Historically, people looked at androgens, such as testosterone, to determine rank. A deterministic model arose from these studies claiming that testosterone drove behavior. However, closer examination showed a contradiction. This has led to more dynamic research focusing on testosterone level as a mirror of success and defeat in social interactions. Comparisons between different species point to the complex interplay of hormones and behavior.
Hamadryas baboons form harems with one male aggressively guarding multiple females.
This allows the dominant male sole access to mating rights, ensuring that his genes are passed on to the next generation. A closely related species, the Anubis baboon, lives in a more egalitarian social system with multiple males and females residing in the same troop. Dominant males will only guard a female when she is in estrus and ready to breed. These contrasts in social order are interesting, but there are also telling differences in their hormonal levels. Hama-dryas constantly maintain high levels of testosterone, while the Anubis' levels only increase during female estrus.