Number of friends and self-perception among Jamaican children: the role of attractiveness and fluctuating asymmetry.

The role that physical attractiveness and fluctuating asymmetry (FA), a measure of developmental instability, play in self-perception and peer associations were explored in a well-studied cohort of Jamaican children using a novel research paradigm where subjects were already known to each other for extensive periods of time. The results showed that how attractive a child was perceived by others was significantly positively correlated with self-ratings of attractiveness. Contrary to findings from WEIRD (Western, Educated, Industrialized, Rich, Democratic) samples, the study found a reversal in the sex differences in self-perceived attractiveness and self-esteem, where Jamaican females rate themselves more attractive and report higher self-esteem than do males. Attractiveness also predicts overall popularity, as measured by desirability as a friend and the percentage of peers who choose an individual as a friend. Attractive individuals of both sexes were chosen more often as 'friends'. A significant correlation was also found between an individual's FA and the average FA of those chosen as friends. However, the effect was primarily due to preferences by males for female friends possessing similar levels of FA, which could be an effective strategy in reducing future mating effort.

The distribution of B chromosomes across species.

In this review we look at the broad picture of how B chromosomes are distributed across a wide range of species. We review recent studies of the factors associated with the presence of Bs across species, and provide new analyses with updated data and additional variables. The major obstacle facing comparative studies of B chromosome distribution is variation among species in the intensity of cytogenetic study. Because Bs are, by definition, not present in all individuals of a species, they may often be overlooked in species that are rarely studied. We give examples of corrections for differences in study effort, and show that after a variety of such corrections, strong correlations remain. Several major biological factors are associated with the presence of B chromosomes. Among flowering plants, Bs are more likely to occur in outcrossing than in inbred species, and their presence is also positively correlated with genome size and negatively with chromosome number. They are no more frequent in polyploids than in diploids, nor in species with multiple ploidies. Among mammals, Bs are more likely to occur in species with karyotypes consisting of mostly acrocentric chromosomes. We find no evidence for an association with chromosome number or genome size in mammals, although the sample for genome size is small. The associations with breeding system and acrocentric chromosomes were both predicted in advance, but those with genome size and chromosome number were discovered empirically and we can offer only tentative explanations for the very strong associations we have uncovered. Our understanding of why B chromosomes are present in some species and absent in others is still in its infancy, and we suggest several potential avenues for future research.