Then, in 1987, Flynn showed that in nation after nation, the current generation outscores the last generation by some 9 to 20 IQ points. The gains are greatest on those tests often called the best measures of intelligence. Their size and speed dictate an environmental explanation. Flynn applied Jensen's model. An environmental explanation meant putting the current generation within the top one-tenth of one percent of the last generation in terms of environmental quality. What was known to be true was shown to be impossible.
How could solid evidence show both that environment was so feeble (kinship studies) and yet so potent (IQ gains over time)?
This is hot off the presses -- and is undoubtedly the most brilliant explanation of intelligence research I've ever seen. (The relevant chapter in Genome is the second best, hitting as it does everything except the theory that happened after its publication!)