Every now and then, the media trumpets the discovery of a gene that is responsible for a particular behavioural trait, creating an impression in the general public that our behaviour is determined biologically. But how valid is this view?
I have remained interested in the issue of genes and behaviour for some time, because I find myself particularly curious about the gaping holes in our body of scientific knowledge, and the tendency for those with a scientistic worldview to ignore or overlook these holes when doing so serves their purposes. (Scientism, incidentally, is the ideology that science has primacy over other interpretations of life, that is, that scientific knowledge is more important than other forms of thought).
A brief history of the gene is required. In the 1860’s Gregor Mendel experimented with cross-breeding pea plants, and came up with principles of inheritance that are still taught today. He hypothesised, based on his observations, that there was a factor that transferred traits from parents to offspring. In 1909, Wilhelm Johannsen coined the term gene for this factor. During discussion in this era of science, all manner of properties were considered to be inherited – including physical traits, behavioural traits, and derived properties such as intelligence and even criminal tendency.
In 1953, Hershey and Chase demonstrated that it was DNA that contained genetic information (and not proteins, as was previously believed), and shortly after several different groups (including Watson and Crick) discovered the helical structure of DNA. There was much excitement in the scientific community, as it seemed that we had learned everything there was to know about inheritance – traits were encoded in genes in the DNA molecule, and this was inherited by the offspring.
However, something rather vital was missed out during this process of the development of ideas of genetics, specifically, it was assumed that everything that was discussed as an inherited trait prior to the discovery of DNA as the means of transmitting genetic information, was indeed transmitted via DNA. In the case of behaviour, this view persisted even in the total absence of any supporting data.
Genetics is a complex subject, but we only need to understand a few simple aspects to conduct this discussion. A gene is a collection of nucleotides that codes for one of two different things: either it is the blueprint for a protein, or it is produces RNA molecules that regulate genes (turn them on or off) or otherwise affect the production of proteins. (Modern research has complicated this view by showing that a gene can code for different proteins, and the DNA for a protein need not come from consecutive sequences, but these points are irrelevant to this discussion).
Let me reiterate this point, as it is crucial: a gene codes for a protein, or it affects the production of proteins. There is nothing else we currently know of that a gene does.
Why, then, is there such talk of a genetic basis of behaviour? Because if behaviour is rooted in genetics, either we are saying that a protein produces behaviour (which we shall see shortly is absurd), or we are claiming that behaviour emerges somehow from genes in a manner we don’t understand and cannot currently prove – at which point the honest scientific position is to admit that we do not know how behaviour is inherited.
Let us look at the claim that a protein produces behaviour by examining a specific case. In 1993, a well-publicised report was published in the journal Science recounting the work of Dean Hamer which claimed to have found a gene which correlated with homosexuality. The media trumpeted this research as having found “the gay gene”. This conclusion was later shown to be flawed, in particular, a study of homosexuality in identical twins demonstrated that homosexuality was not expressed in both twins. Furthermore, studies demonstrated that adoptive brothers show greater incidence of ‘shared’ homosexuality than non-twin biological brothers. This is extremely strong evidence that homosexuality is not genetic in basis.
And we should not be surprised by this, because if there were “a gay gene”, it would mean that there was a gay protein, and that the gay protein caused homosexuality. (This leads to the amusing notion of having a “gay protein shake” – would that make someone gay?) How can a single protein cause a complex behaviour? We have no model that allows for this, and indeed, what little we know of the biological basis for behaviour makes this an untenable claim. It makes for good media sound bites, but it makes for very poor science.
What is the evidence that behaviour is genetic? There is none, although there is some evidence that behaviour is inherited.
The strongest evidence relates to medical disorders. It is certainly the case that problems with specific genes (bugs in the genetic code, if you will) can cause alterations in behaviour. This is not dissimilar to observations that physical damage to the brain can change behaviour. But of course, what we mean when we talk of behaviour in the context of brain damage is not what we always mean when we talk of behaviour – when you try to chat up a potential romantic partner we can call that behaviour, but we are not using ‘behaviour’ in the same context as when we talk about the behaviour that results from damage to the brain.
There have been experiments that demonstrate that altering genes in mice can screw around with mouse behaviour, but this seems to be in the same kind of category – behaviour in the sense of a medical disorder is not the same as behaviour in general terms.
There is evidence that ‘behaviour breeds true’, that is that it is possible for behaviour to be inherited. For instance, consider the behaviour of specific dog breeds, such as the retrieval instinct of a Labrador. But this is evidence for the inheritance of behaviour, not for the genetic basis of behaviour. We can leap the burden of proof if we wish and jump straight to DNA as the basis of this inheritance (and it may not be wholly unreasonable to do so) – but it is not strictly scientific to do so. At best, the idea that all behaviour has a genetic basis is a hypothesis.
Finally, there is the relationship between species and behaviour – in that different species have different behaviours associated with them. But this cannot be considered evidence for a genetic basis for behaviour, since some behaviours alter in species in single generation steps (migration behaviour in birds, for instance) – which would be impossible if behaviour was determined by genes.
Where does this leave us on the subject of genes and behaviour?
The bottom line is that while virtually all behaviour can be influenced by genes, there is no evidence that behaviour is determined by genes. There is no gay gene, no gene for intelligence, no gene for violence, no gene for reliability, no gene for amiability… there is no gene for any behaviour, neither does it seem likely that any such gene will be found. Errors in genes can cause specific medical conditions (which have behaviours associated with them), as with Down’s syndrome for instance, but that is as far as the body of research currently goes.
In 1994, the journal Science published an article by Charles Mann entitles Genes and Behaviour which contained this apposite quote:
Time and time again, scientists have claimed that particular genes or chromosomal regions are associated with behavioral traits, only to withdraw their findings when they were not replicated. "Unfortunately," says Yale's [Dr. Joel] Gelernter, "it's hard to come up with many findings linking specific genes to complex human behaviors that have been replicated. "...All were announced with great fanfare; all were greeted unskeptically in the popular press; all are now in disrepute.
We are nowhere near to understanding the basis for behaviour, although we can say with confidence that complex behaviours do not result from single genes. Because the genes we inherit come in part from one parent, and in part from the other, attempts to tie behaviours to multiple genes seem equally flawed. Something else is going on, we don’t know what, and all we can really do is wait and see what future research turns up on the utterly mysterious subject of behaviour.