John Hewitt is a neuroscientist who studies the biology of intelligence. He's also a parent. Over the years, Hewitt has periodically drawn upon his scientific knowledge in making parenting decisions.
"I'm a father of four children myself and I never worried too much about the environments that I was providing for my children because I thought, well, it would all work out in the end anyway — aren't the genes especially powerful?" Hewitt says.
Intelligence has a strong biological component, Hewitt knew. If your parents are smart, you'll probably be smart — even without a lot of fuss about the right schools and learning environments.
But recently, Hewitt discovered something that surprised him.
"Well, I may have been wrong," he admits. "It may well be that the environmental boost you can get, or the detriment you can suffer through adversity, may indeed be a little more important at a critical period in adolescence than I had previously thought. And this may especially be true for parents of very bright children."
What Hewitt, director of the Institute for Behavioral Genetics at the University of Colorado, is talking about is a new understanding of the interplay between your genetic inheritance and how you learn from the environment. He credits another researcher, Angela Brant, for coming up with a new insight into this critical period in development.
To understand what Brant found, here's some context: Both children and adults learn things, but children are better than adults at some kinds of learning. Think about trying to learn a new language.
"In language you have specific words and vocabulary," says Brant, a postdoctoral fellow in psychology at Penn State University. "And you also have the broad patterns of the language — the syntax. We know that adults can pick up vocabulary words, but they are less able to pick up syntax."
So what is it about children that allows them to grasp the "deep" knowledge of syntax more quickly than do adults? Neuroscientists think the reason children do better at such challenges is that young brains are more receptive to learning.
"Until adolescence there are lots of new connections being made between neurons to store patterns and information collected from the environment," Brant says.
In childhood, the brain adds many synapses in the cortex. This comes at a time when the brain is especially responsive to learning. This is typically followed by cortical pruning in adolescence, as the brain shifts from hyper-learning-mode.
Hewitt agrees: "The developing brain is a much more flexible organ than the mature brain."
Learning doesn't stop at adolescence, of course, but the "sensitive period" – where the brain is hyper learning mode — does appear to come to an end. Learning new things gets harder.
At least that's the typical pattern. But Brant and Hewitt find that for some children, there is an extended learning period. Among some children with very high IQ, the brain appears to stay in learning hyperdrive for an extended period.
Brant, Hewitt and other researchers recently tracked a group of children over time. Some were genetically identical twins, some were fraternal twins, some were non-twin biological siblings, some were adopted siblings.
Using mathematical techniques that allow researchers to disentangle the effects of genetic and environmental influences on individuals, Brant noticed that kids who had higher IQs to begin with seemed to have an extended period in adolescence during which they retained the ability to learn at a rapid pace, just like much younger children.
"I found that twins that had a higher IQ were showing a more childlike pattern of influence during adolescence," Brant says.
Hewitt agrees. "It was as if there was an extended sensitive period in the higher IQ individuals. Or another way of looking at it is the sensitivity to the environment which is characteristic of earlier childhood seemed to end earlier for individuals with lower IQ."
Hewitt and Brant don't know why some teenagers continue to learn at the pace of much younger children. It may be that smart kids gravitate to challenging activities and this keeps them receptive to learning. Or it could be that genes that lead to high IQ also trigger an extended learning period.
Hewitt points out that an extended learning period does not necessarily mean a further increase in IQ. But a very smart teenager with an extended "sensitive period" of learning might be able to pick up a new language or a musical instrument. Such learning can have long term benefits, Hewitt explains, even if the teenager has the same IQ before and after she learns the language or the instrument.
"Even if in the end the IQ ends up being determined to a large extent by the genes, if there's been a period where the environment makes a difference, that could have lifelong consequences," Hewitt said.
The study, published in Psychological Science, suggests that for many children it may be a mistake to stop learning new things. Even if you're a teenager, it might not be too late to start Chinese, chess or the cello.