Parents want their newborns to have big heads — not so much at birth, but shortly thereafter. Big heads imply intelligence, growth, and good genes. Well, so it’s presumed anyway. So, when my son’s first checkup revealed that his head circumference was solidly 50th percentile, I was shaken. Our pediatrician, unable to console me, resolved to never again show me raw growth data.
“Some dads,” she told me. “Shouldn’t see the percentiles.”
She was right, of course. Head circumference has essentially nothing to do with intelligence and, as long as your child’s head is average-size and regularly growing, there’s no cause for alarm when he or she comes in a bit behind the curve. Still, a handful of preliminary studies have suggested links between brain size, head size, and intelligence. That research can’t necessarily be dismissed out of hand so it’s hard to figure whether or not dome size matters — especially with all that percentile data clouding the picture.
Our obsession with head size goes back to phrenology, a discredited (and super racist) pseudoscience that proposed to determine intelligence and personality type by measuring skull size and shape. The science fell out of favor some time ago, but some of the premises upon which it was built have hung on even though efforts to link intelligence to brain weight have been fruitless. Albert Einstein’s brain was, for instance, of only average weight (about 3 pounds). The author Jonathan Swift’s brain weighed a more exciting 4.4 pounds, but, alas, the Nobel laureate Anatole France had a brain that weighed barely 2 pounds.
Doctors know all this — not the Anatole France stuff, the brain weight stuff — so it’s not intelligence they’re after when they measure your newborn’s head circumference. In most cases, doctors track infant head growth because deviations from the expected growth curve often are the earliest signs that something is wrong with the brain. It’s less about the head size itself than about measuring consistent, predictable changes in size.
At the height of the Zika epidemic, doctors measured head size to rule out microcephaly, a debilitating birth defect sometimes caused by the virus. When Charlie Gard’s parents argued that their son, despite his terrible illness, still might survive if given experimental therapy, one of the key questions in the ensuing court case was whether his head had grown in the past three months.
On the other hand, preliminary studies have shown that 1-year-olds with larger heads score higher on IQ tests later in life. And bigger heads do tend to hold bigger brains. “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,” Grant Hulbert, a biology professor at California State University once told the American Academy for the Advancement of Science.
The question is whether brain size — or even IQ, when it comes down to it — really matters. Studies have cast significant doubt on the notion that IQ tests accurately measure intelligence. And how we should measure brain size is part of a dizzying debate among neuroscientists. Whale and elephants have larger brains than humans, but that’s probably just because they’re a lot bigger than we are. Still, some neuroscientists now rely on a figure known as the encephalization quotient, which uses forgiving math to help human brains rule the animal kingdom — at least by a metric we invented. Meanwhile, most MRI studies report only weak correlations between brain volume and intelligence — most of which can be explained by yet another weak correlation between height and intelligence. Tall people, it seems, are a bit smarter and have slightly larger brains to boot.
In sum, the science doesn’t suggest that intelligence has much to do with head or brain size. And when doctors measure your kid’s head, they’re mainly trying to figure out whether he or she is growing normally, not passing judgment on his or her IQ. Besides, Einstein’s head — languishing right around the 50th percentile — didn’t seem to have any trouble describing relativity.
My kid and his average head will be just fine. Betting yours will, too.