By Dr David Whitehouse
BBC News Online science editor
The fraction of left-handed people today is about the same as it was during the Ice Age, according to data from prehistoric handprints.
They were found in caves painted during the Upper Palaeolithic period, between 30,000 and 10,000 years ago.
Left-handedness may have conferred prehistoric man advantages, such as in combat, say the researchers.
The research is published in the February issue of the journal Biology Letters.
Evolutionary advantages
When Stone Age man produced their remarkable cave paintings they often left handprints on the walls produced by blowing pigments from one hand through a tube held by the other hand.
Charlotte Faurie and Michel Raymond at the University of Montpellier, France, deduced the prehistoric cave painters' handedness by spraying paint against cave walls to see which hand they pressed against the wall, and therefore did not use for drawing.
Looking at 507 handprints from 26 caves in France and Spain, they deduced that 23% of them were right-handed, which indicated that they were made by left-handers.
In the general population today about 12% are left-handed, though populations vary considerably, between 3 and 30%.
Because handedness has a genetic component the researchers wondered why the proportion of left-handers should have remained so constant over 30,000 years - the age of the oldest cave studied.
They suggest that because left-handedness is relatively rare it provides certain advantages over those who are right-handed, such as in solo and group fighting.
The researchers say their findings add to the evidence that the evolutionary forces that cause right- and left-handedness are independent of culture.
