PubMed · 14244742
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R J MCCALDON. 1964. AGGRESSION.. https://doi.org/10.1177/070674376400900607
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Frequency-dependent selection is an important process in the maintenance of genetic variation in fitness. In humans, it has been proposed that the polymorphism of handedness is maintained by negative frequency-dependent selection, through a strategic advantage of left-handers in fighting interactions. Using simple mathematical models, we explore: (1) whether it is possible to predict the range of left-handedness frequencies observed in human populations by the frequency and the violence of fighting interactions; (2) the consequences of the sex differences in the probability of transmission of hand preference to offspring. We show that a wide range of values of the frequency of left-handers can be obtained with realistic changes of the parameters values. Our models reinforce the idea that negative frequency-dependence may have played a role in maintaining left-handedness in human populations, and provide further support for the importance of fighting interactions in the evolution of hand preference. Moreover, they suggest an explanation for the occurrence of left-handedness among women in this context, namely an indirect selective advantage through their male offspring.
Maternal defense behavior (or maternal aggression) is a highly conserved behavior for protecting offspring that is normally associated with decreased fear and anxiety in rodent dams. Environmental enrichment can decrease indices of fearfulness and anxiety (and elevate novelty seeking) in laboratory animals. This study examined whether enrichment could alter levels of maternal aggression and elevated plus maze performance in lactating mice. One group of female mice was exposed to a series of novel objects for 1.5 months while the other group was not. As expected, mice that had been exposed to an enriched environment showed significantly more entries to and time on the open arms of an elevated plus maze while they were lactating. Enriched mice showed similar maze performances when tested 3 months later in a non-lactating state, even though enrichment had been removed for 3 months. Further, offspring of enriched dams exhibited maze performance similar to that of their dams, suggesting possible epigenetic influences on maze performance. In contrast, no differences in measures of maternal aggression or pup retrieval were detected between enriched and control lactating mice. Together, these results indicate that environmental enrichment has long lasting effects on plus maze performance, but does not alter maternal aggression. The findings also suggest that whatever neural pathways are altered by enrichment do not strongly overlap or regulate those governing maternal aggression.
Red coloration is a sexually selected, testosterone-dependent signal of male quality in a variety of animals, and in some non-human species a male's dominance can be experimentally increased by attaching artificial red stimuli. Here we show that a similar effect can influence the outcome of physical contests in humans--across a range of sports, we find that wearing red is consistently associated with a higher probability of winning. These results indicate not only that sexual selection may have influenced the evolution of human response to colours, but also that the colour of sportswear needs to be taken into account to ensure a level playing field in sport.