Wednesday, 31 March 2010

Human brain mutations.

I stumbled across today, an interesting article on Colin Blakemore's proposition that a single mutation caused a massive development in the human brain. Unfortunately, whilst I can have great respect for Professor Blakemore's previous work, I am not entirely convinced by his propositions.

Let us see what Professor Blakemore has to say:

How Human Brains got bigger.
BBC News interview

Now Blakemore is not saying, Evolution did not happen in these cases, nor that the Evolution that occurred but that it seems to be a mutation that has not been influenced by Natural Selection.

I was asked to give the Ferrier prize lecture at the Royal Society and as this is the society's 350th anniversary I decided to do something special and face up to the issue of the human brain. The question is: why is it so big compared to the brains of our predecessors, such as Homo erectus? Until 200,000 years ago, there had been a gradual increase in brain size among hominins, starting three million years ago. Then, abruptly, there was a remarkable increase of about 30% or so.
Now I've just ferreted out one of my favourite graphs on this situation. People that are familiar with Talk Origins may be familiar with this graph:

As we can see, from the cranial capacities, the trend in general is an increase. Now if we look at the increase in cranial capacity from 250 000 years to now, there is no startling, fantastic changes to be honest. The rate of growth seems to fit the general trend of cranial capacity growth, in that it has increased in the predicted gradient.

How have scientists explained this jump in brain size?

Many have argued that if there was a dramatic increase in brain size, there must have been a fantastic advantage that came with it: improvements in tool construction, more complex language and other cultural changes. In other words, they say simple natural selection explains what happened.

I think Blakemore underestimates the power of tool construction. Making tools is one of the major human accomplishments. We do it in a way which is far more complex than any other animal. We can visualise the shape we want in the rocks, we can use tools made out of bone and wood and this only really occurs later, even after we gain this massive brain. Furthermore, I think he's putting the horse before the cart. The increase in brain capacity allowed society to advance, as can be shown by the level of culture and the relationship to brain size. In all, Blakemore seems to show very little understanding of these matters.

So what is your take on this view?

I think they're fooling themselves. There was very little change in human behaviour at this time, as far as we can see from the fossil record – certainly not one that is explained by a sudden jump in the size of the human brain. These hand-waving arguments about tiny changes in culture explaining the emergence of such a huge change in brain structure just doesn't hold water. It's like arguing that a reptile suddenly developed fully formed wings and then sat around for 200,000 years before suddenly saying: Oh my God, I've discovered I can fly. It's ridiculous.

No Colin, its like letting a child learn how to count, then, once their brain is developed enough, teaching them that 2+2=4. That's a completely fallacious argument. If you never taught a human how to count and then give them a spontaneous equation to solve, you don't expect them to do it. What it is more like is having the reptile using flaps of skin to glide, before eventually, after some evolution, to start to fly. There is no lack of evidence that Homo erectus used their brains to form social connections and advanced tool making. What the difference is, however, like anthropologists including Stephen Mithen have said, is that they were limited in comparison to us. Increase in intelligence led to better social skills, better imagination and better tools, that is clear evidence for a mutation to have a positive effect, which leads to it being selected. All the bullshit about it not being part of natural selection is rather problematic.

So what did happen?

Genetic studies suggest every living human can be traced back to a single woman called "Mitochondrial Eve" who lived about 200,000 years ago. My suggestion is that the sudden expansion of the brain 200,000 years ago was a dramatic spontaneous mutation in the brain of Mitochondrial Eve or a relative which then spread through the species. A change in a single gene would have been enough.

OK, now here are two major problems. Firstly, Colin is making the statement that Mitochondrial Eve or a relative is the one that got this massive mutation that expanded the brain. He puts it at 200 000 years ago. Now I think he's misinterpreted the Mitochrondrial Eve Theory. What the theory proposes is that Mitochondrial Eve is our last comon ancestor. Yes all our DNA can be traced back to her, but this is because other lineages have become extinct in the 200 000 years. Evolution happens at population level, not individual level.

The second problem is that this does not account for our sister species, the Neanderthals. A species with an equivalent and even greater cranial capacity which is missing from Colin Blakemore's argument. I think we can safely establish that Neanderthals are definitely a separate species from our own.

The arguments that Colin Blakemore puts forth are riddled with problems, some of which I think may be derived from his lack of expertise in the field. Whilst I can see that within his own field he is definitely an established expert and if I had the experience I would hesitate to even begin to criticise him, I think he has gone outside his field completely. I've not touched upon the genetics behind this, nor the arguments put forth in published journals testing this problem. I suspect that his standing has led the Guardian and the BBC to take his word as granted in this area without judging the worth of his arguments.

1 comment:

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