Genes and Behaviour

By Caroline Berry and Attila Sipos

With the DNA sequence of the human genome jotted down the hard work now begins of making sense of the data. A critical part of this is establishing the extent to which people’s behaviour is determined by their genetic make-up. The relationship between genes, environment and behaviour is vastly more complex than any simplistic concept of genetic determinism. Rather than being pre-programmed gene-machine, human beings are created in the image of a God who will hold us responsible for our action.

Serious study of the genetics of behaviour started with work on social invertebrates. By observing ants, biologist discovered that cooperative behaviour and create a cohesive society.

Researchers started to talk about ‘sociobiology’ when describing how altruism could be inherited; theories that originated with JBS Haldane and WD Hamilton in the 1960s.

Studies on higher vertebrates, particularly birds, show that patterns on behaviour that promote survival within families occur in stressful environments. Life began to be seen as an endless struggle to pass genes from one generation to the next.

Difficult to accommodate under the ‘survival of the fittest’ model was the self sacrificial behaviour that occurs in the animal world. This is seen when mothers sacrifice themselves for their offspring and when the sentinel wolf is sacrificed for the benefit of the pack.

To explain this, scientist developed ideas of ‘kin selection’ and the evolution of altruism. it proposed that as relatives share a proportion of their genes, the genes have a better chance of survival to the next generation if one individual enables a relative to survive, particularly if the relative is younger or more fit than oneself. This provides an explanation for how genetically determined altruistic acts might persist within the family of tribe.

Inevitably these ideas were extrapolated to explain human behaviour, initially by Harvard entomologist EO Wilson,1 with Richard Dawkins’ book the Selfish Gene2 being more widely known.

It is not only altruism that is said to have evolved. Utilitarian bioethicist Peter Singer wrote 20 years ago: ‘sociobiology… enables us to see ethics as a mode of human reasoning which develops in a group context… Its principles are not laws written up in heaven…’3

Edward Wilson, in his most recent book Consilience explains this view well. He believes that our choices between ‘good’ and ‘evil’ are in reality determined by our genetic endowment and our culture. As individuals, we have little freedom of choice. God is seen as a tribal chief with his power reinforced by myth and religious organization.

We can see that insects could be ‘hard wired’ with their behaviour largely genetically determined. But what determines behaviour in higher animals, in particular human beings? And how should Christians respond to the claims of people like Dawkins, Singer and Wilson?

Human Behaviour

Towards the end of the twentieth century studies suggested that genetic factors were relevant to a number of psychiatric disorders such as depression, alcoholism and panic attacks.4 These studies compared identical and non-identical twins, and compared children with either their biological or adoptive parents.

Today molecular genetics is the tool pf, choice and as work on the human genome proceeds, many of the single gene disorders have had the genes responsible for them identified.

Attention is now turning towards the commoner but such much more complex diseases such as diabetes, heart disease and asthma. Here we find multiple genes interacting with environmental factors so we can no longer talk of ‘genes for’ but rather ‘genes associated with’ or ‘predisposing to’.

This group illnesses also includes schizophrenia, depression and anxiety disorders. Despite years of extensive research, no one knows what causes them.4 Part of the problem is working out how to define the borderlines between health and disease. Severe schizophrenia is a devastating medical disease that responds to drug treatment, but those with milder forms may be viewed just as eccentric individuals.

Depression is even more intangible. When severe it is a serious disease, which again responds to medication. Feeling depressed can, however, be an appropriate response of healthy people who find themselves in stressful environments.

A Question of Shape
Our knowledge of brain chemistry and the function of substances like dopamine and serotonin is increasing. Current research focuses on identifying receptors and tries to establish their physical make-up.

We know that the exact shape of a drug receptors influences the effectiveness of its response. Variations in the molecular structure of receptors and other cellular molecules will therefore affect the strength of our response to our natural hormones and ‘chemicals’. But as we have already seen, these correlations are likely to be highly complex and dependent additionally on environmental factors.

Recently developed research tools are just beginning to provide a way of looking to see how specific genes interact with specific features of the environment.5

Being Me
While genetics is certainly involved in disease, could it also determine aspects of our personality? After all, we frequently read in newspaper of scientists finding ‘the gay gene’, ‘the gene for risk-taking’.

Sadly the excitement generated by these reports is out of proportion to their scientific validity. In addition repeat studies often fail to confirm the findings and these receive little publicity. Some of the hype is driven by the media’s need for sensational news, and partly by extreme press releases sent by either the scientists themselves, or by journals that published the study, seeking to draw attention to the work.

It often requires a few years from the initial announcement of a discovery before objective conclusion can start to be drawn.

For example in 1996 it was proposed that a variant of the dopamine D4 receptor gene was associated with novelty seeking.6 The finding was confirmed by some but discounted by others7 and explanations for the discrepancies then put forward.8 At the same time other observers were commenting that homosexual orientation was most probably influenced by both biological and psychosocial factors.9

Whatever the current state of ignorance, everyone accepts that increasing knowledge of the human genome will show that some genetic factors relate to certain behaviours.

Read more: “Nature or Nurture, Repercussions.. Refutation… (to be continue)

Christian Medical Fellowship (CMF) Files No. 14, 2001