Human Head Evolution With Daniel Lieberman

You spend a large portion of your time staring at heads of people. But have you wondered how they evolved? Harvard scientist Daniel Lieberman, Professor of Human Evolutionary Biology, has been studying human head evolution, particularly the unique features relative to other animals.

I attended his lecture at Harvard tonight, "Heads Up! How and Why the Amazing Human Head Evolved to Be the Way It Is," which is timed with the release of his new book The Evolution of the Human Head.

First, Lieberman took off his shoes. It just snowed again in Cambridge and he doesn't like wearing his boots (or maybe he has some kind of Mr. Rogers complex).

Second, Lieberman talks about how the functions and ontogeny of the human head would boggle any engineer if they had to make something like that. For instance, it's hard to imagine how to design and implement a pea-sized robot that grows into a cantaloupe-sized robot while maintaining survival functionality the entire time.

If robot heads could grow.

Of course, it's not an entirely fair comparison since natural products aren't engineered, but the point is that the head seems overwhelmingly complex to us.

Integration

Not surprisingly (to me), Lieberman's basic recipe for head development is integration. You can view the development of a body part as a series of interactions with atomic parts, which lie at various levels of granularity. For instance, you have proteins, cells, tissues, organs, etc. All the parts constantly adjust to each other, so as to maintain the overall system.


Lieberman uses the concept of skeletal capsules, but he warns us that it's just a hypothesis called the functional matrix hypothesis. Some of his past research was to find correlations between various bone structure sizes in mice, and apparently he found a wicked lot of correlations.



He showed two photos of characters from Harry Potter, and claimed that it showed how each person's nose matches their face. However, it wasn't very convincing, especially his calling Daniel Radcliffe's head narrow when it looks really wide to me, like as wide as Elijah Wood's.

Harry Potter, wide in cranium, narrow in patience.

What would have been better is an example of what would happen without the integration between subsystems--would somebody have a nose covering up their eyes or something?

Harry Potter with development error.

Or the nose would just fall off and run away?

"Nooooooooooooooooose!"

Of course, the environment is also involved in ontogeny--later in the presentation he described an experiment he did with hyraxes, in which they found that if the babies chewed softer food, they had smaller teeth as adults.

Hyrax Potter.

Anyway, the way this complex head integration relates to evolution is that it gives evolution something very hackable. It enables evolution to cause major changes in growth from minor tweaks.

The rest of the talk was a quick tour of the evolutionary history of human heads.

Human Head Uniqueness

So what are the aforementioned unusual characteristics of human heads? Well, the brain case is different, our neck comes out of the bottom of our head, we have vertical foreheads, visible eye whites, external nose, no snout, small mouths, small canine teeth, big ear holes, etc.

Your head is remarkably unusual.

Unfortunately, Lieberman does not have a good theory for one of the human head's unique features: the chin. It's still a mystery.

The Chin: Science's Next Challenge

Image credits:
Robot head: Rodimuspower
Hyrax: Nitzan Cohen Kafri

http://www.science20.com/eye_brainstorm/human_head_evolution_daniel_lieberman-75722

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