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The field of primate cognition studies how primates, including humans, perceive, process, store, retrieve, and use information to guide decision making and other behavior. Much of this research is motivated by a desire to understand how these abilities evolved. Large and diverse samples from a wide range of species are vital to achieving this goal. In reality, however, primate cognition research suffers from small sample sizes and is often limited to a handful of species, which constrains the evolutionary inferences we can draw. We conducted a systematic review of primate cognition research published between 2014 and 2019 to quantify the extent of this problem. Across 574 studies, the median sample size was 7 individuals. Less than 15% of primate species were studied at all, and only 19% of studies included more than one species. Further, the species that were studied varied widely in how much research attention they received, partly because a small number of test sites contributed most of the studies. These results suggest that the generalizability of primate cognition studies may be severely limited. Publication bias, questionable research practices, and a lack of replication attempts may exacerbate these problems. We describe the ManyPrimates project as one approach to overcoming some of these issues by establishing an infrastructure for large-scale collaboration in primate cognition research. Building on similar initiatives in other areas of psychology, this approach has already yielded one of the largest and most diverse primate samples to date and enables us to ask many research questions that can only be addressed through collaboration.

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Short-term memory is implicated in a range of cognitive abilities and is critical for understanding primate cognitive evolution. To investigate the effects of phylogeny, ecology and sociality on short-term memory, we tested the largest and most diverse primate sample to date (421 non-human primates across 41 species) in an experimental delayed-response task. Our results confirm previous findings that longer delays decrease memory performance across species and taxa. Our analyses demonstrate a considerable contribution of phylogeny over ecological and social factors on the distribution of short-term memory performance in primates; closely related species had more similar short-term memory abilities. Overall, individuals in the branch of Hominoidea performed better compared to Cercopithecoidea, who in turn performed above Platyrrhini and Strepsirrhini. Interdependencies between phylogeny and socioecology of a given species presented an obstacle to disentangling the effects of each of these factors on the evolution of short-term memory capacity. However, this study offers an important step forward in understanding the interspecies and individual variation in short-term memory ability by providing the first phylogenetic reconstruction of this trait’s evolutionary history. The dataset constitutes a unique resource for studying the evolution of primate cognition and the role of short-term memory in other cognitive abilities.

Meerkats are group-living, insectivorous herpestids in which subordinate members provide extensive care for the dominant female's young. In contrast to some cooperative breeders, subordinate female meerkats are physiologically able to reproduce and occasionally do so successfully; their attempts are more frequently 'suppressed' via eviction or infanticide by the dominant female. Spontaneous abortion and neonatal loss occur with some regularity, further negatively impacting reproductive success. Here, we compared the reproductive outcomes and endocrine profiles, including of serum progesterone (P), serum estradiol (E), and fecal glucocorticoid metabolites (fGCm), of dominant and subordinate dams residing within their clans in the Kalahari Desert of South Africa. Our study spanned years of drought, which reduced insect abundance and represented a substantial environmental stressor. Meerkat pregnancies were identified at mid-term and culminated either in spontaneous abortions or full-term deliveries, after which pups were either lost prior to emergence from the natal den (usually within 2days of birth) or emerged at 2-3weeks. Neonatal loss exceeded fetal loss for all females, and contributed to narrowing the status-related disparity in female reproductive output seen during less arid periods. Although E concentrations were significantly lower in subordinate than dominant females, they were sufficient to support gestation. Absolute E concentrations may owe to androgenic precursors that also attain highest concentrations in dominant dams and may mediate aggression underlying female reproductive skew. Pregnancies terminating in fetal loss were marked by significantly lower P concentrations in mid-gestation and modestly lower E concentrations overall. Consistently high fGCm concentrations further increased across trimesters, particularly (but not consistently) in subordinates and in aborted pregnancies. Environmental stressors may modulate reproductive outcomes in meerkats through their influence on sex steroids and their effects on intragroup competition. The social and eco-physiological factors affecting intraspecific variation in reproductive output, even in obligate cooperative breeders, may be most apparent during extreme conditions, reflecting the benefits of long-term studies for assessing the impact of climate change.