The human brain conundrum

[Asolepius]

I can demolish most arguments against evolution, except for this one. I am told that humans developed bigger brains than our ancestors because they conferred a selective advantage. Sounds obvious doesn't it? Yet I am also told that brain size is not related to intelligence in humans. So we have the necessary variation on which selection should work, but it doesn't seem to be working. Does anyone know the answer? Maybe it's obvious, but my brain is too small to see it.......

[Matabiri]

Originally posted by Asolepius
I can demolish most arguments against evolution, except for this one. I am told that humans developed bigger brains than our ancestors because they conferred a selective advantage. Sounds obvious doesn't it? Yet I am also told that brain size is not related to intelligence in humans. So we have the necessary variation on which selection should work, but it doesn't seem to be working. Does anyone know the answer? Maybe it's obvious, but my brain is too small to see it.......

What is meant by "intelligence"? The ability to do IQ tests? What's that got to do with survival?

I suspect the metric is wrong.

[Yaotl]

Because it isn't the size that matters, it's how it's built? There's something to be said for the size of our melons, sure, but it's more important that the parts of the brain we have developed are used for what we need to use them for.

[Asolepius]

Originally posted by Matabiri
What is meant by "intelligence"? The ability to do IQ tests? What's that got to do with survival?

I suspect the metric is wrong.
You are quite right, and I'm no more a fan of IQ tests than you are. But something has driven the growth on brain size - what is it? For example, the brains of Einstein and Descartes are widely reported to have been not particularly big, but these were clever people by whatever yardstick you want to use. Perhaps the variation in human `intelligence' in the present population is not actually very wide, and not enough to have any strong selection effect, and the selection is really acting on a very few gross variations.

[hgc]

I don't see why relative brain size intraspecies is necessarily analogous to relative brain size interspecies. There's a hell of a lot more difference between different species' brains than size. Look at dogs. You can fit a whole Chihuahua inside a St. Bernard's brain pan. But those little yappers are just as smart.

[Asolepius]

Originally posted by hgc
I don't see why relative brain size intraspecies is necessarily analogous to relative brain size interspecies. There's a hell of a lot more difference between different species' brains than size. Look at dogs. You can fit a whole Chihuahua inside a St. Bernard's brain pan. But those little yappers are just as smart.
Brain size per se is not the criterion, it's size in relation to body. A Diplodocus brain was of reasonable size in absolute terms, but it had 50 tonnes to control. I am prompted to ask this because most Thursday evenings I have an argument with a creationist friend. Actually she hasn't thought of this one yet, knowing nothing at all about science, but I need some ammunition!

[Asolepius]

I just found this paper. (http://www.cpa.ca/Psynopsis/rushtxt.htm) It is a contentious field, but these authors say "The evidence is overwhelming that ........ differences in mental abilities are related to differences in brain size. " Just a few minutes of web searching shows that this is a very complex and hotly contested area of science.

[Pragmatist]

Originally posted by Asolepius
You are quite right, and I'm no more a fan of IQ tests than you are. But something has driven the growth on brain size - what is it? For example, the brains of Einstein and Descartes are widely reported to have been not particularly big, but these were clever people by whatever yardstick you want to use. Perhaps the variation in human `intelligence' in the present population is not actually very wide, and not enough to have any strong selection effect, and the selection is really acting on a very few gross variations.

It seems to me that it's obviously an issue of form versus function.

The form of the brain (i.e. the size) is only part of the total equation. There may be a correlation in part, but other factors can influence it. For example the interconnectivity of neurons. A smaller brain with denser, more highly connected neural pathways may process much more efficiently than a physically larger brain with fewer connections or lower neuron density.

However, despite the fact that size does not absolutely determine connectivity, it follows that a larger brain has potential for greater connectivity. But then you start to run into other factors that can influence that. For example, more neurons require more resources (i.e. food, oxygen). And the increased demand requires increased infrastructure to process and deliver them to where they are needed. Similarly in parallel an enhanced infrastructure for dealing with the removal and processing of waste is required as well. In addition, a larger neck is needed to support the extra weight, extra bone is required to support it and so on.

Imagine the evolution of a city. It starts out as a few houses, and people build power and water supply systems and drainage to handle them. Then some more people come along and add more houses. The supply/waste system needs to be expanded. But there comes a point where it becomes inefficient to haul all the garbage from say the centre of the conurbation to the outskirts. At that point it makes sense to distribute the processing of supplies and waste and to set up localised supply and disposal sub stations. But as soon as you do that, you have increased the efficiency of the system beyond its immediate requirements. Therefore if there is a need to add just a few more houses, it makes sense to squeeze them in in the same areas and simply to use up some of the spare capacity of the existing infrastructure, rather than expanding the entire conurbation. The next stage is where the demand again exceeds supply of fresh land. More houses are needed. If the local infrastructure can support more houses you demolish the larger estates that were originally built and replace them with many more smaller, denser houses. The system reaches

Therefore the evolution of the city follows a pattern:

1. Initial size increase with large estates of low density. (Low efficiency)

2. Increase of density with no increase of size. (Increase efficiency)

3. Reorganisation to smaller estates with higher density (High efficiency).

4. Ultimately, further increase in size.

In the longer term there will be an overall correlation between size (growth) and total capacity/capability, but at specific points along the way there may be significant increases in capacity without any increase in size at that point.

Finally, in evolutionary terms, does the abstract intelligence of an Einstein increase survival prospect? That is what evolution aims for. In evolutionary terms Einstein may be a useless dead end.

[Asolepius]

Originally posted by Pragmatist
It seems to me that it's obviously an issue of form versus function.

snipped

In the longer term there will be an overall correlation between size (growth) and total capacity/capability, but at specific points along the way there may be significant increases in capacity without any increase in size at that point.

Finally, in evolutionary terms, does the abstract intelligence of an Einstein increase survival prospect? That is what evolution aims for. In evolutionary terms Einstein may be a useless dead end.
You have illustrated the level of complexity surrounding this question. It could well be the most complex question in evolution. But I will have a hard time explaining it to my creationist friend! To go back to my original question, I had assumed that there was no evidence for a correlation between brain size and mental ability (however you want to define that), but it seems there may be some evidence. It's not by any means the only factor, and the picture is confounded by the plasticity of the brain, even quite mature ones. Training can improve cognition even in the elderly. So brain wiring, which is clearly genetically determined, can be highly modified by stimulation. But to summarise, evolution must have driven the increase in brain size, as well as the structural changes which are known to be related to processing ability. I am just interested in the associations between population variability of these factors, and the trend towards better brains.

[Dymanic]

Originally posted by Asolepius


Sounds obvious doesn't it?
I don't think anything about this is obvious, and perhaps what is least obvious is the fact that nothing about this is obvious.

The capability our brains have to throw a conceptual net over a writhing swarm of non-obviousness, haul it in, and wrap it up into a neat little bundle we can sling around as though it were the most obvious thing in the world -- surely that must be a lot of what goes into making us what we call intelligent. At the same time, it is exactly this same capability that gives us such amazing potential for stupidity.

[Soapy Sam]

One theory for the rapid evolution of human brains is sexual selection. If one sex finds big brains sexy, mates with big brains get selected. If both sexes find big brains sexy , you have a forced evolutionary trend. Other classic examples are peacocks' tails and Great Irish Elks' antlers.

In short, the explosive evolution of human brains may have nothing to do with intelligence- at least at first. But once language developed and the ability to communicate, it may be that intelligence itself became the sexual attractant.
At that point we have a meme / brain self reinforcing system selecting it's owners for it's own advantage.
The reactor just went critical.

A check on this process would be the female birth canal, which can't evolve indefinitely to pass larger skulls without a major tradeoff in the mobility of women. And the growth of the brain does seem to have reached a limit. Neanderthal brains were larger than ours- (though maybe they were less adaptable) , but human brains have not grown much in the last 50,000years.

Some results of sexual selection for big brains may have been the short human gestation period (compared to body mass and to other large primates) and the fact that human infants are clearly premature even at ten months, by comparison with most animal infants.

I wonder, if Caesarean birth continues to spread and premature intensive care improves, whether the tendency for human brains to grow may restart?

[Xeriar]

Originally posted by Asolepius
I can demolish most arguments against evolution, except for this one. I am told that humans developed bigger brains than our ancestors because they conferred a selective advantage. Sounds obvious doesn't it? Yet I am also told that brain size is not related to intelligence in humans. So we have the necessary variation on which selection should work, but it doesn't seem to be working. Does anyone know the answer? Maybe it's obvious, but my brain is too small to see it.......

Microcephalics (pinheads is the non-PC term) are of subnormal intelligence.

Intelligence depends on a number of factors, not all of which we understand.

Beyond size (and thus, raw brain cell count) there is also connectivity - the number of connections between each neuron... In humans, this ranges from 1,000 to 100,000 per brain cell.

I think these higher counts are correllated with the twisting and warping of the brain, causing the wrinkleed state. If this doesn't happen, severe mental retardation can result if it becomes too widespread, I'm not sure what the medical term is. Really old Discover magazine article.

Another factor is transmission speed. This is fairly constant in vertebrates given myelin coating, I think.

Many other factors may come into play, probably more than we currently understand, but size still matters.

[Interesting Ian]

Originally posted by Asolepius
I can demolish most arguments against evolution, except for this one. I am told that humans developed bigger brains than our ancestors because they conferred a selective advantage. Sounds obvious doesn't it? Yet I am also told that brain size is not related to intelligence in humans. So we have the necessary variation on which selection should work, but it doesn't seem to be working. Does anyone know the answer? Maybe it's obvious, but my brain is too small to see it.......

One devastating argument against evolution is the fact that we are conscious.

[Dancing David]

Less controversial than you might think, the size of the human brain starts in the neotany of the human baby, the neotany of the human baby starts in the upright posture of archaic homonids, the narrower pelvis means that the brain has to grow more after birth , rather than before.

The unique wiring of the human brain is only sort of controversial, it would appear that humans were adaptred to walk before they developed the higher cognitive skills.

[Dancing David]

Originally posted by Interesting Ian
One devastating argument against evolution is the fact that we are conscious.

Oh my god! That just makes so much sense, now I understand! It is all so clear. No organic being could ever develop awareness of it's surrounding , much less develop awareness of it's awareness.

[Jyera]

1. Size of skull is a result of what stuff is in it.
Human have (a) Brain Stem , (b) Cerebellum (c) Cerebral cortex .
Note that each component has significantly new function. It follows that the container has to increase in size to house them.
If humans at some point develop another new and significantly different component, the size is going start to jump "sudden" on an evolutionary time scale.

2. After Cerebral Cortex, what is next ?
Perhaps as Soapy Sam suggested, with Caesarean birth and quality health care, there is chance to overcome the "restriction" of the for the development of the next significant component in our brain

3. There is "Critical Mass" to consider.
An animal that has 40% Brain Stem, 59% Cerebellum and only 1% Cerebra Cortex may not be much different from one that has only 0% cerebra Cortex. But as the cerebra cortex grows bigger as the species evolves, there comes a point in evolution that it reaches a critical mass in terms of the size of the Cerebral cortex .
And the selective advantage becomes clear and significant.

4. The bigger the brain-space(skull), does not imply we must use all of it. This misconcept might be the reason some people associate bigger brain with intelligent.

5. But bigger Skull , does mean bigger space to put alot of "nonsense". This gives a chance of lots of "nonsense" to happen. And some of these "nonsense" holds the potential to result in innovation and thus improved chance to excel.
Eg. Painting, and drawing of animals in cave. It probably started as non critical, unimportant, energy wasting pursue. But it gradually developed into a powerful form of communication, and then written language.
Eg. Thinking, Analysing, planning, imagining. All these seems unimportant during pre-historic time. When the bigger the muscle the better. Caveman envy the muscle of the lions, until they start to appreciate their own cunning.

[Dymanic]

Originally posted by Soapy Sam


One theory for the rapid evolution of human brains is sexual selection. If one sex finds big brains sexy, mates with big brains get selected.
Maybe what was being selected for was just bigger heads.

[Soapy Sam]

Perfectly possible. Or flat foreheads. My point is that explaining brain growth solely in terms of brain function may be missing the truth.

[Asolepius]

All very interesting contributions. Actually I did meet my creationist friend last night but avoided triggering any discussions! I had forgotten about the skull size and birth canal problem. Maybe we have reached a practical limit, which may be confounding the correlations I am looking for.

[Dancing David]

Originally posted by Soapy Sam
Perfectly possible. Or flat foreheads. My point is that explaining brain growth solely in terms of brain function may be missing the truth.

Quite right! I feel it is more likely a product of the narrowing pelvis and increased communication.

Bird brains function very much like human ones, they have binocular color vision and all that.

[epepke]

Originally posted by Asolepius
I can demolish most arguments against evolution, except for this one. I am told that humans developed bigger brains than our ancestors because they conferred a selective advantage. Sounds obvious doesn't it? Yet I am also told that brain size is not related to intelligence in humans. So we have the necessary variation on which selection should work, but it doesn't seem to be working. Does anyone know the answer? Maybe it's obvious, but my brain is too small to see it.......

That's just a sop, a probably futile attempt not to be accused of racism or sexism. It's sort of true, because the variations in intelligence dwarf the differences in brain size amongst modern humans. But basically, bigger is better, and more wrinkley is better, too.

But if you're really smart, you'll lie about it, because you probably want to get laid, too.

[Jyera]

Originally posted by epepke
...snipe...
But if you're really smart, you'll lie about it, because you probably want to get laid, too. While I agree with this, I find it contradicting. Being smart ought to be seen as giving better chance for survival. So why is it that it(very smart trait/gene) is avoided, as if it is an undesirable trait.

[Yahweh]

Originally posted by Asolepius
I can demolish most arguments against evolution, except for this one. I am told that humans developed bigger brains than our ancestors because they conferred a selective advantage. Sounds obvious doesn't it? Yet I am also told that brain size is not related to intelligence in humans. So we have the necessary variation on which selection should work, but it doesn't seem to be working. Does anyone know the answer? Maybe it's obvious, but my brain is too small to see it.......
I thought our brains have become smaller than our previous ancestors. As long as intelligence isnt related to big brains, then you can safely assume that a smaller brain would equate to more efficient usage.

[Eos of the Eons]

Well, I look at it this way. We don't have claws, or fur, or sharp teeth, and we're not built for speed...

What can we rely on to ensure our survival? Our brains that is. We have to be smart enough to find food, shelter, rear young, etc.

So the ones with more intelligence survived better in our species, and possibly in all species. We have a large brain to body mass ratio. Look at all the things we can do that other species cannot.

Women have a larger brain to body mass ratio compared to men. Does that make women smarter? No. Not really. I think it has more to do with the functions we need to perform, so it affects how our brain is "made".

So a really dumb person can have a large brain, but still be lacking something in there (wrinkles?). Overall though, for all the things humans can do, we need a "big" brain.

About brains being "sexy". Well, the guy with more intelligence will have more to provide a mate as far as food, shelter, etc. That would be appealing. His children would then survive better, and that would leave those smart people around while the dumb ones perish. A smart female might have more young survive since she would better care for her children.

Factor in all other things we find "sexy" as far as body shape, facial features, etc. and we get a variety of folks walking the planet. A certain degree of intelligence does help though. You'll notice not so intelligent people don't take as good care of themselves and get more and more unattractive past their childhood years. Without brains to overcome any other unattractiveness that isn't a result of being less intelligent (bad teeth, whatever), well then their chances of reproducing does start to become less likely. I can overlook bad teeth or something if the guy is smart and helps out in "providing".

Without a certain degree of intelligence (and a brain big enough to allow for this intelligence) compared to the rest of the population then your chances of surviving drops. Without a certain degree of fitness or "attractiveness" your chances of reproducing is less. I think you have a few factors to assess in human survivorship or whatever.

[Xeriar]

Originally posted by Yahweh
I thought our brains have become smaller than our previous ancestors. As long as intelligence isnt related to big brains, then you can safely assume that a smaller brain would equate to more efficient usage.

Neanderthals had bigger brains, but they also had larger bodies.

[CurtC]

But Neandertals weren't our ancestors.

I think the answer is that large brain size is necessary for higher intelligence, but there are factors that affect that, such as how it's wired, which in humans confounds the size metric. However, as a species, humans are much more intelligent (at least linguistically) than other animals, and our brains are quite a bit bigger. I don't think there's any doubt that our greater intelligence depends on a generally larger brain.

If your friend asks why other animals don't evolve intelligence to help them survive, the answer is that this large brain is extremely costly. Humans just happened to inhabit a niche where it would be an overall benefit. And from what I've heard about how the human population had a bottleneck, that we all came from a handful of individuals, we almost didn't make it.

[Soapy Sam]

Other animals did evolve intelligence.
Most mammals have bigger brains than they "need" for their body mass and complexity.

Within mammals, primates have a particularly large excess brain capacity.

Within primates, apes excel in that regard.

Within apes, the superstar is man.

And octopuses are a darn sight smarter than you would expect.
And anyone who thinks birds are stupid just hasn't been paying attention.

And the struthiomimids were getting well up in the brain mass to body mass ratio, when fate dropped a large rock on them. Which is probably just as well from our point of view.

Intelligence is everywhere.

[Asolepius]

Originally posted by Soapy Sam

Intelligence is everywhere.
Good point - intelligence is not a dichotomous property, but a continuum. Re: birds, I read not long ago about a parrot with a human mental age of 4. It could count single digits, and put them into sentences. Unlike chimps, it could actually say them!

[Pragmatist]

Originally posted by Xeriar
Neanderthals had bigger brains, but they also had larger bodies.

Did they? I thought the average Neandertal was about 4'11" tall?

I also seem to recall hearing recently about a discovery that modern humans have a genetic sequence that is only otherwise present in Neandertals, which implied that although they are not our primary ancestors, that there is some "Neandertal blood" in modern humans. But I might be mistaken about that, I wasn't paying much attention at the time and may have misinterpreted something.