![]() Several hypotheses have been proposed to explain this extreme preference, including the use of tools, the larger size of the human brain, and the fact that humans live primarily on the ground. While it is known that handedness is caused by certain brain regions that are specialized in one of the two hemispheres, it is not clear how this evolved or why right-handedness dominates. Editor's evaluationĪbout 90% of humans are right-handed. Finally, our data show that human lateralization patterns do not align with trends found among other anthropoids, suggesting that unique selective pressures gave rise to the unusual hand preferences of our species. Furthermore, they point to a potential adaptive benefit of disparate lateralization strength in primates, a measure of hand preference that has often been overlooked in the past. These results challenge popular ideas on primate handedness evolution, including the postural origins hypothesis. In particular, terrestrial primates tend to display weaker hand preferences than arboreal species. In contrast, we recovered highly variable patterns of hand preference strength, which show signatures of both ecology and phylogeny. Species-level direction of manual lateralization was largely uniform among non-human primates and did not strongly correlate with any of the selected biological predictors, nor with phylogeny. We confirm that human right-handedness represents an unparalleled extreme among anthropoids and found taxa displaying population-level handedness to be rare. Based on that, we employ quantitative phylogenetic methods to test prevalent hypotheses on the roles of ecology, brain size, and tool use in primate handedness evolution. By combining original data with published literature reports, we assembled data on hand preferences for standardized object manipulation in 1786 individuals from 38 species of anthropoid primates, including monkeys, apes, and humans. Manual lateralization patterns in non-human primates have the potential to elucidate evolutionary determinants of human handedness, but restricted species samples and inconsistent methodologies have so far limited comparative phylogenetic studies. Modern Language Association, 8th ed., 2016.įor more info, see the MLA citation guide.The evolution of human right-handedness has been intensively debated for decades. Last modified September 14, 2020.įor more info, see the Chicago Manual citation guide. "Thumbs Up." ASU - Ask An Anthropologist. Retrieved June 02, 2023, from Īmerican Psychological Association, 6th ed., 2nd printing, 2009.įor more info, see the APA citation guide. Publisher: Arizona State University Institute of Human Origins Ask An AnthropologistĪPA Style Amy Peterson.Humans have a thumb on our hands, but we no longer have an opposable big toe. Colobus monkeys have greatly reduced the thumbs on their hands, because these monkeys no longer needed an opposable digit for how they move. For example, like most primates, chimps retained their “thumbs” on both their hands and feet. The opposable digit has evolved differently for different species. This trait became beneficial to survival and was passed to all the descendants of that ancestor species. Many millions of years ago, the ancestor to all living primates developed an opposable digit on its hands and feet, which allowed it to cling to branches in the trees where it lived. But they don’t have a brain like ours, so they can’t plan out making complex tools, and they don’t improve on the design of their tools over time.Īll living things have evolved through time in response to their environment. ![]() Their hands allow them to use some simple tools, like using a stick to get ants out of anthills. Our closest living relatives, chimpanzees, have hands that are similar to ours. Now, remove the straw and try to place the cap onto the bottle. Try to do some simple things, like picking up the straw. Have someone help you apply the tape to your hands so you cannot bend or move your thumbs. Even a simple task like placing a straw in a bottle becomes difficult! Why do you think human hands are shaped the way that they are? What you will need When you tape down your thumb, you’ll get a sense of how hard it would be to do many things if our hands were shaped differently. Our opposable thumbs let us grasp and manipulate objects. This experiment will demonstrate the importance of opposable thumbs.
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