Why Do Chimpanzees Have Such Wrinkled Faces?

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Why do chimpanzees have such wrinkled faces?Suzanne Sadedin:

It’s not just chimps. Other apes and their babies are wrinkly, too. And baby monkeys. You know who else has a lot of wrinkles? Premature human babies. During the last month of gestation, babies don’t develop much neurologically or physiologically. They just fatten up. Even full-term babies are still kinda wrinkly, but within a few months, they get nice and chubby.

So the question shouldn’t be, why are chimps so wrinkly? That’s easy: they have lots of facial muscles for signaling complex expressions. The question should be: why are humans so strangely smooth? And the obvious answer is: fat. We have a layer of soft, pillowy subcutaneous fat which billows under our skin, making us pleasantly smooth and rounded and hiding our facial muscles.

Compared with other apes, we store a huge amount of fat and have small muscles. The average female chimp has ~3.6 percent body fat; a newborn human infant has ~13 percent, and the average woman has 24 to 31 percent. The sheer amount of fat we store is astonishing; in particular, no other mammal has such chubby babies. Fat storage is thought to be an adaptation that supports our brains. Brains are hugely expensive to build and run. As infant brain development passes through some critical stages, it’s vital that they have enough stored fat to support their growing brains even if their family goes through a temporary food shortage.

But we also store our fat differently. Apes keep their fat internally, mostly beneath the muscles in their torso, so all you can see externally are their big scary muscles. But we humans store a layer of blubber right under our skin. The other mammals who do this are mostly marine mammals trying to keep warm, a fact that led some researchers to speculate that our lineage went through an aquatic phase. However, most researchers don’t think this is likely.

So why do we store fat on our faces? It’s most likely a scam.

If you’re storing fat, you have more food than you need. That probably means you and your family are healthy and good at procuring and using resources. Importantly, you have nutritional resources to support brain development and maintenance. Our big brains are remarkably costly, metabolically. You’re likely to survive the next famine, and maybe, since you obviously have so much bounty, you’ll share some with your friends. And you’re likely to be fertile: up to a point, fat stores are highly attractive in women. In short, having some stored fat means you’re probably a good social partner. The more our evolution revolved around egalitarian social partnerships instead of ape-like dominance hierarchies, the less we needed big muscles to scare our enemies, and the more we needed fat stores to impress our friends.

Once people started looking at fat as a social cue, it would have made sense for evolution to shift the storage location. Instead of hiding our fat beneath bulging muscles, we started to hide our muscles beneath prominent fat stores. When we lost our body hair, our fat stores became even more visible.

Human facial fat in particular overtly advertises good health. It’s highly visible, and impossible to fake. Hollow-cheeked, sunken-eyed, bony-faced, gaunt, wasted, haggard, shrunken, or emaciated—all these terms suggest chronic illness resulting in loss of facial fat stores.

Indeed, it appears fetuses spend the final month of gestation simply preparing for their grand debut. They consume more resources than ever, but instead of maturing during this time, they just get fatter and fatter. Then after birth, they pile on even more fat in the most visible way possible. They’re saying, “Look, mom, my metabolism is awesome! Invest in me!” and “Look, everybody, my family is awesome! Cultivate social ties with us!”

Since we’ve co-evolved with our babies trying to convince us to invest in them via highly-visible facial fat, we respond quite automatically with kindly and nurturing feelings toward chubby-faced entities. We can’t help it. It’s cute. Even older children and adult females retain high levels of facial fat, again eliciting gentleness and empathy from potentially dangerous adversaries. Actually, our whole species shows a suspicious trend toward neoteny, which some researchers have described as a self-domestication process. So much for survival of the fittest: we got survival of the sweetest, cutest, chubbiest munchkins.

And thus evolution, in addition to all the other awful things it’s done, can be blamed for the blobbiness of emojis.

This post originally appeared on Quora. Click here to view.