Imagine you measure both the bodies and brains of all the primates on Earth bar humans: beasties like bonobos, chimps and gorillas. Then, using this ratio and based on the average human's size, you estimate how big our brains should be.
To check your estimate you decide to open up your friend's head to take a peek inside. When you do, you're mighty surprised to find a brain about three times larger than you were expecting. "Aha," you say, "This is where our amazing capacity for language, emotion, social organisation and creativity comes from."
This argument soon breaks down when you try chatting to an elephant.Naturally, then, it's an attractive idea that the bigger the brain, the more able the animal. This argument soon breaks down, though, when you try chatting to an elephant - an animal with a brain three times the size of ours. OK, you might say, it doesn't work across species, but maybe it works within species.
Well, now trouble is not far away, and here's two reasons why:
1. Men's brains are generally bigger than women's, on average by 100 grams (say about 7% bigger).
2. Different races have different head sizes with Asian children averaging the largest at birth followed by White children, leaving Black babies with the smallest heads.
So you see the kind of dangerous, shark-infested waters we're now swimming in? This is no longer just science, it's political; with claims to the answer potentially being seen as both sexist and racist.
This is why I'm more than a little relieved to report the view of neuroscientist Dr David P. Carey who has reviewed the research in this area and finds little evidence for the claim that bigger brains mean greater abilities (Carey, 2007). He argues that the evidence from neuroimaging, behavioural genetics and comparative cognition is largely unconvincing:
"I have little confidence that looking at a sophisticated twenty-first century brain scan (in any number of impossibly sophisticated ways) of a collaborator, competitor or any old conspecific [other human] is going to tell me anything meaningful at all about their capabilities to perform in any cognitive way, psychometric or not." (Carey, 2007, p. 119).
Intelligence sceptics
A second layer of scepticism about the brain size/intelligence connection is captured by an old joke that goes like this:
Q: What is intelligence?
A: Whatever intelligence tests measure.
The joke expresses a scepticism many harbour towards measures of intelligence. Does intelligence really tell us anything useful about a person, or does it just tell us how good they are at taking intelligence tests?
The jury is very much out on this point. The originators and manufacturers of intelligence tests will tell you they are good predictors of people's real-world performance, while many others are not so sure. In fact, you'll likely hear equally strong answers from equally well-qualified people that are completely contradictory.
It's not how big it is...
The default position should be a high level of scepticism about any claims for a relationship between brain size and ability. This is because:
1. The connection between brain size and intelligence is largely unproven, and;
2. The relationship between measures of intelligence and real-world functioning and behaviour is highly contentious.
So, there you have, confirmation of the oldest defence in the book: it's not how big it is, it's what you do with it.
