Tuesday, June 20, 2006

Homo floresiensis Just Big Enough

Argument over Homo floresiensis making tools despite small brain

There is a real knock down, drag out battle going in anthropology today. It’s ostensibly about Homo floresiensis, the so-called Hobbit. One group insists that this is a new species of tool-using hominids which has "devolved" from ancient Homo erectus, losing stature and brain size because of environmental pressures. The other group insists just as adamantly that the fossil evidence suggests an unusual variant of Homo sapiens afflicted by microcephaly.

Tools have been found near small-brained hominid fossil bones, which suggests that the two finds are related. Can such a small brain support such a complex activity? We’re not talking about trimming sticks to go fishing for termites. We’re talking about tools that the average person today would have great difficulty learning to fabricate.

Whatever the outcome of this particular contest, it should be understood that the subtext is more important than the issue. The real question is whether human evolution is irrevocable. Are we evolving today? Can we evolve in a direction that makes us less human? Many people, including scientists, are uncomfortable with this possibility.

Those who discovered the hobbit believe it evolved from a larger bodied, larger brained ancestor that shrank over time as it was isolated on the island.
The fact that the hominid could still make stone tools despite its shrinking brain suggests toolmaking was key to survival on the island.
This supports the argument that technology helps humans survive changing environments.

CBS’s 60 Minutes recently had a segment on the Hobbit. Science News had a snippet recently. The possibility that humans evolve is big news to many. The idea that they can evolve in this particular way is even bigger news. In fact, as explained by Jared Diamond in Guns, Germs and Steel, humans areevolving rapidly as a reaction to disease more than anything. Increasing population density since the advent of agriculture exposes us to pandemic and endemic pathogens that represent serious challenges to survival and constant selection pressure. Anything that helps protect us from these scourges will come to predominate in the gene pool. In recent centuries we have also been confronted by manmade toxins of various kinds: pollution, lead, chemicals, radiation, medical and pre-medical practices, recreational drugs, and most definitely alcohol. These things also have an effect. They provide differential filters, i.e. selection pressures.

This idea, that we adapt to dangerous aspects of the environment, is, however, more comforting than disturbing. Sure we get tougher, people might think. The disturbing aspect is that we might be sacrificing brainpower as we adapt. Very few adaptations are for free. When salamander populations are trapped in a lightless cave, they develop intensified senses. But, a big but, they lose their eyesight. Evolution moves away from the unnecessary as quickly as it moves toward the advantageous. Bird species can lose their wings. How much more fundamental can you get? If I were a bird, I would be against that.

The ability to run fast seems to be an unalloyed benefit for humans. Suppose that a mutation occurs which reduces running speed, but helps to prevent malaria. It would quickly spread through the population, at least of Africa. The relative benefit is what matters. Humans run fast enough for most purposes. Malaria causes more problems for us than slowness. Natural selection doesn’t care about excellence. A population of thoroughbred horses released into the wild would probably become slower in subsequent generations.

Excellence of thought is also an expensive luxury. Does it pay off? Maybe not. I believe that raw brainpower has actually been diminishing for centuries. It probably peaked in the Neolithic. If you look at the cave paintings of Lascaux, you’ll see what I mean. Who could do that? Within a very small population were the skills needed for making sophisticated hand weapons, tracking animals, identifying edible plants, where and when they appear, making clothing from raw materials, memorizing rituals, and making beautiful paintings in the caves. How many of us today could perform these tasks? The artistic skills may have been byproducts of survival skills. They may also have been used by individuals to advertise their mental fitness.

In either case, the skills became unnecessary as time went by. Agriculture has imposed different selective pressures. Agriculture has also given us substitutes for brainpower. Place and custom propel our daily actions. Writing substitutes for memory. Good teaching practices make us more easily smart. The brute processing power of the brain is no longer as necessary. Maybe Einstein was a throwback.

Suppose, for some reason, that our diets were to become severely restricted for many generations, that malnutrition became common, even in the most sophisticated cultures. What would be the evolutionary response? I think that bodies and brain sizes would become smaller, but those parts of the brain which support necessary learning functions would not shrink. This is essentially the Hobbit’s story.

6/19/2006 11:50 PM

Previous posts on Homo floresiensis:

Hobbits Unleashed 10/12/2005
The Hobbit and Our Self-Image 06/18/2005

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At Thursday, June 22, 2006 9:54:00 AM, Blogger mal said...

and how are they going to prove it one way or the other? The answer is in the brain itself, its structure, density and organization. The bones only only allow us to infer

At Thursday, June 22, 2006 10:04:00 AM, Blogger jj mollo said...

It is possible to argue over every marking on a bone, but there is evidence displayed on a skull about the structure of the brain. We're also getting better at interpreting this information as we learn more about brains and do comparative studies of fresh skulls where we know how the brain was organized.


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