Uakari Monkey & The Origin of Blushing

It is said that humans are the only animal that blushes.

Uakari monkeys have bright red faces and are unusual among primates for it. But they don't blush. I don't know how anyone would be able to tell even if they did!

The evolutionary origin of their bright red faces is as about as big of a mystery as why humans blush.

One theory about uakari monkey facial redness is that it's a sexually selected trait associated with testosterone. A related theory says it advertizes health.

These neat-o small (9 pound) monkeys live in South America, really are that white (at least this subspecies), and are reputed to be monogamous.

Uakaris, along with bearded saki monkeys, might be the only primates other than humans that form large groups made up of monogamous pairs. These monkeys are NOT well studied so they may not actually be monogamous. The ARKive site has some really great footage of uakaris.

Blushing, like any other nonverbal behavior with communicative value, fascinates me both academically and personally. You see, seldom am I embarrased to speak in public; it's an occupational hazard after all, but, every once in a while a totally uncontrollable and horrible blush sweeps across my face, neck, and upper chest. I can feel my skin heat up, sometimes I sweat. What is weird is that rarely in such instances do I actually feel embarrassed, yet there it is blazing, bright freaking red, red, red. I even blush alone. I think it must be related to hot flashes, but I am way too young for that. To add insult to injury, I am incredibly pale-skinned, so even the slightest blush can be seen from afar, like the fire truck roaring down the street yelling at everyone to get the hell out of its way.

Bright red faces are not unknown in the animal kindom. Primates, and famously humans, become red with anger. Here the red signals, indeed, SHOUTS: Get away!!!

I would argue that reddened faces during anger make it possible for socially grouping animals to maintain those groups in spite of frequent conflicts which inevitably emerge whenever individuals must live together and use the same resource pool. Having a signal that indicates to everyone else that you are pissed off and which prompts others to get away from you protects everyone from fighting, injury and group disintegration.

Why we would show rage on our faces rather than some other part of the body intrigued Darwin, who wrote about that and the subject of emotion and facial expression in The Expression of the Emotions in Man and Animals. I love picking up the book and reading it but I find it incredibly frustrating because it is mostly (80% I'd say) descriptive with little evolutionary theorizing about why animals and humans have the facial expressions they do, including that of shame. Needless to say, in the last few days of pondering my impending unemployment, I thought about writing a textbook about nonverbal communication across animal species! I found out when prepping my nonverbal behavior seminar that there isn't anything on the market that does even a decent job of reviewing the relevant research. Much of what exists is pop-psychology rubbish.

But, back to the point. Rage and shame are not the same, but maybe both work to hold groups together. Darwin didn't offer up a compelling theory of why people, alone in the animal kingdom, blush. Perhaps, as he hints, it has something to do with us being one of the few species that has a self-concept. In order to blush, you have to know you exist independently from others. This is why humans don't tend to blush until about age two, right around the same time they "individuate" and realize they are not the same person as mom and dad. Congenitally deaf and blind people blush.

The one theory that Darwin presents and subsequently rejects in The Expression argues that the Creator (today we'd call it an Intelligent Designer) made us blush when we do something that violates the rules of our social group so that others will know we regret it. I like the theory a bit. Yet like Darwin, I think evolutionary forces made it so. If a signal makes others want to keep us on the island when we screw up, such a signal could evolve through natural selection. It could also have arisen through group selection, sexual selection, or random genetic drift.

You know what's interesting? The face becomes red and then we feel the heat from the flush. Thus, others see the signal before we even know we're blushing.