I haven't read the books you've mentioned, although I'm pretty familiar with the debate, and the latest arguments.
I think it's interesting to make an analogy with a sport like running. If you measure running ability in a group where every person has absolutely no training, all the differential in running ability will be genetic. But a person will be able to train and improve, and so a change in environment ran result in gains in ability. If some people in the group start to train harder, then the differential in scores will be a mix of environmental and genetic.
If you compare members of a cross country team who all endure the same grueling training, the differences in their running speeds will be genetic. If one member tries to train even harder, he will probably be unable to raise his speed even higher. At some point, he maxes out and no training will raise his speed even further.
The subtests that have a flat trend were vocab, math, and general knowledge. What this indicates is that the environment of a century ago maxed people out at these skills a century ago. This is not surprising, as these skills are the most culturally common skills. Even in 1900 a person had constant exposure to reading, math, and general knowledge.
The subtests that have seen the greatest rise are all obscure skills - object assembly, picture arrangement, similarities. My guess is that the great increase in schooling resulted in more training in these obscure skills. Increased availability of games and puzzle books also helped. In 1900 if you were a genius kid, you read the classics. In 2009 you can play all sorts of fun puzzle games online or in books. As a result of this, scores on these obscure puzzles have gone up.
The net of this may mean that the hardcore hereditarians ( Murray, Jensen) are wrong about the specifics but right about the big picture. They are wrong to think that differences in the Raven test by themselves mean that one group has more natural cognitive abilities than another group. But they are probably right that individual and group differences in the economically and socially useful cognitive skills are mostly genetic. The differences in the obscure cognitive skills ( Raven's, picture arrangement) may be much more environmental.
Comments
I haven't read the books you've mentioned, although I'm pretty familiar with the debate, and the latest arguments.
I think it's interesting to make an analogy with a sport like running. If you measure running ability in a group where every person has absolutely no training, all the differential in running ability will be genetic. But a person will be able to train and improve, and so a change in environment ran result in gains in ability. If some people in the group start to train harder, then the differential in scores will be a mix of environmental and genetic.
If you compare members of a cross country team who all endure the same grueling training, the differences in their running speeds will be genetic. If one member tries to train even harder, he will probably be unable to raise his speed even higher. At some point, he maxes out and no training will raise his speed even further.
The subtests that have a flat trend were vocab, math, and general knowledge. What this indicates is that the environment of a century ago maxed people out at these skills a century ago. This is not surprising, as these skills are the most culturally common skills. Even in 1900 a person had constant exposure to reading, math, and general knowledge.
The subtests that have seen the greatest rise are all obscure skills - object assembly, picture arrangement, similarities. My guess is that the great increase in schooling resulted in more training in these obscure skills. Increased availability of games and puzzle books also helped. In 1900 if you were a genius kid, you read the classics. In 2009 you can play all sorts of fun puzzle games online or in books. As a result of this, scores on these obscure puzzles have gone up.
The net of this may mean that the hardcore hereditarians ( Murray, Jensen) are wrong about the specifics but right about the big picture. They are wrong to think that differences in the Raven test by themselves mean that one group has more natural cognitive abilities than another group. But they are probably right that individual and group differences in the economically and socially useful cognitive skills are mostly genetic. The differences in the obscure cognitive skills ( Raven's, picture arrangement) may be much more environmental.