Big Heads

Big Heads Photo Credit: Clipart.com.

If somebody is really smart, other people might say: "She's got a really big brain." But when it comes to brains, does size really matter? In this Science Update, you'll hear the complicated answer to that simple question.


Are big heads better? I'm Bob Hirshon and this is Science Update.

There are many ways to assess a person's intelligence. But Ed Klaber of Chelmsford, England, came up with one of his own. He wants to know if people with bigger heads have bigger brains.

We asked Grant Hurlburt, a visiting professor of biology at California State University in Bakersfield. He says measuring the size of the head does give some indication of how big the brain is.


Even though head size also depends on factors such as the muscularity of the head and thickness of the bone, it's very likely that a bigger head means a bigger brain.

But Hurlburt says people with bigger brains aren't necessarily smarter than those with smaller ones. Studies have shown a weak correlation between brain size and I.Q. But scientists aren't sure what causes it.


We're still trying to investigate, you know, what it is about the brain that correlates with I.Q. And what kind of information processing goes on. Brains are very complicated, and we're still working on them.

So, many other factors besides having a big head ultimately determine a person's braininess.

If you've got a science question in your brain, call us at 1-800-WHY-ISIT. If we use your question on the show, you'll get a free Science Update mug. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

The main question at hand is whether smarter people have bigger brains. As is the case with many science questions, the answer to this one isn't "yes" or "no" but "kinda," "sometimes," or "not necessarily." As you heard, you can't always tell how big someone's brain is from the size of their head—but the two sizes are somewhat related. The same is true with brain size and intelligence.

The most we can say about brain size and intelligence is that by and large, all other things being equal, people who have larger brains tend to have slightly higher I.Q.'s than people with smaller brains. (I.Q. stands for intelligence quotient; it's a standard measure of intellectual ability.) But a lot of things have to be taken into account. For example, when you compare brain size, you really have to compare brain size relative to body mass. It's not reasonable to expect a 5'1", 100-pound woman to have the same size brain as a 6'6", 280-pound man. You have to ask the question: Is this person's brain larger or smaller than you might expect, given his or her body mass?

Even then, the relationship between brain size and intelligence is pretty weak, and there are lots of exceptions. Anatole France, a French author, had one of the tiniest "normal" brains on record, but he was certainly no dummy. On the other extreme, Jonathan Swift (the author of Gulliver's Travels) had a big honkin' brain, at the top end of all the brains ever measured (though still only twice the size of Anatole France's). Does that mean Swift was the smartest man who ever lived? He was certainly a bright guy, but it's hard to get behind any statement so extreme.

Still, it's hard to dismiss brain size entirely. The weak relationship between brain size and intelligence that shows up within the human population is somewhat more striking across the animal kingdom. Compared to other animals, humans have enormous brains compared to our body size (triple what you would expect in an average animal). Dolphins, other primates, and small whales also have big brains, and they're all pretty smart too. Within birds, parrots have big relative brain sizes, and chickens have tiny ones. And based on lab studies of learning and thinking, parrots are geniuses compared to chickens.

Overall, though, many factors besides mere size probably contribute to how well a brain functions, including the way it's organized, how many nerve cells are packed in per square inch, the quality of nutrition and environmental stimulation that you get while your brain is developing, and a host of other issues. Also, don't forget that these studies measure intelligence in terms of I.Q. score—a useful scale, but not necessarily the final word on how smart someone is. Many successful, shrewd, creative, and intelligent people have only average I.Q.'s, while many people with high I.Q.'s are underachievers.

Now try and answer these questions:

  1. What evidence supports the idea that brain size is related to intelligence?
  2. What evidence suggests that brain size alone is not enough to predict intelligence?
  3. How do you reconcile these contrasting bodies of evidence?
  4. Suppose you wanted to find out if people with big noses had a better sense of smell than people with small noses. How would you test this idea? Give an example of an experiment you might conduct. Be specific about how you would measure nose size and smelling ability.

For Educators

"My Brain is Bigger than Your Brain" gives a short overview of brain and body size in the animal kingdom.

Atlas of Human Anatomy in Cross Section features online dissections of the human brain and nervous system.

The Human Brain is an online exhibit from Philadelphia's Franklin Institute.

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