Thanks to all for your thoughts and paper recommendations. I realised that the questions in my initial email should have been not about absolute brain size but, of course, about the brain-to-body ratio expressed in weight or volume. I guess, then, that from the graph Matt pointed to, the more intelligent species can be interpreted to be those that deviate the most (upwards) from the expected proportionality between body and brain weight (the solid line).

Applying this reasoning to gender differences within humans, would it be correct to say that, if men and women are assumed to be equally intelligent, this reflects that their brain/body weight ratios are roughly equal?


On 10 July 2014 20:56, Brandenburg, M.N. <[log in to unmask]> wrote:
Hi all,

I am not an expert in intelligence, but I do specialize in social behavior and it has been argued that our brains are so big because of the social demands associated with 'being human'  (as opposed to being a primate or elephant).

This paper discusses the correlation between the size of the social group of certain species and the relative volume of the neocortex: http://www.ncbi.nlm.nih.gov/pubmed/12612630

Intuitively, I'm inclined to oppose the idea that brain size and intelligence are linearly related. Maybe on a group level, but with all the individual variability and environmental factors in play, I think it may be a rather dangerous claim to make.

Best wishes,
Marcia
From: FSL - FMRIB's Software Library [[log in to unmask]] on behalf of Matt Glasser [[log in to unmask]]
Sent: Thursday, July 10, 2014 9:35 PM

To: [log in to unmask]
Subject: Re: [FSL] Brain size and intelligence

It might, as exercise is supposed to improve cognitive function, though perhaps not because you improve your position on the curve. :)

Matt.

From: Jesper Andersson <[log in to unmask]>
Reply-To: FSL - FMRIB's Software Library <[log in to unmask]>
Date: Thursday, July 10, 2014 at 2:25 PM
To: <[log in to unmask]>
Subject: Re: [FSL] Brain size and intelligence

So,

if I loose 5 pounds, will that make me smarter? I better start exercising.

Jesper

On 10 Jul 2014, at 20:20, Matt Glasser <[log in to unmask]> wrote:

I thought elephants were fairly smart mammals, no?  In any case, I believe brain size is usually scaled with body size and the excess brain size over body size is associated with more intelligence:


Peace,

Matt.

From: Francesco Puccettone <[log in to unmask]>
Reply-To: FSL - FMRIB's Software Library <[log in to unmask]>
Date: Thursday, July 10, 2014 at 1:34 PM
To: <[log in to unmask]>
Subject: [FSL] Brain size and intelligence

Dear FSL list,

Apologies for this being off-topic (not related to the FSL software) but I'm hoping that someone can kindly suggest a review paper (or explain in their own words) the theoretical principle by virtue of which brain size and intelligence are not linearly related. I could not find a satisfactory answer from the literature I read.

As far as I can see, a proportionality does seem to exist at some level between total brain size (or total gray matter volume) and intelligence, exemplified by the rather monotonical relative relationships between those two factors among the different primates, where humans have the largest brains. Also, I seem to recall studies showing such a dependence within humans as well, with intelligence being measured as various metrics of general cognitive ability (e.g. IQ, g factor etc).

However, clearly, within the animal kingdom, the largest creatures aren't necessarily the ones showing the clearest evidence of intelligence (take for instance the elephant vs the small but rather clever crow). Equally, among humans, the fact that females have, on average, smaller brains doesn't make them less intelligent (if measures of intelligence are unbiased and well chosen), just as people with bigger heads (and brains, assuming proportionality) aren't necessarily more intelligent.

Basically, if brain size is so often invoked as the reason why humans are more cognitively capable than other great apes, then why doesn't the same argument (whatever its physiological justification may be) hold also for male vs female humans, or elephants vs mice?

I know this is a very complex topic, but a simplified explanation of this apparent paradox, and maybe a good review recommendation, would be really helpful; thanks a lot !

--Francesco