Will we run out of brain space?

Nineteenth century scientists liked to measure skull cavities to determine brain size. They thought that the bigger the brain, the smarter the individual.

We know now that theirs was a naive and inaccurate way to measure intelligence — whatever that is — but there does seem to be a physical limit, in practical if not absolute terms, to how much larger the human brain can become.

Is there a functional limit to our intelligence, too? Not necessarily, according to Douglas Fox in “The Limits to Intelligence,” in Scientific American (July 2011).

The brain size question seems relevant, considering that the brains of human infants expand in size much more rapidly during growth than do the brains of young chimpanzees, our closest primate relatives. According to the journal Current Biology, as reported by Sindra N. Bahnoo in New Scientist (August 12, 2011). Japanese researchers report that “the white matter in the prefrontal cortex of chimpanzees does not grow as rapidly as it does in humans.” The researchers speculate that greater brain growth may contribute to human superiority in communication and social interaction skills.

Why wouldn’t growing more and more brain cells (and increasing the speed with which they communicate, to counter the slowing effects of greater signal distances) just keep making us more and more intelligent? Fox writes that ” such tweaks would soon run into physical limits. Ultimately those limits trace back to the very nature of neurons and the statistically noisy chemical exchanges by which they communicate.”

A larger brain can have more neurons, which should enable its complexity to grow as well. But, Fox reminds us:

Brain size alone did not determine intelligence: a cow carries a brain well over 100 times larger than a mouse’s, but the cow isn’t any smarter. Instead brains seem to expand with body size to carry out more trivial functions: bigger bodies might, for example, impose a larger workload of neural housekeeping chores unrelated to intelligence, such as monitoring more tactile nerves, processing signals from larger retinas and controlling more muscle fibers.

Fox quotes Vijay Balasubramanian, a Penn physicist, who believes that “it is very likely that there is a law of diminishing returns” with increasing brain size, thanks to the dramatically greater energy drain imposed by a larger brain. Our current brains already consume 20% of the body’s energy, and a larger brain would require even more of our resources.

A larger brain not only consumes more energy; it also slows down, as the distances between any particular pair of neurons increases. It’s sort of like the expanding universe, in which we keep getting further away from the “edges” even as we “stand still.” Our brains already deal with this problem, solving it partly by dividing functions into specific geographic regions of one or the other hemisphere.

How about more neurons, but smaller? That’s fine, but only up to a point. The proteins that produce the chemical messages by which the brain works become more and more unstable as they are packed closer and closer together. Eventually, they lose their functionality — the ability to “switch” on and off — and the whole communication grid collapses into chaos.

So it seems that we’re stuck, that we’re not going to end up with those super-domed foreheads so popular in 50’s sci-fi movies like This Island Earth (the source of this article’s opening illustration). Does this also mean that we can’t get any smarter?

Not necessarily. As Fox notes, two effective strategies for increasing our intellectual capacity already exist, and they have been in use for thousands of years.

The first is the older tactic, and it’s been in our survival arsenal since the beginning:

The human mind … may have better ways of expanding without the need for further biological evolution. After all, honeybees and other social insects do it: acting in concert with their hive sisters, they form a collective entity that is smarter than the sum of its parts. Through social interaction we, too, have learned to pool our intelligence with others.

I don’t have to know everything, or be able to do everything — not as long as you know and can do what I don’t and can’t, and I do the same for you. The practical application of this tactic lies behind the reality that if there’s a blacksmith and a tailor and a seamstress in the group, you don’t need to learn these skills. Maybe your contribution is to have memorized the group’s oral history; maybe mine is to know how to make the lovely mead that everyone enjoys in cold winters.

Then there is technology. From the first scratched clay tablets to illuminated manuscripts to printed books to this computer, we have steadily improved our ability to “assign” greater and greater volumes of information to storage devices outside our own brains, freeing up some of our valuable cognitive real estate.

Fox speculates that with the Internet we may have solved our brain-size problem, making us smarter in practical terms while removing the evolutionary incentive for getting smarter physically:

One could argue that the Internet is the ultimate consequence of this trend toward outward expansion of intelligence beyond our body. In a sense, it could be true, as some say, that the Internet makes you stupid: collective human intelligence—culture and computers—may have reduced the impetus for evolving greater individual smarts.

This way of looking at the brain not as a metaphysical entity but rather as a physical holder of information — not just sensory inputs but also memories, facts, skills and the rest — is relatively new. Books like Gleick’s The Information, reviewed here recently, make it clear that it’s a very useful construct.

So if you’re worried that the Internet is making you stupid, take some comfort from the possibility that it doesn’t matter, as long as the Internet itself keeps getting “smarter.”