The evolution and biological correlates of hand preferences in anthropoid primates

The evolution of human right-handedness has been intensively debated for
decades. Manual lateralization patterns in non-human primates have the
potential to elucidate evolutionary determinants of human handedness.
However, restricted species samples and inconsistent methodologies have so
far limited comparative phylogenetic studies. By combining original data
with published literature reports, we assembled data on hand preferences
for standardized object manipulation in 1,786 individuals from 38 species
of anthropoid primates, including monkeys, apes, and humans. 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. We confirm that human right-handedness represents an
unparalleled extreme among anthropoids and found taxa displaying
population-level handedness to be rare. 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. In contrast, we recovered highly variable patterns of hand
preference strength, which show signatures of both ecology and phylogeny.
In particular, terrestrial primates tend to display weaker hand
preferences than arboreal species. These results challenge popular ideas
on primate handedness evolution, especially the postural origins
hypothesis. 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. 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.