Flynn in his 2007 book What Is Intelligence? further expanded on this theory. Environmental changes resulting from modernization — such as more intellectually demanding work, greater use of technology and smaller families — have meant that a much larger proportion of people are more accustomed to manipulating abstract concepts such as hypotheses and categories than a century ago. Substantial portions of IQ tests deal with these abilities. Flynn gives, as an example, the question 'What do a dog and a rabbit have in common?' A modern respondent might say they are both mammals (an abstract, or a priori answer, which depends only on the meanings of the words 'dog' and 'rabbit' ), whereas someone a century ago might have said that humans catch rabbits with dogs (a concrete, or a posteriori answer, which depended on what happened to be the case at that time).
“Reg Park’s theory was that first you have to build the mass and then chisel it down to get the quality; you work on your body the way a sculptor would work on a piece of clay or wood or steel. You rough it out””the more carefully, the more thoroughly, the better”” then you start to cut and define. You work it down gradually until it’s ready to be rubbed and polished. And that’s when you really know about the foundation. Then all the faults of poor early training stand out as hopeless, almost irreparable flaws. [..]