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From: green_knight@greenknight.org.uk.invalid
Gerry Quinn wrote:
> green_knight@greenknight.org.uk.invalid says...
> No, it's the old 'correlation is not causation' thing. Statistics
> (though here we are really talking about measurement and observation,
> rather than statistics as such) cannot prove anything. But we should
> take account of it, no? We combine it with reasoning, which tells us
> that the stork correlation is irrelevant and the brain size correlation
> is not.
If you start from the stork premise, then the data proves your
assumptions. If you start from the 'size matters' premise, then your
data proves your assumptions. Same mechanism.
The difference is that for the first, we have proven alternative
explanations which are a lot more plausible.
For the second, on the other hand, we have a premise that has - as far
as I can see - no biological mechanism.
> The following is a bit of reasoning, for example:
>
> > > One assumes large brains evolved for a purpose. Brains are expensive to
> > > run and don't appear to be useful as nutrient stores. The heat they
> > > generate is largely wasted due to their position in the body.
> > >
> > > Why do YOU think humans might have evolved relatively large brains? Can
> > > you think of plausible reasons not to do with intelligence?
> >
> > I think that what humanity _as a species_ did has little or no relation
> > to brain size in individual humans.
>
> I'll take that as assent that we did in fact evolve larger brains
> because of the benefits of the greater intelligence they provide.
Don't, because I did not say that. I think there's a high likelyhood
that, speaking on an evolutionary scale, the larger brains went along
with positive traits. This is not necessarily a causal relationship.
> But why do you think the effect switches off when it comes to individual
> humans?
Because I don't believe that it exists in the form you postulate,
because there appears to be absolutely *no* correlation in the data I
have been able to observe, and there is - as I have quoted - strong
evidence to disprove it.
> You do know that, at least in some very strong senses, natural
> selection operates at the individual level? [I have no problems with
> the concept of group selection, incidentally - just pointing out that
> reproductive success in humans does have much of its operation at a
> micro level.]
There appears to be absolutely no selection for large-headedness, or
evidence that humanity is getting collectively larger-headed.
> > I do not for one moment believe that humans are any different from other
> > mammals, and I am not aware of anyone claiming a Newfoundland is more
> > intelligent than a Yorkshire terrrier, for all that their brain sizes
> > differ greatly.
>
> I am aware that people say different breeds of dogs differ in
> intelligence. I don't know much about the two breeds in question,
> although I think you would have to correct for body size before
> discussing relative brain size of a large and a small breed.
That's a whole different kettle of fish - if absolute size of the brain
does not matter, but size _relative_to_the_body, you're argueing a
different theory.
> There are probably also differences due to the nature and strength of
> selection pressures on dog breeds.
Of course there are. And they're breeding for different _types_ of
intelligence, too, but large brain size - or even large-in-relation
brain size does not come into it. Otherwise - given the relatively short
generation sequence - we would be seeing a lot more large-headed dogs.
> > In individual humans, intelligence is a factor not of brain mass, but of
> > connections within the brain, about which we are learning more and more
> > as time goes on - you can have a size XL brain, but if you don't use it,
> > it won't be much use to you. If you *do* use it, and form new
> > connections, and keep feeding it new information, and train it, you will
> > be 'more intelligent' in any number of measures, but your brain will
> > still be the same size.
>
> That may be true (although you have not shown that the ability to form
> connections, or indeed the number of connections formed, does not
> correlate to brain size).
I have. You may have missed the point about Hydrocephalus, but there it
was: drastically reduced brain mass, normal intelligence.
> Why didn't proto-humans just grow more connections, if this is possible
> without a brain size increase?
Maybe - quite likely - you need a certain amount of brain in the form of
more-than-minimum rather than more-is-better; if you have no muscles you
are weak, if you develop muscles you are getting stronger, but you can
develop muscles long past the point where they are functional - see body
builders. Or maybe the increase went along with an increased development
of brain regions, or ability-to-form-connections. The human body
contains a number of 'will do' solutions - as long as the cost is not
too high, we're not punished for them.
> But certainly, intelligence is not direcly proportional to brain mass as
> a rule, any more than athlethic skills are proportional to muscle mass.
> That is not to say they have no correlation.
The problem is that this correlation is trotted out time and time again
as something that is proven, rather than a rather shaky and not overly
useful hypothesis when studying human intelligence.
Catja
--
writing blog @ http://beyond-elechan.livejournal.com
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