Some years ago, acting as an archaeologist, I amassed a large body of data showing that IQ tests had gotten easier. Over the twentieth century, the average person was getting many more items correct on tests like Raven's and Similarities. The response of intelligence- or g-metricians was dual [Editor's note: See here for an exploration of the "general intelligence" factor g]. First, they distinguished IQ tests as measuring instruments from the trait being measured, that is, from intelligence (or g if you will). Second, they noted that in the absence of an absolute scale of measurement, the mere fact that the tests had gotten easier told us nothing about whether the trait was being enhanced. IQ tests were only relative scales of measurement ranking the members of a group in terms of items they found easy to items they found difficult. A radical shift in the ease/difficulty of items meant all bets were off. At this point, the g-metrician decides that he cannot do his job of measurement and begins to look for an absolute measure that would allow him to do so (perhaps reaction times or inspection times).
However, as a cognitive historian, this was where I began to get excited. Why had the items gotten so much easier over time? Where was the alteration in our mental weaponry that was analogous to the transition from the rifle to the machine gun? This meant returning to the role of archaeologist and finding battlefields of the mind that distinguished 1900 from the year 2000. I found evidence of a profound shift from an exclusively utilitarian attitude to concrete reality toward a new attitude. Increasingly, people felt it was important to classify concrete reality (in terms the more abstract the better); and to take the hypothetical seriously (which freed logic to deal with not only imagined situations but also symbols that had no concrete referents).
It was the initial artifacts that caused all the trouble. Because they were performances on IQ tests, and IQ tests are instruments of measurement, the roles of the cognitive historian and the g-metrician were confused. Finding the causes and developing the implications of a shift in habits of mind over time is simply not equivalent to a task of measurement, even the measurement of intelligence. Now all should see that different concepts dominate two spheres: society's demands—whose evolution from one generation to the next dominates the realm of cognitive history; and g—which measures individual differences in cognitive ability. And just as the g-metrician should not undervalue the non-measurement task of the historian, so the historian does nothing to devalue the measurement of which individuals are most likely to learn fastest and best when compared to one another.
I have used an analogy to break the steel chain of ideas that circumscribed our ability to see the light IQ gains shed on cognitive history. I hope it will convince psychometricans that my interpretation of the significance of IQ gains over time is not adversarial. No one is disputing their right to use whatever constructs are best to do their job: measuring cognitive skill differences between people.
But an analogy that clarifies one thing can introduce a new confusion. The reciprocal causation between developing new weapons and the physique of marksmen is a shadow of the interaction between developing new habits of mind and the brain.
The new weapons were a technological development of something outside our selves that had minimal impact on biology. Perhaps our trigger fingers got slightly different exercise when we fired a machine gun rather than a musket. But the evolution from preoccupation with the concrete and the literal to the abstract and hypothetical was a profound change within our minds that involved new problem-solving activities.