Male orangutans have flat faces due to a combination of evolutionary adaptations and sexual selection. The flat face, along with large cheek pads known as flanges, is a secondary sexual characteristic that develops as males mature. These features are thought to play a role in attracting females and establishing dominance among other males.
The development of flanges and a flat face is influenced by hormones, particularly testosterone. As male orangutans reach adulthood, their testosterone levels increase, leading to the growth of these facial features. The flat face and flanges make the male appear larger and more intimidating, which can help in deterring rivals and attracting mates.
Additionally, the flat face may also have functional benefits. It could provide better support for the large jaw muscles needed to chew tough foods like bark and unripe fruit, which are staples in the orangutan diet. This adaptation ensures that males can efficiently process their food, giving them a survival advantage in their natural habitat.
In summary, the flat face of male orangutans is a result of both evolutionary pressures and sexual selection, serving both social and functional purposes in their environment.