A sexually mature male with cheek flanges, throat pouch, and very long fur.
Why would a sexually mature male orangutan want to look too young to father children? Just ask male dung beetles or goby fish. All these species have two types of males: big, aggressive ones that elaborately woo females and smaller sneaker males who, well, sneak behind the backs of the bigger ones. Both can end up successful fathers.
Male orangutans become sexually mature around age 10, but some will stay in arrested development for up to 20 years, even after fathering children of their own. These immature-looking males don’t have the broad cheek flanges, throat pouches, and long orange hair we normally associate with male orangutans. They also don’t produce the long calls that mature-looking males use to attract mates. Even with none of these secondary sex characteristics, male orangutans can get mates and have children. A previous study that tracked an orangutan population in Sumatra for 27 years found that 6 of 11 new babies were fathered by the immature-looking males.
A new paper in the American Journal of Physical Anthropology models how arrested development works in a population. The key is whether dominant, mature-looking males monopolize all female attention. In Sumatra, the dominant male will attract all the females in his area but only mate with one. They can’t tell whether young, adolescent females are actually ready to have offspring, so the dominant male will prefer to mate with a female who’s given birth before. That’s where the immature-looking males come in. They will take the chance, whatever chance they can get with young females, and it pays off: the first born offspring of most females are sired by these immature-looking males.
The nonthreatening look of these males is how they sneak in for access to the females. When two dominant males encounter each other, violent and even deadly fights can ensue. But the dominant males will tolerate immature-looking ones who hang around their territories. In the animal kingdom, strength and aggressiveness isn’t the only evolutionary strategy—being sneaky works too.
[via Hominid Hunting]
Image via Wikimedia Commons / David Arvidsson