IQ by inheritance
Genetics and intelligence
Psychogeneticist Robert Plomin – about IQ tests, the Flynn effect and genetic predisposition to higher or lower intelligence.
The question of intelligence is one of the oldest in psychogenetics. It dates back to the research of the English anthropologist Francis Galton in the second half of the XIX century. Galton, Darwin's cousin, was one of the first to study people whom others considered intelligent.
How to evaluate intelligence
In the early 1900s, quantitative assessments of intelligence were created. The English psychologist Charles Spearman in 1904 wondered what we mean when we talk about intelligence if everyone understands it differently. Spearman called intelligence general cognitive abilities – the G factor.
There are hundreds of tests for cognitive abilities. They are used to test different types of memory, language proficiency, vocabulary, and spatial orientation abilities. Cognitive abilities are interconnected, so if a person is fine with speech, then he probably has a good memory and is well-oriented in space. The G factor is all that is common in the tests. The results of completely different, verbal and nonverbal, intelligence tests show IQ – a quantitative assessment of general cognitive abilities. Factor G is important because it predicts socially important things – the result of education and employment – better than other indicators, and these results are inheritable.
Neuroscientists are showing more and more interest in the issues of intelligence, it helps to understand how the brain works and functions. Previously, neuropsychologists believed that specific areas of the brain were responsible for different actions, the activity of which could be traced during functional MRI. But the brain has evolved as a global tool for solving problems, that is, it simultaneously uses all the resources available to it.
The G factor is best shown by tests for abstract thinking and problem solving in unfamiliar situations. That's what makes really smart people stand out, not the number of facts they've memorized. That is, the G factor, intelligence, is, in fact, the ability to learn. For some children, studying is easier. We will not consider the influence of the environment, but try to trace the connection with genetics.
Is it possible to inherit intelligence
Heritability describes to what extent the differences observed between us are related to genetics. It seems logical to assume that heritability decreases over time due to differences in the environment, accidents, diseases. And the longer people live, the more differences between them should be related to the influence of the environment. In fact, the situation is diametrically opposite, and studies have shown that the heritability of intelligence only grows over time.
Psychogeneticists know that individual differences in the level of intelligence are inherited. An array of works in this field – hundreds of studies of twins, foster children and their families – shows 50% heritability. There is a linear increase in the heritability of intelligence: in infancy – 20%, in childhood and adolescence – 40%, in adulthood – 60%, and in late life – 80%.
The results of intelligence tests are not programmed in DNA, genes only make it easier for you to learn. You can study more complex disciplines and choose an environment that corresponds to them, in which it is comfortable to read serious works, engage in discussions, communicate with those who like to discuss intellectual issues. In this way, you create living conditions that correlate with genetic inclinations. Small differences, which reach 20% in infancy, grow like a snowball over the course of life, when a person chooses an environment that corresponds to his genetic predisposition. Therefore, the heritability of intelligence increases throughout life, and this should be taken into account in education.
What does academic success depend on?
More children are tested in England than anywhere else in the world. We found that in the first year of study, literacy and numeracy – what we teach in schools – are inherited by about 65%. The differences between children, even when they come to school, are mainly due to genetic factors. Then the heritability of intelligence goes up. And if in the first few years of study the heritability of school achievements is higher than the heritability of intelligence, then later, when the heritability of intelligence grows, they become almost equal.
Academic achievements are equally inherited in both natural and exact subjects, as well as in the humanities. Many genetic influences overlap: the same genes are responsible for studying both mathematics and English. For the most part, we call them intelligence.
How individual differences change
We usually look at individual differences: why people have such different intelligence and educational achievements. There is considerable interest in the question of the growth of intelligence. The gradual increase in IQ scores is called the Flynn effect. New Zealand philosopher James Flynn in the 1980s published a paper in which he noted that in the last few decades there has been a great increase in the level of intelligence. Apparently, it has slowed down slightly now, but no one knows exactly what is the matter. Either we are doing more complex tests, or it is the consequences of standardization methods.
We must admit that the reasons for the differences between us and people who lived fifty years ago are not necessarily related to individual differences. A good example of this is the obesity epidemic. People are not only becoming smarter, but also gaining weight, and this is especially noticeable in developed countries. Such changes must be related to the environment: they are too fast for genetics. But the heritability of weight has also been high for decades.
We interviewed people, finding out how much, in their opinion, a person's height is inherited. Respondents answered: "Extremely strong, by 90%", implying that most of the differences are related to genetics. Then we asked a similar question about weight. People believe that it is inherited by 30-40%. In fact, by 60-70%: most of our weight differences are due to inherited differences in DNA. Even if we gain weight over the decades, heritability remains high because the causes of individual differences are not necessarily related to the causes of average differences. There is a high probability that our brain is still living in the Stone Age and wants to accumulate fat. It's good if you don't know when you'll be able to eat next time, but not in the age of fast food, where you are inundated with food from all sides. In this case, people who have a genetic predisposition will gain weight.
It is interesting to think about heritability from the point of view of the environment. It is possible to get rid of all differences in society, exclude privileged positions and prohibit inheriting parents' money. But you can't get rid of genetic differences. Other things being equal, heritability is growing, which means that this is an index of social mobility.
It is important that we are talking about the influence of genes on behavior within a particular population at a given time with a certain ratio of genetic factors and environmental factors. We describe what is, not what could be. But suppose the conditions have changed. For example, how will heritability change in the post-apocalyptic world of Mad Max, where the environment is completely different? Under such conditions, heritability would probably increase as genetic differences would become more important. You would have to deal with life and death issues all the time. You would not be able to live on autopilot, as we do in our relatively civilized world, where we are not often surprised by what is happening.
It is difficult to know for sure what will happen in the future and what the environment will be like. But if you equalize the conditions, the heritability will increase. And this is a really interesting question about equality of opportunity: it implies that heritability is an index of equal surrounding circumstances.
This lecture was published as part of the project Serious Science, created by the post-Science team. Here you can see the original version.
About the author:
Robert Plomin – Professor of Behavioural Genetics, King's College London
Portal "Eternal youth" http://vechnayamolodost.ru