<scp>PriMath</scp> —The Role of Intrinsic Factors in Quantitative Cognitive Performance of Highly Social Primates

Mechanisms by which animals acquire, process, store, and use information from their environment (i.e., cognitive abilities), like other traits, evolve in response to selection pressures. Individuals with distinct intrinsic traits may benefit to varying degrees from different strategies when solving ecologically relevant cognitive tasks. This effect may be especially pronounced in social species, where group composition can shape the development of different cognitive strategies. In this study, we investigated the quantity discrimination abilities of two highly social New World primates using spontaneous choice tests. Our aim was to explore the effects of species-specific biology and intrinsic traits, such as sex and age, on cognitive performance. We tested 14 focal individuals using five quantity combinations with varying ratios (0.25, 0.5, 0.75): 1 vs. 2, 1 vs. 4, 3 vs. 4, 6 vs. 8, and 6 vs. 12. We found that performance was primarily driven by ratio-dependence rather than absolute differences between quantities. This, combined with the lack of significant differences in response time across quantity combinations, suggests that the Approximate Number System (ANS) is the primary cognitive mechanism underlying quantity discrimination in the studied species. Additionally, response time varied with intrinsic traits such as species, sex, and age; however, we did not detect differences in performance. Our results may reflect the unique social structure of these species, as well as differences in their biology, such as feeding behavior, providing valuable insights into the quantitative abilities of New World monkeys. These findings highlight the need for a deeper exploration of the evolutionary trade-offs and selective pressures shaping the complex interactions among behavior, intrinsic traits, and cognitive performance.