Nature and Nurture Influence I.Q.

NEW YORK (Reuters Health) - Hoping to resolve the question of where intelligence comes from, researchers now suggest that a person's intelligence quotient, or IQ, is the outcome of a continuous circle of influence involving both genes and environment--and that the measure is fluid over a lifetime.

``Even though a whole lot of traits--including IQ--have been shown to be highly heritable, much of the effect of genes may come from the way genes seek out good environments,'' said study lead author William T. Dickens of the Brookings Institution in Washington, DC.

Dickens and his colleague James R. Flynn of the University of Otago in New Zealand developed a new mathematical model to unravel the complexity of the nature-nurture interaction. Reporting in the April issue of Psychological Review, the researchers note that a relatively small change in the environment can have a very large and quick impact on IQ, but that such impacts may prove to be short-lasting.

In this regard, Dickens and Flynn stressed that those who attempt to manipulate the cycle by adjusting the environment will find the process tricky and elusive. They noted, for example, that parents who place a child in a challenging pre-kindergarten setting may indeed observe a fast rise in their child's IQ. However, they will just as often find that the child's gains are lost once he or she leaves the environment, if the one that replaces it is less demanding and supportive.

Nevertheless, Dickens and Flynn found that seemingly small environmental triggers play a large--if changing--role in influencing an individual's IQ. In what the researchers suggest is a snowball effect, a person who is perhaps only slightly more genetically ``gifted'' than average may have easier access to social and work situations that involve higher-than-average degrees of intellectual stimulation.

This person will then be motivated to seek out more of the same, they noted. He or she will perhaps set a higher bar for educational and job-related pursuits, which will put them in contact with like-minded people. And the result, according to the researchers, is an upward spiral of IQ that is driven by both genes and circumstance.

``The implication is that if you have a small genetic difference between two people, it can be blown up by this process,'' Dickens told Reuters Health. ``A small initial advantage in something like IQ leads to an environment that benefits that trait, which leads to a better IQ, which leads to a better environment and so on.''

Dickens emphasized, however, that the role of environment can and does shrink as a person ages--with their genetic predisposition taking greater prominence as individuals move outside the more controlled environment of their early years and into a setting of their own choosing and interests. As proof of this development, he and his colleague point to the experience of adopted siblings who have different biological parents. They noted that as they age and leave home, such siblings' IQs often differentiate and more closely resemble their genetic roots.

SOURCE: Psychological Review 2001;2:1-

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