Lateralization in seven lemur species when presented with a novel cognitive task

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, but 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 1786 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, including 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.

Preliminary comparisons of learning across four lemur genera at the Duke Lemur Center

Lemurs have been relatively understudied in cognitive research despite representing an adaptive radiation and occupying a key phylogenetic position as the most basal extant primate lineage. Many of the existing studies have focused on only one lemur species. We aimed to take a comparative approach by examining learning abilities in 66 lemurs from four genera at the Duke Lemur Center in North Carolina. We used a novel two-action puzzle box to assess inter-species variation in learning speed, task proficiency, and social tolerance during trials. We found differences between genera in the percentage of individuals who had successes, individuals’ latency to touch the apparatus and the number of times an individual observed a group member’s success. Eulemur and Varecia had shorter latencies and were observed more by conspecifics compared to Propithecus and Lemur. Shorter latencies may indicate reduced fear or increased motivation, while higher observation rates suggest more leniency or tolerance around the puzzle boxes. These results may be due to species differences in dominance and rank hierarchies; Propithecus and Lemur are more despotic than Eulemur, where some species exhibit sex co-dominance, and Varecia, which live in groups with high fission-fusion dynamics. We also show that even within these overall relationships, the different genera varied substantially in the temporal trajectory of these learning variables through the study trials. Overall, this comparative study provides preliminary insights into the taxon-specific learning trajectories of lemurs and contributes to the growing body of literature examining lemur cognition.