The flynn effect refers to the substantial increase in average IQ seen in western societies since Binet started testing IQ scores in the 19th century. An average person living one hundred years ago would score about 70 on a modern IQ test, which happens to also be the cutoff score for mental retardation. Were our ancestors really retards?
How can this be the case given that we know that IQ is highly heritable (60 to 80 percent of the variance is explained by genes)? I believe (and I believe others believe this), that IQ is highly heritable given a relatively modern environment. What distinguishes our modern society from the society a hundred years ago is that today we deal with abstractions and categorizations all the time. Computers and the internet is based on interactions with representations of things i.e., abstractions.
Similarly, according to James Flynn (see video), there has been a notable shift in tasks that children encounter in school. A hundred years ago, tasks and examples were almost entirely based on concrete examples about things the students would encounter. Today, almost all tasks are abstract, requiring imagination of things you may or may not have seen.
The shift is also evidenced by the fact that many people living in traditional societies, whose lifestyles are more similar to that of our ancestors, are unwilling or incapable of thinking about abstract things. In the video, James Flynn talk about a conversation between an anthropologist and a native of some traditional society (cannot remember which). The anthropologist asks the man to imagine that in a country where there is always snow, bears will be white. If there is always snow in Greenland then what color will the bears be? Despite this relativeThe native insisted that to know this he would have to go and take a look or send a trusted associate to have a look. Thinking in what if terms was not a possibility...
IQ tests are to a large extent a measure of our ability to think about abstract things. This ability is undoubtedly a product of both nature and nurture. I would predict that if we could send a modern baby back a hundred years and be raised in that environment, that child would not get a great IQ score. Still this does not mean that IQ is not heritable. The variance in a population where all individuals encounter abstractions frequently (this is definitely the case in modern western nations), is likely to depend on genes. It is simply easier for some individuals.
I often hear that IQ is just "one type of intelligence" and it is often suggested that IQ doesn't matter. While IQ is not all that matters, there is a lot of evidence showing that IQ scores correlate with performance on a number of tasks and work. Your score on an IQ test is also one of the best predictors of life happiness. Our improved ability to think in abstract terms is likely to be have many positive effects. James Flynn takes about an older relative of his, who was incapable of thinking about hypothetical situations that people could encounter in other parts of the world. Our ability to reason abstractly allows us to take the perspective of other people in other parts of the world. I believe that this is a crucial ingredient in the improving global society we are seeing.
Were our ancestors retarded? Probably the answer is yes and no. If they had grown up in our society they would have become as good as us at reasoning abstractly, but since this was not the case they were probably somewhat retarded, at least in certain areas