a higher frequency of left-handers," they add.

This is just what the two researchers found when investigating homicide rates in the eight native societies they studied. They found the lowest murder rates and left-handedness in the Dioula tribe of Burkina, and the highest in the Yanamamo and the Jimi valley people of Papua New Guinea.

Dr Faurie said that the left-handed advantage would have only existed for men, who carry out most of the violent acts in any society. But the trait would still persist in women because it tends to be inherited through the maternal line. Professor Chris McManus of University College London, who has carried out an extensive investigation of left- and right- handedness, said that although the theory of Dr Faurie and Dr Raymond was plausible, there are problems in interpreting the data in they way they have. "The sample sizes were small and the methods they used were not as reliable as they could have been. I'm far from convinced," he said.

There must have been an advantage for a minority of people to be born left-handed, but trying to find out what this advantage was - or still is - remains unclear, he said. "The theory I've put forward is that despite the drawbacks of being left-handed, there are advantages in terms of creativity and other positive aspects," said the professor. "And society needed a subgroup who were different."

LEFT-HANDED LEADERS AND CRIMINALS

Alexander the Great

One of the most successful military commanders of the ancient world, he was King of Macedon from 336BC to his death in 323BC. His empire stretched from Greece to northern India.

Napoleon Bonaparte

The French Revolution general and ruler of France from 1799 was 28 when he had established himself as the greatest French general of all time.

Billy the Kid

According to legend, Billy the Kid killed 21 men, one for each year of his life - butthe actual figure is probably nine. The killer, born in 1860, was gunned down in the Chihuahuan desert by the New Mexico sheriff.

Jack the Ripper

His murders in east London in late 1888 have never been solved. Post-mortem evidence suggested that the Ripper was left-handed.