Genetic research means we might identify what causes previously intractable illnesses and disorders. Four thousand of the estimated 50,000 to 100,000 genes that provide the blueprint for our development have been identified. Almost all of them may be known within a decade.
This research once concentrated almost exclusively on explaining hereditary components in conditions such as haemophilia or disorders such as schizophrenia. Yet it may be possible soon to test every facet of our genetic inheritance. Some of the most radical new geneticists say it is becoming possible to identify genes which may encourage depression, religious commitment and alcoholism.
It is this development which worries people who fear genetic discoveries will be misused to stigmatise groups of people. More prosaically, the idea that we might find genetic explanations for behaviour throws up a host of ethical and moral questions. Could gene tests be used to discriminate against people in employment or insurance? Could genetic engineering create a master race of children with perfect personalities and features?
Here, we publish an essay by Professor Michael Rutter, arguably Britain's leading genetic researcher and certainly one of its most controversial. He argues for a new synthesis between nature and nurture, genetic and environmental explanations for behaviour, a synthesis which allows for the influence of genetics, but only by admitting how complex that influence is. We plan further contributions to the genetics debate in coming weeks.
The old-fashioned notion that nature and nurture act as separate, independent influences is dead. Rather, genetic evidence has been crucial in indicating how the interplay between the two may operate. Of course, to study that interplay, it is necessary to use research methods that differentiate genetic and environmental effects. Advances in molecular genetics that allow actual genes to be identified take things a step further. We can now find out what genes actually do. Genes "code for" (influence) proteins, not behaviour; it makes no sense to talk of a gene for crime. The path between a gene, the protein it produces and behaviour involves a new search, which will be indirect and uncertain, dealing in tendencies and possibilities.
Quantitative genetic studies have shown that both genetic and environmental factors are influential in variations in almost all kinds of human behaviour. The relative strength of genetic and environmental effects varies across behaviour, as well as across social circumstances. Nevertheless, it would be a fair generalisation to say the strength of genetic and environmental effects on human behaviour is roughly equal.
That does not sound a very exciting conclusion but it incorporates some findings that shape our thinking about nature and nurture in several important, and surprising, ways.
To begin with, it firmly rejects any biologically deterministic view that genes could directly cause human behaviours. That is not how genes work and, in any case, environmental influences play a major role. Yet there is an equally necessary parallel rejection of environmental determinism.
People vary enormously in their behaviour; in part, this may reflect their upbringing or social circumstances, but in an equal part, it is likely to reflect their genes.
Three aspects of this finding tend to take people aback. First, genetics can affect characteristics such as religiosity or empathy as well as disorders such as schizophrenia or autism. It is not that genes determine religious beliefs; that would be ridiculous. But they do play a contributory (not deterministic) role in shaping personality features that influence how likely it is that a person will become heavily committed to religious beliefs. Genes, of course, will not determine the specific content of those beliefs.
Second, genetics also affects differences in people's experiences of stress or adversity. Initially, that sounds implausible, but genes come into the picture in two main ways. Parents pass on genes as well as experiences to their children and, to some extent, the two are connected. Parents who get drunk and quarrel are providing a discordant, disruptive family environment. But genes will be playing a role in the personality characteristics that make them such difficult parents and these genes will be passed on, too. It becomes an important question - do behavioural risks to children reared in such families come from genes or environment (or a mixture of the two).
The other role of genes comes from the fact that, by our behaviour, we all shape and select our environments. For example, some children are popular, well-liked by all, and tend to be the centre of rewarding "fun" activities. Others are disliked, rejected or isolated, left out of birthday parties and last chosen for favoured activities. The life experiences of these two groups of children will be quite different, and that will influence their behaviour. But the fact that their experiences are so different will be in part a consequence of what they are like as people, and genes will have helped shape those personal characteristics.
The third finding that tends to surprise people is that genes can influence traits such as sociability or emotionality, and not just diseases. Such genetically influenced characteristics play an important part in making people susceptible to serious mental disorders.
There is a general recognition that some diseases are inherited; most people know about cystic fibrosis or haemophilia. In the field of mental disorders, too, it is recognised that there are rare hereditary conditions such as Huntington's disease. How could the same thinking apply to depression, alcoholism or antisocial behaviour? It doesn't. But most medical conditions have multiple causes. For example, you don't inherit heart attacks, but genetic factors play a role in cholesterol levels and these constitute part of the risk pattern behind coronary artery disease.
Take another example. A few weeks ago, two groups of scientists reported localising a gene that contributed to a personality feature usually called novelty seeking or sensation seeking. Two aspects of this finding aroused excitement in the scientific community; first, this feature plays a part in the liability to engage in anti-social behaviour and, second, the gene is concerned with neurotransmitters in the brain thought to influence behaviour.
It is too early as yet to know whether the finding will hold up but it carries the promise of beginning to understand how genetic factors might play a role in some types of anti-social behaviour. If science could deliver on that promise, it would be immensely useful in planning better programmes of prevention and intervention.
Some crucial caveats, however, have to be inserted. First, sensation- seeking is only one of several factors that might be behind anti-social behaviour; in no way does it constitute the cause. Second, seeking novelty is not in itself a bad thing. It may lead to mountaineering, or the stock market or scientific discovery, or crime. The next challenge, then, is to discover circumstances which lead this trait to have beneficial outcomes rather than adverse ones.
Three consequences follow. Genes cannot be divided into "good" genes and "bad" genes. Only very rarely will it make sense to think of gene therapy to replace supposedly "bad" genes. As several genes are involved and because they are influential only alongside environmental factors, genetic discoveries should not be used to label individuals. The potential of genetic research lies in the discovery of how causal processes work and not in individual prediction.
A crucial feature of genetic studies lies in their power to demonstrate the true extent of environmental influences of behaviour. A few examples serve to illustrate this little-appreciated strength of genetic research. A study of twins, which makes it easier to identify genetic and environmental influences, has shown that much of the genetic risk of people having major depressive disorders lies in the genetic influence on the development of neuroticism, or emotionality. This genetic influence seems to operate, in part, by creating a vulnerability to environmental stresses.
A more striking example is schizophrenia, a mental disorder that involves a strong genetic component. Psychiatrists have long been puzzled by the observation that schizophrenia is much commoner in people in the UK of Afro-Caribbean origin. The finding that it is not more common in those actually living in the Caribbean points strongly to the operation of some sort of environmentally mediated, psycho-social risk.
This whole field of research points to some important issues for which some sort of environmental explanation is likely to be required. For example, the rise in recent decades in frequency of suicide in young males (but not in older people) cannot be attributed to genes - the gene pool does not change that quickly. Similarly, the explanation for the US murder rate being 15 times that in the UK will not be due to genes (it is more likely due to lack of gun control).
If the challenge of understanding how the interplay operates is to be met, genetic researchers, psychosocial researchers and developmental researchers must work together in ways that has happened all too rarely in the past. That is what the Social, Genetic, and Developmental Psychiatry Research Centre has been set up to achieve.
Professor Michael Rutter is honorary director of the MRC Child Psychiatry Unit, Institute of Psychiatry, in London.