SummaryAmong primates, the intense mother-infant bond provides offspring with a lengthy period for learning from an experienced and reliable demonstrator. Since adult life differs for females and males, the expertise of mother may not be equally useful to both sexes of infant, particularly with regard to social relationships. Here, we report on differences between infant female and male stumptailed macaques in learning how to allocate social grooming, using their mothers as demonstrators. Infant females were significantly more socially precocious than males, starting at early ages to groom mothers. Throughout their first year of life, daughters showed more instances of mirroring mothers' behaviour than sons did. In addition, while grooming on their own, grooming durations of daughters to specific partners was significantly concordant with time devoted by mothers to such recipients. We suggest that daughters learn from their mothers how to distribute grooming amongst social companions, while sons primarily use mother as a secure platform to initiate socializing. These results lend support to the idea that mirroring equates with learning and leads to reinforcement of innate propensities for gender roles in primates.

The current study tests a series of evolutionary predictions about the changing opportunities for human male mate choice and female Waist-to-Hip Ratio (WHR) across populations. We predicted that the divorce frequency (that we used as a reflection of the frequency of male mate choice) would be positively correlated with sexual dimorphism in WHRs across human populations. With published data, we built 2 samples, 1 at the international level and the other at the national level. The results showed that sexual dimorphism in WHR is positively correlated with the divorce-to-married ratio in 68 countries worldwide, as well as in the 32 Mexican states. Taken together, our results suggest that the opportunity for human male mate choice, based on female WHR, varies among human populations. We discuss the possibility of connecting this variation to human diversity in divorce practices. We conclude that human male mate choice is a circumstantially conditioned selective process responsible for such dimorphism and suggest that cultural and social aspects are potentially powerful in examining the factors capable of strengthening or weakening the selective process.

Previous comparative research on the evolution of cognition has tested what we call the “altricial intelligence hypothesis”. This posits that a relationship between evolutionary changes in the altricial period length and cognition exists across animal species. However, the evidence available thus far either comes from indirect measurements of cognition or has not been conclusive. We performed a phylogenetic analysis of published data from various sources on 31 homeothermic species to test for an evolutionary association between the degree of altriciality and a direct measure of self-control. For each species, the degree of altriciality was determined based on the residual altricial period (i.e., the time from birth to fledging in birds and to weaning in mammals) on lifespan. The percentage of success in the cylinder task was the measure of self-control. Our results showed that the degree of altriciality covaried positively with the measure of self-control. Based on the results of this study, we sustain that evolutionary changes in the length of the altricial period are associated with evolutionary changes in the cognitive system used by homeotherms to perform the cylinder task.

No abstract

No abstract