Nature & Environment
Studying mammals: The social climbers
...De Brazza's guenons draw attention to their white-bearded dewlaps by shaking their heads when signalling aggression [p. 271], and dominant male vervet monkeys subdue subordinate males by flaunting their blue scrotums and red penises [p. 270]. The ability to use facial expressions has increased the complexity of social interactions between primates; therefore the brains of...