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The importance of brain size

The bigger your brain is, the smarter you are, right? As a general rule, sure. But there’s something that worries me.

I may be doing the scientists an injustice here. But from what I’ve read, those working on our ancestors have to base their conclusions on far too little evidence. A statistician would have a fit. In particular fairly small differences in brain size are used to signify genuine difference in intelligence between different (proposed) species. There’s nothing wrong with that. If that’s all the evidence they have then they must do their best with it. The problem comes, as we’ve said elsewhere, when you start actually to believe it.

Birds have long worried me. I understand that birds’ brains are very small. And yet some birds are seriously bright. Surely there will have been huge evolutionary pressure on birds, to get their brains as small and as efficient as possible – far more indeed than on us mammals. Their brains’ weight and bulk are in quite the wrong place for good flying and manoeuvrability. For these you need a small, light, streamlined head. And you need as much of the weight as possible down in the body.

Why did birds lose their heavy jawbones and teeth, and their long bony tails? Presumably for the same reason.

I don’t think we should be surprised if birds’ brains eventually turn out to be much more efficient than ours.

Then there’s the celebrated French intellectual Anatole France. He was obviously very intelligent. But we have it on the authority of Scientific American (SciAm.com) that his brain was but 2/3rds the normal size – about equal to Homo erectus (who we’ve yet to come on to). Another website claims that the author Jonathan Swift (of Gulliver fame) had a huge brain; twice the size of Anatole’s. Swift was clearly very intelligent too, but I’ve seen no suggestion that he was significantly brighter than Anatole.

Now we read that these examples are in keeping with modern research on living people. Human brains come in a wide range of sizes. And their owners come in a wide range of intelligence. But the researchers are finding that there’s only limited tie up between the two.

The Hobbit

This brings us to the strange pigmy folk, Homo floresiensis, whose remains were found on the Indonesian island of Flores. They were only about a metre tall, hence their other name ‘hobbits’. Their brains were tiny, and yet their remains were surrounded with clever stone tools and other accoutrements of fairly sophisticated living.

It’s not for the likes of me to get too involved in controversy. But I think we’re entitled to grumble at the simple certainties displayed by many scientists. It gets them into all sorts of trouble. And in this case we ordinary folk are left to try to make sense of it all. As examples, I can cite Big Bang, Plate tectonics, and the current Hobbit saga, straight off the top of my head.

Theory one is that the Flores folk were Homo erectus people who arrived on the island full sized, some 850 thousand years ago. But food was scarce, and they gradually shrunk so that they could get away with less. Apparently this happens quite a lot when a new species reaches a small island, and becomes isolated there.

But theory two says that humans can’t do this. It goes against all our current knowledge d’you see. The hobbit skeletons so far found must all have been some kind of diseased modern human.

However now that the skeletons are being studied in more detail, theory one seems to be gaining ground fast.

First a palaeo-anthropologist looked at the Hobbit’s wrist bones (Science 6 April 07, New Scientist, 29 Sept 07)), and pronounced them to be too primitive to be from a modern human – diseased or not. Our wrist bones have been adapted to provide a sort of shock-absorber when involved with hard pounding, or in precision work. This hobbit’s wrists had not. The finding fits in very well with him being H. erectus (or H. habilis. I don’t think there’s much difference between the two). Although these guys could make pretty good tools, they would have found it harder going than we stone-age moderns did.

Then came this reconstruction (Science, 7.12.07), which incorporates everything known about hobbit skeletons – except one thing. The woman has been given modern humans’ shoulder blades. Research suggests that hobbit shoulder blades were like those of H erectus. That is to say they were positioned more on the sides of the rib cage than ours are. This would have given their shoulders a more hunched appearance. Perhaps this was the last vestige of our ancestors’ tree-climbing adaptations. I looked up a chimpanzee skeleton on the Internet. To my inexpert eye, it seemed to have the same feature.

Why does all this concern us here?

According to the experts it is simply not possible for such small-brained people to have made the fancy tools that were found. But we have to ask why not? I must emphasise that the following is a personal view.

Brains are expensive things to run as we’ve said before. So there would have been pressure on them to shrink along with the rest of the body if food remained short for a long time. But we can reasonably expect the Flores folk to have lost the less useful parts of their brains first – and studies of modern brains suggest that there will have been plenty of candidates. This is how evolution operates after all.

We can also reasonably expect evolutionary pressure to have worked at least a few tricks, to make the brain that was left more efficient. Finally, we can expect the shrinking process to have stopped at the point where it began to compromise their way of life, or their ability to win a living from their environment. They didn’t have to invent their tools or their way of life. They already had them. They only had to be able to keep them up, which is much easier.

Brain size is certainly hugely important but, as we keep saying, don’t expect things to be simple in this game.