Developmental parallelism in primates

The authors examined a large random sample of skulls from two species of macaques: rhesus monkeys and cynomolgus monkeys. The skulls were measured, divided into age and sex groups and thoroughly analysed using statistical methods. The analysis shows that skulls of young rhesuses are considerably more domed, i.e. have better-developed neurocrania, than their adult counterparts. Male and female skulls, on the other hand, were found to be very similar, which means that sexual dimorphism of the rhesus macaque was suppressed. Both of these patterns are known from the human evolutionary pattern. No such parallelism to the development of Homo sapiens was found in the cynomolgus monkeys. The authors conclude that mosaic hominisation trends may have featured in the evolution of all primates. This would mean that apes were not a necessary step on the evolutionary way leading to the development of Homo sapiens, who may have started to evolve at an earlier stage of monkeys.