Why Do I Have a Face?

We are faced with both an immensity of knowledge and an immensity of ignorance in this world. As young children, we ask questions of our parents and teachers until we get no more answers. At this point, either our curiosities overtake us, and we become little experts ourselves in the particular questions we like to ask; or, sadly, our curiosities sometimes run dry when the effort to find out seems to outstrip the reward of doing so. Sometimes, we even forget that questions are there to be asked.

I was once standing with a friend on a bluff that overlooks the Pacific at Half Moon Bay in Northern California. We were telling stories, and the water reminded my friend of a forgotten mystery. As a child, he had gone to the beach with his father and asked him why the water was salty. His father said that God had first created the seas of the world, then decided to bathe in them. While he was in the water, naturally, he peed, and the wine-dark seas were filled with salt.

The story had the shape of a myth, and as I laughed I realized how many myths must have originated with parents who were just trying to shut up their overly inquisitive kids. “Why does the leopard have spots? Well, kid, let me tell you a story…”

So, I goaded my friend, did he know now why the sea is salty? He hesitated to think… No, he had never found out. Somehow, the just-so story had done its trick, and he had forgotten to wonder further about the salt in the sea.

As it turns out, the reason why there's salt in the oceans is well-known. The oceans didn't start out salty. That part of my friend's father's theory was correct. Our evolutionary ancestors evolved in oceans that had salt content more similar to that of one's own blood plasma. The fractions of different salt ions (potassium, sodium, and chloride) in one's blood in fact still mirror the fractions in seawater but are diluted to about 1 part in 4. That's to say that we, and other vertebrates, have blood that is basically just modified seawater from a long time ago.

However, over geological time, rainwater leeched the salts from the ground and drained with them to the oceans. Once there, the salt was stuck — it cannot stay dissolved when ocean water evaporates — so the oceans became saltier and saltier, while our blood stayed the same.

Ironically, our urine has a high salt content because we have expended a great deal of effort to regulate the concentration of salt in our bodies to within the levels that existed when we evolved. If the salt content of our blood becomes much higher than that of ancient oceans, we die. The salty-ocean myth had it backwards, as usual: the oceans didn't become salty because of pee; pee was salty because of the oceans.

It's easy to forget how contingent our experience is on evolutionary time. Actually, it's incredible: our pee is salty because of what the ocean was like 500 million years ago. What seems like a fact of life at one point had to struggle merely to become a fact. Sometimes the fact came about by an accidental miscarriage of nature or by a now unreconstructable event, but often enough we can take pretty good guesses about its genesis. For example, one theory goes that we're bipedal because food supplies were sparsely distributed on African savannas. Bipedal walkers could traverse those distances more efficiently, and bipedalism spread across the early hominid species.

Yet, on the topic of recent human evolution, I've become pretty familiar with the range of outstanding questions. One can be sure that there is a gamut of theories and connected questions about the form of the human hand, the shape of the human larynx and mouth, the size and shape of women's pelvises. However, every once in a while, I come across a question that I never knew could be asked.

So I have a question: Why do we have faces? This question falls firmly in the category of question that seems so blindingly, face-slappingly, obviously stupid and unanswerable that I never would have thought to wonder about it. Admittedly, I'm not really sure it's the kind of question a child would ask. It seems completely reasonable to say that it's just the way it is.

It may not be something you've ever thought about before, but there are actually animals that don't have faces. Sea sponges — they're animals — and are absolutely faceless. They don't have very specialized bodies either and survive by filtering nutrients through their outer walls. Thus, having a face is a contingent evolutionary state: plants certainly don't have them. Consequently, there was a time when there were no faces on the planet, and then, a few hundred million years ago, the first face appeared. Why? There must be a reason.

What happened is that animals started to specialize their body plans. Instead of taking food in through the entire body surface, animals developed digestive tracts that moved food from the mouth to the anus. (The mouth and anus were twins separated at birth.) ’

Most animals, and especially foraging animals, spend most of their waking hours trying to find food and put it in their mouths. So it behooved nature to put sensory organs near mouths. (It would be extremely difficult to eat if your eyes were on your back.) Once the sense organs were arrayed around the mouth, it reduced wiring to build a processing station nearby called the supraesophageal ganglion (i.e., the "above-eating entrance'' nerve cluster) whose role was to sort out what the sensors were reading.*

This ganglion, by the way, was the progenitor of the brain. It was mushy and vulnerable and needed to be protected. Eventually, a rigid cap evolved around it, first one made of cartilage, and then one made of bone (in a fish, the first animal to have bones). At that point, we were unalterably enfaced, as we drifted and fed ourselves in the salty sea.

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