In the biggest study to date examining the influence of birth weight on intelligence, scientists writing in the British Medical Journal have found that babies born on the heavy side of normal tend to be brighter as adults. Experts have long known that premature or underweight babies tend to be less intelligent as children. Scientists think it has something to do with bigger babies having bigger brains, or perhaps with having more connections within their brains.
Birth weight is only one of numerous factors that influence cognitive function.
Similarly, Richards said, the head start enjoyed by hefty babies can be squandered. Living in an overcrowded home, breathing polluted air, or being caught in the middle of a divorce tend to diminish children's intelligence scores, he said. The scientists found that birth size influenced intelligence until about the age of 26. After that, it tended to even out, as other factors began to play a more important role. And of course, there are always exceptions.