They looked at homicide-rates and the frequency of left-handedness, and found they appeared to be linked.
But the Eipo had around three homicides per 1, 000 people and a left-handedness rate of 20%.
But that raises a further question: if left-handedness is beneficial, then why is it so rare?
One was a handedeness test (left-handedness is more common among autistic people), and the remaining two evaluated facial recognition and language.
The researchers say their findings add to the evidence that the evolutionary forces that cause right- and left-handedness are independent of culture.
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.
Supposedly resulting from abnormal antenatal exposure to hormones, this cluster includes maleness, homosexuality, left-handedness, poor visual-spatial skills, immune disorders, and perhaps also language-learning talent.
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It all seems to parallel ideas about left-handedness in human cultures.
That may sound surprising, but high levels of testosterone in the womb have been linked to several other brain-related phenomena, including left-handedness, dyslexia and female homosexuality.
Professor McManus said the more likely explanation for the persistence of left-handedness was the need for individuals with a range of qualities and skills within societies.
Most interesting, I learned that many science fiction readers are Rationals in the Keirsey Temperament Sorter, which tells me that geekdom is as innate as left-handedness.
The Dioula were found to have a homicide rate equivalent of one hundredth of a death per 1, 000 people per year, and a left-handedness rate of just 3%.
Chris McManus, a professor of psychology at University College London who has made a study of the pros and cons of left-handedness, said it was true that left-handers did have an advantage in a fight.
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.
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