Are Humans the Only Mammals That Blush?

Blushing is caused by the dilation of blood vessels in the facial skin at times 
of embarrassment. Moreover, embarrassment is a highly complex emotion that requires knowing what others are thinking about you, which may well be beyond the knowledge of any other species. It remains a mystery why evolution should favor a signal that's effectively an admission of guilt, though there’s evidence that, after making a social faux pas, people are regarded more sympathetically if they blush. While animals do experience embarrassment, they simply express it in other ways. The animal that exhibits the closest form of blushing is the bald uakari monkey, who deploy their bright red faces as signals of physiological health.