The modified fighting hypothesis of handedness: Evidence from sharp force injuries and further considerations

The modified fighting hypothesis (MFH) proposes that most humans are right-handed because it conveyed an advantage during intraspecific fights with sharp weapons, due to the leftward location of the heart and aorta. An examination of the literature on sharp force injury showed that the thoracic region is penetrated more than any other region, and the left thorax is penetrated approximately 2.4 times more often than the right thorax. Handedness influenced the side of the thorax targeted, with most right-handers penetrating the left thorax in front of their right hand. As two thirds of the heart is in the left thorax, right-handers appear more likely to injure the heart and other vital structures, increasing their lethality when using a sharp weapon. This difference in lethality may have resulted in a survival advantage for right-handers. We discuss the possibility that increased use of sharp weapons in hominins caused evolutionary changes in anatomical traits, reducing sexual dimorphism and increasing population-level right lateralization. Similarities in lateralized fighting in humans and non-human species are considered and related to the MFH.