'Male baboons have a high potential for aggression. One bite to the genitalia with sharp canines can effectively end a male's mating career,' says Whitham. She and her colleagues spent nearly 200 hours over six months watching a colony of captive baboons at Chicago's Brookfield Zoo.
Penis and scrotum diddling is the culmination of a complex greeting ritual that begins with face pulling and progresses through rump presentation and embracing.
The baboons that were more likely to embrace or exchange diddles also spent a lot of time together, and groomed one another frequently1. Aggressive interactions led to frostier greetings.
Genital fiddling is unique to guinea baboons, but other primates invade each other's space in similarly challenging ways. White-faced capuchin monkeys, for example, stick their fingers up each other's noses in greeting.
But we shouldn't look for a human equivalent, says Whitham: 'Most human greetings do not carry the same potential costs as those exchanged between adult male baboons.'
This male ape has decided to stick with handshaking for the moment...