To Each According to his Need? Variability in the Responses to Inequity in Non-Human Primates

While it is well established that humans respond to inequity, it remains unclear the extent to which this behavior occurs
in our non-human primate relatives. By comparing a variety of species, spanning from New World and Old World monkeys to great
apes, scientists can begin to answer questions about how the response to inequity evolved, what the function of this response
is, and why and how different contexts shape it. In particular, research across non-human primate species suggests that the
response is quite variable across species, contexts, and individuals. In this paper, we aim to review these differences in
an attempt to identify and better understand the patterns that emerge from the existing data with the goal of developing directions
for future research. To begin, we address the importance of considering socio-ecological factors in non-human primates in
order to better understand and predict expected patterns of cooperation and aversion to inequity in different species, following
which we provide a detailed analysis of the patterns uncovered by these comparisons. Ultimately, we use this synthesis to
propose new ideas for research to better understand this response and, hence, the evolution of our own responses to inequity.