Ausgabe 36/2010

How Hereditary Can Intelligence Be? Studies Show Nurture at Least as Important as Nature

Researchers have long overestimated the role our genes play in determining intelligence. As it turns out, cognitive skills do not depend on ethnicity, and are far more malleable than once thought. Targeted encouragement can help children from socially challenged families make better use of their potential.


Eric Turkheimer jokes about people who believe environmental influences alone determine a person's character: "They soon change their tune when they have a second child," he says. A father himself, he is speaking from experience. His eldest daughter likes being the center of attention, while her sister is shy and more reticent at school.

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Heft 36/2010
Warum so viele Deutsche einem Provokateur verfallen

Even so, Turkheimer doubts that genetics alone can provide the complete answer. As a clinical psychologist working at the University of Virginia in Charlottesville, he repeatedly came across people whose childhoods hadn't been as carefree as those of his daughters. Many of his patients are from impoverished backgrounds.

"I could see how poverty had literally suppressed these people's intelligence," 56-year-old Turkheimer says.

Scientists typically use twins to gauge the influence of our genes on the one hand and the environment on the other. However Turkheimer noticed that such studies rarely involve twins from broken homes. Stress, neglect and abuse can have a dramatic effect on intellectual ability. And it's precisely this factor that many nature-vs.-nurture studies have completely failed to address.

Plugging a Gap

Turkheimer and his colleagues are the first scientists to have plugged this gap. Their three studies conducted in the United States on this issue have now compared the intelligence of hundreds of twins from more privileged backgrounds with those from more difficult environments. They found that the higher a child's socioeconomic status, the greater the genetic influence on the difference in intelligence. The situation is very different for children from socially disadvantaged families, where differences in intelligence were hardly inherited at all.

"The IQ of the poorest twins appeared to be almost exclusively determined by their socioeconomic status," Turkheimer says. A person's intelligence can only truly blossom if the environment gives the brain what it desires.

Ulman Lindenberger, a 49-year-old psychologist at the Max Planck Institute for Education Research in Berlin, has come to the same conclusion. He says, "The proportion of genetic factors in intelligence differences depends on whether a person's environment enables him to fulfill his genetic potential." In other words: Seeds that are scattered on infertile soil won't ever grow into large plants.

This is precisely what intelligence researchers have denied up to now. Dazzled by their studies of carefree middle-class and upper middle-class twins, they decided that cognitive skills are largely under genetic control, that academic talent is biologically hard-wired and can unfurl in almost any environment.

'Intelligence Is Highly Modifiable by the Environment'

In the meantime psychologists, neuroscientists, and geneticists have developed a very different perspective. They now believe that the skill we term "intelligence" is not in the least fixed, but is actually remarkably variable. "It is now clear that intelligence is highly modifiable by the environment," says Richard Nisbett, a psychologist at the University of Michigan in Ann Arbor.

As a result, researchers have in recent years scaled back their estimates of the influence genetics plays in intelligence differences. The previous figure of 80 percent is outdated. Nisbett says that if you take social differences into account, you would find "50 percent to be the maximum contribution of genetics." That leaves an unexpectedly large proportion of a child's intelligence for parents, teachers and educators to shape.

The findings will undoubtedly please those parents who already send their children to good schools, drive them to violin lessons in the afternoon, and then drag them around museums at the weekend. "So you haven't wasted your time, money and patience on your children after all," Nisbett says.

Time and again researchers have found that a child's genes have far less of an effect on its brain than its surroundings -- and the social environment is only one of the factors in this. Scientists in Boston, for instance, have found that children who live near roads and intersections and are thus exposed to higher levels of exhaust fumes have three IQ points fewer on average than children of the same age living in areas with cleaner air. That's simply because microscopic dust and pollutants can reach the brain and then adversely effect the nerve cells' ability to function properly.

In a similar way to those exposed to pollutants, children also suffer as a result of mental pressure, misery, worry and neglect. Chronic stress alters the way neurotransmitters work, inhibits the formation of new nerve cells and causes the hippocampus to shrivel.

That can lead to identifiable differences, as researchers at Cornell University in Ithaca, New York, have shown. They found that stressed children from poor families performed up to 10 percent worse at memory tests than well looked-after children from middle-class homes.


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Norberto_Tyr 09/13/2010
1. Thinking is like digesting, a bodily function, as Schopenhauer would say
Thinking, the main operation of the brain, is like digestion to the stomach, merely a bodily function; then I do not know how the ability to think according to a-priori patterns imprinted in our brain operating under the forms of time and space could not be inherited as any other physical trait. On the other hand, the question about intelligence taxonomy, namely how this ability is distributed within the human kind is a completely different subject matter, let alone the definition of 'intelligence'. When an organized group of people attempts to take possession of the 'intelligence' definition in order to pump-up their rather floppy self-esteem we are up for mischief on a grand scale. Regardless of the rather diffuse definition of 'intelligence' suffering from well known limitations, the empowering industry of intelligence tests (imagine that you are able to classify people like in the Guinness books of records) allows a Babieca becoming a demigod generating million of US dollars (for what they worth since these 'assets' are someone's else liabilities) through books, lectures, reputation and entertainment. This is the proof of a theory I proposed long ago, namely that the professions we choose are compensation for our own perceived defects, for example, a person wishing to measure people's intelligence betrays his doubts on his own intelligence. By placing himself above the rest he avoids been tested himself, thus, a judge might be someone that thought of himself a liar when he was a kid, a journalist, someone that is trying to hide a personal secret so he fends himself discovering others, in the same way that 'Become a millionaire in one week' can only be written by someone doubting that that is possible, otherwise he would not have wasted weeks writing it. I see Sarrazin labeling people at willy-nilly within this context, I do see Wilders in the very same business as well. They doubt their own skills and talent therefore they believe that projecting their own inferiority complex to others are protecting themselves. This is a serious problem, as demonstrated by history, even though they cannot fool themselves they might be able to fool others, and that is dangerous. For instance, in the recent past someone was caught unexpectedly in an incredibly precarious situation as it was, apparently, incredibly successful, the problem was that all his victims mistakenly believed that he was the source of the success, and of course, he could not disappoint them. Now, a sensible person would have had taken advantage of the situation by loosing prestige but saving the day, but not, prestige was his only asset so he doubled the bet over and over again until it was utterly unsustainable, then he laconically said: 'ok, I quit', so he would not witness people witnessing that the king was naked. This proves another theory, a disability can become an asset, and vice versa. For example, a group of people lacking talent might protect themselves combining and supporting each other regardless. Kissinger I believe once said: 'successful defensive strategies gradually shift to the offensive'. Yes, a real or perceived threat can trigger this behavior. We must not dismiss the fact that the disappearance of the threat would deflate the power of that strategy, especially when is used on the offensive. There is another danger, people believing that have suffered certain fate real or imaginary might attempt to repeat that onto others. An old adage says that you test the worth of a man by granting him power, Mandela's restraint is a case in point. True, give them power and see what they do with that power, especially with utterly defenseless people like Roma people in France, for instance, and also beyond. Finding common denominators is also a common technique to detect 'intelligence'. On the other hand, I would like to propose an intuitive 'definition' for 'intelligence', I prefer the idea of 'art' because is universal. Cultures are based on art, and art is not a cacophonic arrangement of ideas combined at random lacking either plan or basic technique (Jazz has technique but not the plan and Piet Mondrian's pictures (et al) have a plan but not technique, for example). Art is planned and people with sensibility do not need training to appreciate it. A westerner can easily appreciate Keops, or the Taj Mahal and Liu Ts'ai's fishes; conversely, an Oriental person can appreciate Vivaldi, Bach and Mozart perfectly well; we can also appreciate art across time (Altamira's paintings and good Picassos). What would do a Lascaux caveman genius with an 'intelligence' test ? I have an idea though. Well, I am running out of the number of characters graciously granted by Der Spiegel, so we must leave as it is, food for thought, but before we go let me express that I do not see Sarrazin as an exception but rather the norm of the XXI century, unfortunately. Norberto
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