This article is also about how intelligence changes over time but looks at the role of genetics.
http://online.wsj.com/article/SB10001424052970204555904577168973230172642.htmlNew Insight Into Aging Brains:
Study Links 24% of Intelligence Changes Over a Person's Life to Genetic Factors
Wall Street Journal
JANUARY 19, 2012
By GAUTAM NAIK
Nearly a quarter of the changes often seen in a person's intelligence level over the course of a lifetime may be due to genes, a proportion never before estimated, new research shows.
The study suggests that genes may partly explain why some people's brains age better than others, even though environmental factors likely play a greater role over a lifetime.
Understanding the factors behind healthy mental aging has become an increasingly vital one for societies with large elderly populations. However, it isn't an easy task.
Traditional methods of estimating the influence of genes and the environment on intelligence have largely been limited to comparisons between people who are related, such as identical or fraternal twins. The shortcoming of such studies is they didn't clearly apportion the effects of each factor on intelligence.
Modern DNA-based techniques are now helping to refine the search.
The new study, published in the journal Nature, offers one of the first estimates of how much genes and the environment contribute to fluctuations in a person's intelligence between adolescence and old age. It found that genetic differences account for 24% of the variation.
However, the paper didn't identify any of the myriad genes or environmental factors that might be involved.
"The nature-nurture controversy is never more contentious than when it concerns the genetics of intelligence," wrote Robert Plomin, a psychologist at King's College in London, in a commentary accompanying the study, in which Dr. Plomin wasn't involved.
The Nature paper, he said, "may mark the beginning of the end of this controversy" because it relies on DNA data from unrelated people, which is harder to dispute.
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ETA: I think the paper is
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10781.html"Genetic contributions to stability and change in intelligence from childhood to old age" by Deary et al.
