Negative correlation between mean female age at first birth and rates of molecular evolution in primates, with predictions of the reproductive age in early hominins

Abstract

mtDNA-based phylogenetic trees of the order Primates were constructed by the minimum evolution (ME) and maximum likelihood (ML) methods. Branch lengths were compared with the mean female age at first birth in the taxa studied. Higher reproductive age in females triggers a lower number of generations through time and, on average, at the molecular level smaller evolutionary distances between related taxa. However, this relationship is significant when the phylogeny is resolved by the ME method rather than the ML method. Reliability of the minimum evolution approach is discussed. In contrast to most studies, the ME tree recovers Tarsius bancanus (Tarsiiformes) as a member of the Strepsirrhini, which phylogeny is supported by a strong branch length-reproductive age relationship and which is proposed as a novel heuristic method to test phylogeny. However, branches of certain taxa on the constructed phylogenetic tree show anomalous lengths relative to the mean female age at first birth, such as e.g. the human branch. As estimated in this paper, early members of the human lineage have likely reproduced at higher rates than modern humans, some forms possibly giving first birth at the mean age of 10-12 years, which is more comparable to the mean age at first birth in extant gorillas than to that typical of living humans and chimpanzees. Probable early reproduction in human ancestors is also supported by the comparably more evolved mitochondrial DNA in Denisovans than in modern humans, and by a smaller body mass in most fossil hominins, which often triggers fast maturation in primates.