Every year in England there is a scientific jamboree held by the British Association for Science at which leading scientists from the whole gamut of current research give talks for the intelligent layman and brief reports of these are published in some of the broadsheet newspapers. Among the talks this year was a report by Prof Plomin, one of the world's leading researchers into the genetic basis of intelligence who, with his team at Institute of Psychiatry, is currently digesting the results of one of the largest surveys of identical and non-identical twins ever undertaken.

One of Prof Plomin's early results is that there are no specific genes that can be unambiguously labelled as genes for intelligence. There are, however, important 'general' genes which are involved in the design of the brain, its development in the foetus (and for years later) and its maintenance. But some of these genes will also be involved at much earlier stages in the development of other parts of the foetus, not just the brain. In the coming year or so, Prof Plomin will undoubtedly be able to identify a number of genes -- probably a large number -- that are involved in the whole business of producing a working brain that is adequate for the survival activities of an individual.

Although each gene is responsible for the production of a specific protein molecule that is used in the construction of the body it is, in turn, controlled by other molecules called nucleosomes which normally act as a tight sheath wrapped around the twin coil of the DNA molecule. This sheath occasionally relaxes enough to allow the DNA coil to untwine at one place or another and expose a gene, allowing it to do its stuff. In turn, the nucleosome is produced by other genes and how long it is either relaxed or tightly wrapped depends on those genes and also on the shape of the overall molecule and the lengths of what is known as "junk DNA" which separates one gene from another along the length of the DNA. At any one instant of time, quite what the chromosome (the whole length of the DNA molecule) is doing depends on its overall, very complex, shape. Parts of it will be tightly coiled, held rigidly by the nucleosomes, other parts will be exposed, and the chromosome will be constantly changing its shape in what must be the most complex dance in the whole of the universe.

Thus what Prof Plomin and his team have shown so far is that there are many genes involved in the formation of the brain and no single one of them can be chosen as being specific for one mental ability or another (even if particular mental abilities can be so defined). The overall ability of an individual's brain depends therefore not only on a large number of genes but also the particular choreography of the dance that a chromosome will be making. Even in the highly unlikely instance that one individual's chromosome contains exactly the same genes as another individual's, their chromosomes may dance slightly differently -- their pauses, and progressions from one shape to another (and the consequent production of proteins) may be slightly different.

The ongoing dance of the chromosome may also depend on the particular circumstances in which the individual person may find himself or herself at that moment and, furthermore, on his or her decisions to remain in those circumstances or whether to change them or to move bodily to another set of circumstances. So the environment comes into the picture, as also does that indefinable thing called freewill. Of course, the environment can't in any way change the genes that lie on the chromosome but, within limitations, it can entice the chromosome to dance slightly differently in one way or another -- to slow down or quicken at some stages.

Overall, therefore, the ability of an individuals' chromosome to adapt the choreography of the ongoing dance depends very importantly on the environment. There's a certain amount of leeway but only within well-defined limits according to the specific genes lying along the chromosome. If a particular circumstance of the environment requires a certain response of the individual but it lies outside the ability of his or her chromosomes to adapt their choreographies, then that individual cannot perform adequately. In some extreme circumstances this shortfall may even result in the death of the indvidual with the consequence that his or her particular genes will not be passed on to the next generation.

Thus we have a slightly more detailed description of Darwin's theory of the survival of the fittest individuals within a particular environment. However, what must be said in these modern times is that the environment not only depends on obvious external circumstances -- such as temperature and so forth -- but also on the way we operate every day in the business of earning a living and raising a family. Thus, if the general skill level of a country's economy rises, then only the more intelligent will thrive at the expense of the others.

Of course, what consitutes "intelligence" can only be defined in terms of what we consider to be important attributes at any one time in history, and these in turn depend on the particular character of the economy and the pattern of jobs that it contains. The score of an individual's IQ test and the skill requirements of an economy don't have absolute values but are mutually dependent. Therefore, the abilities that are measured by an IQ test are important for the differential survival of one person or another in a modern economy -- assuming that the individuals who prosper are more successful in raising children than other who don't. Because (as described in "087. Tomorrow's job solution") the skill levels of modern developed countries are rising all the time, we cannot escape the effect of this changing environment on the selection of mental abilities.

Whether the family size of the more intelligent is more than the replacement level of 2.2 children or whether governmental policies enable the families of the less intelligent who are unable to get jobs in an increasingly skilful economy to achieve 2.2 children is a political matter outside the scope of this discussion.

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BRITISH ASSOCIATION Meeting at Salford University

Study of twins dashes learning disability hope

Clive Cookson

Britain's largest ever study of twins appears to have dashed hopes of finding specific genes to account for learning disabilities.

Scientists gathered at Salford University were told yesterday that one large set of general genes determined the entire range of mental ability from genius through to severe language impairment. Robert Plomin, deputy director of the Institute of Psychiatry, London, outlined the "surprising" conclusions of the Twins Early Development Study to the science festival. The study is following the psychological and educational progress of 7,500 pairs of twins born in England from 1994 to 1996.

"Genes that affect learning disabilities in the early school years are generalists rather than specialists in three ways," Prof Plomin said. First, the genes that affected disabilities were the same as the ones that determined normal variation in abilities. Second, genes were general in their effects on many aspects of a learning disability. Third, genes that affected one learning disorder also affected other disabilities.

Prof Plomin reached his conclusions by comparing the results of identical and non-identical twins on a range of tests, including verbal and non-verbal IQ, maths and reading. Overall he found that genes accounted for about 60 per cent of learning problems.

"Stated dramatically, these findings suggest that there are no disabilities, just the quantitative extreme of the normal bell-shaped curve of variation in abilities," said Prof Plomin, an American who has aroused controversy in the past by investigating the genetic foundations of intelligence.

Although some rare mental problems are caused by single genes, these do not play a part in the story of common learning disabilities typically seen by parents and teachers. The results support the concept of general cognitive ability or "g", first advocated by Charles Spearman 100 years ago. " 'g' is probably not a single brain process but rather the co-ordinated efficiency of many aspects of the brain working together to solve problems," Prof Plomin said. "It makes sense that our brain evolved to function not as independent bits but rather as a co-ordinated whole, using everything we've got in order to survive."

Prof Plomin does not expect the educational establishment, which is wedded to the concept of separate learning disabilities, to take kindly to his conclusions. "Education is the last bastion of anti-genetics," he said. "It is like 20 years ago in the rest of psychology."

The next step in the research will involve analysing the twins' DNA to look for the unknown -- but probably large -- number of generalist genes that combine with environmental factors to cause common learning difficulties.

Financial Times; Sep 10, 2003

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