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Does Brain Size Affect Intelligence?

By Jacob Queen
Updated Feb 23, 2024
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The question of whether brain size affects intelligence is heavily debated in science, and there is no certainty on the issue. There is evidence to suggest that brain size can make a difference, but there is also evidence suggesting that it isn’t the most important factor. According to some experts, brain size seems to be more important to some kinds of intelligence than others. There are studies in the animal kingdom that have also shown large contradictions regarding brain size and intelligence among different species, and this has generally made scientists more uncertain about the issue.

Animals that have made scientists most uncertain are birds. Many bird species, especially those in the crow family, show very complicated social behaviors and demonstrate the ability for complex reasoning. They are generally able to do this despite the fact that their brains are smaller than many species with less formidable cognitive abilities. Some experts think this is because birds have particularly complex neuron structures that allow their brains to be more efficient.

There are also other studies that show a strong direct relation between brain size and intelligence. These studies have examined intelligence tests across a wide array of species and have focused on a more general type of problem-solving ability. The reason for these results is disputed. Some experts think that simply being larger physically causes the animals to require more intelligence for some reason, while others think that brain size is the primary factor.

In people, studies of brain size and intelligence have also been relatively contradictory. For example, most men have larger brains than most women, but studies have been unable to find statistically significant differences in intelligence between men and women. There are many cases where people with much smaller brains have been able to demonstrate much more mental capacity than people with larger brains. It is generally true that brain size and body size are usually proportionally-related among humans, but intelligence and body size are often totally unrelated.

Some experts think that the structure of the brain, or maybe the specific size of certain parts of the brain, have more to do with intelligence. There is also evidence that brain size changes based on a person’s experience, and as people gain more mental knowledge, their brains may actually grow. There is a lot of evidence to suggest this happens during the childhood years when people are developing, but there is also some evidence showing that it happens after people reach adulthood as well.

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Discussion Comments
By irontoenail — On May 27, 2012

@browncoat - If you're thinking of that whole "we only use 10% of our brains" saying, it's actually a myth. We use most of our brains, although not all at once.

But, then there was a case where a man was managing to function, to have a normal life with only about 20% of his brain still alive and working.

Frankly, the brain is still quite a mystery to scientists. They just don't completely understand the way it works. Sometimes it can cope with damage and sometimes it can't. Sometimes size makes a difference and sometimes it doesn't.

By browncoat — On May 26, 2012
@umbra21 - Well, that would be interesting but I don't think I'd like to be the person who sat around and did nothing but memorize things.

I suspect, anyway, that the human brain is only capable of memorizing so much. I mean, I think it can memorize a tremendous amount, but I don't think that amount is endless.

I do wonder if the size of the brain is related to that though. Maybe people with bigger brains simply have slightly more storage capacity. I don't think that we really use enough of our brains for the size of them to have all that much difference. I mean, there isn't all that much difference between the largest human brain and the smallest (average) human brain.

Certainly not enough to make a difference when we don't use all of our brains in the first place.

By umbra21 — On May 26, 2012
I did read once that there is a measurable difference in the weight of the brain before you become a London taxi driver and after you do.

In order to become a taxi driver in London you have to pass a really difficult test, where you basically need to memorize most of the street names in London.

As you can imagine, there are quite a few of them and it takes a long, long time to memorize them all, and where they are on the map. Actually, I think it might be that each taxi driver has to memorize only certain parts of the city.At any rate, it's a huge task and a lot to remember and people who manage to pass the test and become taxi drivers have managed a real feat of memorization. And scans have shown that this feat actually leaves a measurable mark on the human brain size.

I suppose it must be from all the new connections that must be made in order to process all that information.

It makes me wonder how big a brain could potentially get if someone just sat around and memorized stuff for years and years.

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