Handedness in a nonindustrial society challenges the fighting hypothesis as an evolutionary explanation for left-handedness

Handedness is a heritable trait, and left-handedness is related with increased fitness costs. Left-handedness persists, however, as a minority in every human population investigated. One explanation for this persistence has been put forward in the fighting hypothesis, which postulates that left-handers have a frequency-dependent benefit in fights. Support for this has been found in the finding that left-handedness is relatively frequent in populations with high homicide rates, according to estimates of left-handedness partly based on pictures and films made for a different purpose. We measured handedness based on hand preference in 10 ecologically relevant tasks in 621 subjects in the nonindustrial society of the Eipo (Papua, Indonesia) in which homicide rate was very high. This set of tests was validated in 198 Western students. Contrary to the prediction based on the fighting hypothesis, we did not find a high frequency of left-handedness or a difference between men (who participate in warfare) and women (who do not). These findings challenge the idea that fighting is the driving evolutionary force for the persistence of left-handedness in human populations. Furthermore, we found lower percentages of left- and mixed-handers compared to a Western population who executed the same tasks. Since left-handedness is associated with health problems, we suggest that in a society lacking Western health care, selection pressures against left-handedness may be more intense and therefore its frequency may be reduced.