If a human had a face as red as that of a bald uakari monkey, it might raise concerns about blood pressure - or sunburn. For a uakari, though, it is probably a sign of good health.
Why are uakari monkeys so bald and pink?
The uakari monkey’s facial skin has a particularly thin outer layer, which lacks pigmentation, making the underlying blood vessels more visible. The colour is augmented by the blood vessels being thicker and more convoluted than in other monkeys.
The effect is most pronounced in male uakaris, which also possess large temporal muscles that reinforce the overall effect by making their faces bigger.
Facial redness is thought to be an indicator of a male’s health, which is assessed by females choosing between potential mates.
Bald uakaris are particularly susceptible to two blood-borne parasites, and it may be that the redder a male’s face, the fewer parasites he harbours.
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Image and video by Getty