Is brain size an indicator of intelligence?

Discussions unearthing human history including cultural anthropology, linguistics, etc.

Is brain size an indicator of intelligence?

Postby pantodragon on February 23rd, 2013, 12:17 pm 

When palaeontologists are reconstructing human prehistory and are attempting to fit the various bits of hominid skeletons they have found into some sort of evolutionary story, they use brain size as a measure of intelligence. They assume that modern people’s very big brains are due to the fact that they are the most intelligent creatures on Earth so that one of the major things they are looking for is the evolution of the big brain.

What puzzles me is the idea that brain size should be a measure of intelligence.

Whales have bigger brains than humans, but, as far as I understand it, that is put down to the fact that they have bigger bodies to control. But Dinosaurs had notoriously small brains even though some of them could rival whales for size, so that does not seem to tie up.

Then there is the case of the person who led a perfectly normal life, no social or any other problems, and got a university degree, and then it was discovered, I think accidentally, that this person had only a thin layer of brain tissue lining the skull and the rest of the cavity was filled with water. So this also seems to make nonsense of the idea that a larger brain means greater intelligence.

Then if one considers the world of computers: in the computer world small is beautiful i.e. all the effort is directed towards making computers smaller yet more powerful, and the best computer is the one that achieves the minimum size without sacrificing any power. Partly, of course, minimization is a matter of the hardware being miniaturised, but that is only part of the story. The other thing is making the software more efficient, so it’s not just about the amount of hardware the computer has, but how well it uses it. So, in the computer world, there is no direct link between size and power.

There is a series of children’s fantasy books called The Astrosaurs, by Steve Cole, in which the dinosaurs left the Earth before the meteorite hit. They supposedly developed space travel and are now living and going on evolving in some other region of the galaxy. In the introduction the author explains this achievement by saying that, though the dinosaurs had small brains, they used them well.

I wonder, then, if there is any justification for thinking that the big brain of humans has anything at all to do with intelligence. And if one discounts the relationship between intelligence and brain size, I wonder where that will leave palaeontology.

If one takes the view that developing a larger brain may, in fact, denote a REDUCTION in intelligence, denote a species that is using its brain badly and is therefore having to develop a bigger brain just to survive, then one can completely re-interpret the finds of palaeontology: what the palaeontologists may be finding is evolutionary dead-ends. Evolution is littered with oddities that became extinct for some reason or other. One has to wonder if palaeontologists are doing anything more than unearthing ape-like oddities that became extinct because of loss of brain efficiency, which is to say, they died out due to stupidity. It may be that few, if any, of the finds of palaeontologists have anything at all to do with human evolution.

It seems to come down to the old matter of the ‘missing link’. There are relatively recent remains of creatures that can definitely be identified as human, with the big brain and all the attributes that we associate with ourselves – always allowing for insignificant variations, and then there are earlier creatures which come in a variety of shapes and sizes, have large brains compared with their nearest ‘relatives’ i.e. the apes, (and lemurs), may have walked upright, may have used primitive tools (there are numerous animals and birds that use tools) etc, but there is no justification for linking these other creatures with humans – more data, much more data, and more understanding of the brain is needed. And that leaves one with the conclusion that, so far, there is no evidence for the idea that humans evolved from some ape-like, or lemur-like ancestors. The whole question of where humans came from is still wide open, still a mystery.
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Re: Is brain size an indicator of intelligence?

Postby moranity on February 23rd, 2013, 1:06 pm 

cro-magnon man, a version homo-sapiens who resided in fair europe around 25 thousand years ago, had a brain size about 10 % above modern man, if memory (in my inferior brain) serves me. Also, it seems neaderthal (awwwwww) had a brain size about 5% bigger than modern humans. Both of these had comparable body size to us.
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Re: Is brain size an indicator of intelligence?

Postby neuro on February 23rd, 2013, 2:35 pm 

It seems more reasonable to consider that intelligence parallels the number of neurons in the brain, and possibly (and more interestingly) the number of glial cells (which may permit neurons to establish a higher number of synapses).

At first sight, one would guess that brain size and number of neurons (and glial cells) should be paralleled by brain size, but the relation does not appear to be so tight.

A more relevant aspect appears to be the "size" of associative (and particularly prefrontal) cortex. Again, however, the point is number and complexity of circuits rather than size. Thus, the thickness of such cortical areas appears to be relevant, and especially its "surface area".

In fact, the cortical layers constitute a kind of mantle, and the relevant "size" is the surface area of such mantle. A major difference between human and any other brain is in the complexity and depth of cortical foldings (which increase surface area).

Forrest may help us in this, but I bet paleontologists don't care so much about skull volume alone, but also consider the signs, in skull bones, of cortical convolutions.
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Re: Is brain size an indicator of intelligence?

Postby moranity on February 23rd, 2013, 2:39 pm 

indeed, the analysis of neanderthals and cro-magnon skulls is said to indicate that certain areas associated with intellegence are larger, if i remember the info right, it was posted on here a while back, maybe by Forrest.
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Re: Is brain size an indicator of intelligence?

Postby pantodragon on February 25th, 2013, 11:50 am 

neuro wrote:
A more relevant aspect appears to be the "size" of associative (and particularly prefrontal) cortex. Again, however, the point is number and complexity of circuits rather than size. Thus, the thickness of such cortical areas appears to be relevant, and especially its "surface area".

.


Which seems to me to be pretty much saying it's how you use it, not the size. One wonders if science allows, or knows, whether or not the complexity of circuits is something that can change through, such as, education/personal development.
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Re: Is brain size an indicator of intelligence?

Postby moranity on February 25th, 2013, 12:15 pm 

pantodragon wrote: One wonders if science allows, or knows, whether or not the complexity of circuits is something that can change through, such as, education/personal development.

hi PantoDragon,
yes we have observed such changes.
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Re: Is brain size an indicator of intelligence?

Postby neuro on February 25th, 2013, 1:57 pm 

pantodragon wrote:Which seems to me to be pretty much saying it's how you use it, not the size. One wonders if science allows, or knows, whether or not the complexity of circuits is something that can change through, such as, education/personal development.


It does indeed.

Many studies (iniially anatomo-pathological, post-mortem; now mostly neuroimaging, PET, MRI, fMRI) have shown how the thickness and volume of specific areas of the cortex can change depending on use, and surely can be altered by pathology (I don't mean mental retardation alone, but also schizophrenia, depression, and similar)
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