Phylogenetic comparative investigations of sexual selection and cognitive evolution in primates

Abstract

A full understanding of any biological trait requires investigation of its evolutionary origin. Primates inspire great curiosity amongst researchers due to the remarkable diversity across species in both anatomical and behavioural traits, including sociality, sexual behaviour, life histories, neuro-anatomy, cognitive abilities and behavioural repertoires. The study of primates has involved comparative approaches since its inception, however, the necessary tools for statistically investigating the macro-evolutionary processes responsible for current diversity in biological traits have been developed only in the last 30 years or so, namely phylogenetic reconstruction and phylogenetic comparative methods. Amongst a multitude of evolutionary questions that can be addressed by phylogenetic comparative analyses, this thesis attempts to address two in particular, concerning primates. First, chapters 3 and 4 use meta-analysis and phylogenetic comparative analyses to investigate the evolution of large, brightly coloured ‘exaggerated sexual swellings’ in female Catarrhine (‘Old World’) primates. Together, chapters 3 and 4 show that such swellings are signals of temporal fertility, and present evidence to suggest that swellings co-evolved with conditions favouring male mate choice and cryptic female choice, therefore shedding light on the general conditions under which female signals of temporal fertility should evolve. Second, chapters 5 and 6 use phylogenetic comparative analyses investigate the evolution of enlarged brain size in the primate order. Together, chapters 5 and 6 suggest that multiple selection pressures have contributed to diversity in brain size and cognitive traits across primates, including sociality, intra-sexual competition and extended life history. Further, analyses presented in chapter 6 suggest that reliance on learned behaviour is a self-reinforcing evolutionary process, favouring ‘runaway’ increases in cognitive abilities and reliance on culture in some primate lineages, which parallels increases in brain size, cognitive ability and reliance on culture in human evolution.