Over the last century and a half, stigmatising labels of pathology and 'disorder' have played a key role in the exclusion and sometimes inhumane treatment of people with same-sex attraction (SSA). As we saw in Martin Hallett's article in this issue of Nucleus (pp14-20), Christians have much more to do in combatting discrimination towards people with SSA and showing the inclusiveness of the gospel.
But the current debate about human sexuality is not simply about the need for inclusion. It is about what inclusion means. It is about what the Bible teaches. Christians who try to follow the teaching of the Bible believe that sexual attractions and desires need to be ordered within the framework of what God wants for human relationships. In other words, we believe that we are all included in the call to be obedient to Jesus Christ. In this part of the debate there can be ignorance and prejudice on all sides. The attitudes of some gay-affirming activists can also be characterised by irrational hostility to Christians who hold these views. Yet disagreement about certain forms of sexual behaviour does not necessarily constitute bigotry or exclusion.
There are disagreements, too, about how we interpret the scientific and psychological evidence. It is important to remember that these disciplines can only answer certain types of questions. Neuroscientists can help us to understand behaviours, but they cannot tell us whether those behaviours are right or wrong. Psychiatrists and psychologists can give us clues to understanding the factors that predispose people to different behaviours, but they cannot legitimise or provide a moral evaluation of those behaviours.
Let me give you an example. It is likely that, at some point in the future, biological factors will be found which may predispose certain people to promiscuous behaviour. This could be mediated through mechanisms regulating sensation seeking or impulse control. Genetics may contribute in some way. But this does not mean that those individuals are unable to exercise choice in the way they manage and express their inner world of impulse and desire. More importantly, it does not mean that promiscuous behaviour is somehow 'right'.
The values by which we choose to shape our behaviour cannot be decided by science. And there is no evidence to suggest that psychologists, psychiatrists or other secular professionals have special skills in determining whether, or in what circumstances, the expression of erotic sexual desires should be given priority over conflicting religious and moral values. Deciding between different value systems is a moral, ethical and theological matter - not a 'scientific' enterprise. We need to be clear about the limits of what science and psychology can actually contribute to the current debate over human sexuality.
But these limitations do not mean that science and psychology have nothing to say. On the contrary, our 'scientific' understanding of human sexuality raises a number of important issues, and we turn now to address these in detail.
First, what does the epidemiological and psychometric evidence tell us about the concept of sexual 'orientation' itself? What is 'gay'? Labels such as 'homosexual' and 'heterosexual' have only become popular over the last century, a relatively recent development in western culture. Researchers still disagree about how these labels should be defined  and attempts to identify and validate different 'orientations' on the basis of underlying biological factors have not been successful.
Patterns of SSA can be understood either in terms of differences of feelings and desire, differences of types of behaviour, the various labels that people choose to apply to themselves, or some combination of all three. Studies suggest that there are cultural variations in the way these differences are expressed. [2,3] And even in western cultures, estimates of the proportion of people with SSA differ, sometimes markedly, depending upon the particular concept of 'orientation' being used. [4-7]
Even when studies have attempted to use broadly comparable definitions of 'orientation', rates of SSA appear to vary in different populations. This may be due to unreliable methods used to measure SSA or real differences caused by social, cultural and biological factors; we do not know. Overall, however, studies [7-9] suggest that significant numbers of people from western populations, around 10-15% of men and 20-25% of women, experience a degree of SSA at some time in their lives. A much smaller proportion appear to be 'predominantly' same-sex attracted, probably about 2.0-2.5% of men and 1.5-1.75% of women. Prevalence rates of SSA in non-western populations have not been reported reliably, but ethnographic studies (a qualitative method used to study cultural phenomena, often involving months or years of fieldwork) report varying patterns of cultural expression of same-sex behaviour and desire. [3,10]
These different patterns of attraction are not necessarily stable. Whilst some people report a relatively constant experience of SSA since adolescence, others report mixed same-sex and other-sex attractions occurring at different points in their life course.  Some individuals appear to experience these mixed feelings only in their adolescent years, whereas others continue to experience mixed desires throughout adult life. There is also evidence to suggest that patterns of reported SSA can change over time; some individuals report first experiences of same-sex or other-sex attraction in later adult life.
For example, Sue Wilkinson, professor of Feminist and Health Studies at Loughborough University, was quoted in the Times saying:
I was never unsure about my sexuality throughout my teens or 20s. I was a happy heterosexual and had no doubts. Then I changed, through political activity and feminism, spending time with women's organisations. It opened my mind to the possibility of a lesbian identity. 
Whilst this experience of flexibility of sexual desire applies to some people with SSA, it would be wrong to think that it applies to all people or even to the majority. Better research is needed in this area. In the meantime, it is probably safest to think of sexual attractions as lying on a spectrum, with people at either end who are predominantly attracted one way or the other.
So we see that the question 'what is gay?' is a complicated one. Some people insist that the only valid 'label' is the one we choose to give to ourselves. For them, the term 'gay' may form a critical part of their self concept. Christians, however, would insist that their identity 'in Christ' is the defining principle of their lives, whatever their experience of different sexual desires.
Is there a gay gene? Well, no. The best evidence of a genetic contribution comes from studies that compare identical (monozygotic) with non-identical (dizygotic) twins. Early studies of concordance rates suggested that the genetic contribution might be fairly significant, with rates of around 50%.  There were problems with potential selection biases however. For example, some subjects may have come forward because they knew that they had twins who also had SSA. Recently, more epidemiologically robust studies (such as those utilising population based twin registries) have produced much lower concordance rates of 20% and less.  Francis Collins, who leads the Human Genome Project, has estimated that the heritability of homosexuality is about 20%.  Although the concept of heritability is complicated, this estimate is extremely modest if we recall that complex personality traits such as 'agreeableness' have heritability estimates of about 45%. 
A few years ago, a genetic linkage study by Dean Hamer found an area on the X chromosome, Xq28, linked to homosexuality.  As with so many other false dawns from linkage studies, this has never been satisfactorily replicated. It is much more likely that the small genetic contribution to different patterns of SSA is complex and involves several pathways of influence, operating by way of gene-environment interactions.
What about brain differences? A highly publicised study by Simon LeVay reported differences in the hypothalamus in a sample of gay men.  However, this also had serious methodological problems and it has never been satisfactorily replicated. The only finding to hold up consistently is an association between SSA and higher birth order in boys.  This has led to the hypothesis that the mother may be sensitised to some aspect of masculine hormone status, causing an immune-type response that gets stronger with each male pregnancy. If this immune response was to influence critical components in processes of sexualisation of the fetal brain, then younger brothers may have an increased chance of becoming homosexual. This is an interesting theory and there have been hints of hormonal data supporting it,  but there is no conclusive evidence so far. In any event, the effect is likely to be small, and differences in the social environment may provide an alternative explanation. The jury is still out on this one.
Of course, Sigmund Freud had a great deal to say about sexuality. His ideas about the process of 'normal' heterosexual development were set out in his classic 'Oedipal' theory. In this model, the male child relinquishes his mother as an object of sexual desire, identifies with his father, and replaces his mother with other women. According to Freud, male homosexuality results from a subversion of this process, often in the context of an over-involved mother and/or a cool, emotionally distant father.
Variations on the Oedipus theory formed the foundations for the pathologisation of homosexuality that held sway in psychoanalytic circles for much of the 20th century, especially in the United States. And psychoanalytic theory (developed by Freud, explaining our behaviours and emotions in terms of unconscious processes linked to childhood experiences) spawned a variety of other developmental models of homosexual development. All of these viewed the relationship with one's parents as crucial, in some way, to determining SSA. The problem with these theories, as with much psychoanalytic theorising, is in finding the empirical data to support them. 
So what is the epidemiological evidence relating to early life experience and SSA? As we have noted, there is some evidence for a birth order effect, although we do not know whether this mediates a biological or social influence. Either way it is probably not a very large effect. There are some replicated findings of greater instability in the early life experience of people with adult SSA, [21-23] especially in terms of parental relationships. But the overall contribution may not be especially strong; it is difficult to construct a highly specified psychosocial developmental model for the 'causation' of SSA on the basis of current evidence.
These uncertainties, on both biological and psychological fronts, are not confined to our understanding of human sexuality. They apply to most complex human behaviours. The evidence, for the role of family dynamics in the development of personality in general, is notoriously complicated. What factors, for example, lead people to make certain career choices? Biological factors will play a significant role (contributing to intelligence and temperament). But a variety of family and cultural experiences, as well as different role models we encounter, are likely to mould and shape our career choices. Different patterns of interaction between these factors will be crucial, and personal choice will play a part at numerous points across this developmental trajectory. It is likely that sexual desires and attractions are moulded in similar ways, with biologically determined differences of temperament and personality interacting with the familial and social environment as well as with personal choice. At present, we simply do not have the epidemiological tools to unravel the detail of all this.
Clearly some people can. We have already quoted anecdotal evidence from somebody who changed on her path through feminism. There are numerous examples. But can anybody with SSA change if they want to? And are the ex-gay programmes run by some Christian organisations effective or are they likely to do more harm than good?
This catapults us into the eye of a storm. Some people claim remarkable stories of change whilst others report disastrous accounts of harm and abuse. There are anecdotes on all sides; some people claim that this kind of ministry and counselling approach are fundamentally unethical.
Recently, there have been two studies on this issue in the USA, one by Robert Spitzer, a psychiatrist; another by Jones and Yarhouse, psychologists.  Both studies conclude that some people can change as a result of participation in various ex-gay programmes and pastoral or counselling ministries. Because of the methodological problems, however, the authors are rightly reluctant to estimate the size of any effect.
Whilst we do not have space to critique these studies in detail, we need to note that it is difficult to carry out high quality research in this area. Indeed, there is little robust evidence of efficacy for the various 'gay affirming' counselling and therapy approaches either (although they continue to be widely commended by those on the other side of this debate) and we have to be careful about applying double standards. Most studies suffer from weaknesses in the way that subjects have been identified and the methods used to measure change. Studies also tend to group the many different types of interventions together when they range from psychological techniques delivered by professionals, through various ex-gay ministry approaches, to informal prayer and support offered by ministers and lay people.
But do ex-gay programmes harm people? One study  has reported significant numbers of people who believe they have been harmed in some way. For example, some became depressed or suicidal and some developed self-esteem problems or severe guilt because they had not achieved hoped for effects. Other reports, [24,25,27] based upon case series of participants, suggest that the proportion may actually be relatively small. But it is difficult to evaluate these conflicting claims because of the methodological problems we discussed earlier. We do not know what proportion of individuals in the wider population with SSA would suffer harm as a result of engaging with one of these interventions because of unknown biases in the way examples of 'harm' were collected. All we can conclude is that some individuals report various types of harm as a result of taking part in these interventions but there is no clear evidence at present to suggest that this is a very common or major outcome.
Professional organisations, including those of psychiatry, psychology, counselling and social work, have expressed varying degrees of reservation about ex-gay counselling. [28,29] We need to pay careful attention to these concerns, especially where they are focused upon the issue that these interventions might be causing harm. Further, we need to be sensitive to the risk that such interventions could lead to further stigmatisation and prejudice toward people with SSA. And nobody should ever feel coerced into seeking help from ex-gay ministries.
However, as we have seen, secular professionals have no special skills in deciding between different value systems. Christians may also have legitimate concerns about the extent to which secular professionals adequately recognise and respect the religious values of their clients when they issue these statements. Whilst some professionals do acknowledge that religious values are important,  all secular professionals need to recognise that individuals have a right to decide that their religious identity is the preferred organising framework for their mental life. We need to protect the individual's right to bring his or her feelings and behaviour into line with his or her religious and moral values, rather than the other way around – if that is their choice. This right should be defended even when it means learning to live with sexual feelings that the individual may not value and may not wish to nurture.
So how should we approach these various ex-gay ministries and therapy approaches? At present there is insufficient objective and reliable evidence of harm to justify a general prohibition of religiously motivated programmes to support people with unwanted SSA. And there is evidence that some people with unwanted SSA can achieve significant change and others can achieve satisfaction in managing their attractions more satisfactorily in line with their religious values. However, reports of harm and poor standards of practice call for a number of safeguards. Organisations and ministries offering support to people with SSA need to adhere to clear and robust guidelines  that ensure participants give detailed informed consent. These must address issues of the supervision, training and audit of those who get involved with offering these different forms of support. Estimates of the likelihood of 'change' (in terms of achieving full heterosexual functioning) should be conservative and there must be clear recognition of the potential for harm where expectations are unrealistic. Guidelines must ensure that nobody feels coerced into these programmes by their parents or anybody else.
With these safeguards in place, people have the right to choose for themselves how they want to manage SSA within the framework of their religious values. Some may decide to change their values and beliefs to bring them into line with their attractions, possibly seeking out some kind of gay-affirming counselling or support. Others may decide to bring their feelings and desires into line with their religious convictions, holding to the teaching of the Bible and the traditional teachings of the Church. Some people may decide to explore the possibility of change through participation in forms of counselling or pastoral ministry. Others may prefer to make a commitment to pursue a celibate lifestyle by relying upon the informal support of friends, their faith and the presence of the Holy Spirit in their lives.
This is a complicated debate that often generates more heat than light. We have seen that we need to steer clear of asking scientists and psychologists to answer questions that they are not equipped to answer. Whilst neuroscientists, psychiatrists and psychologists have much to teach us, they are ill-equipped to help us understand what the Bible [32,33] is actually teaching on this matter. Questions about the divine intention for the ordering of human relationships are theological and ethical issues, for which science and psychiatry have no answers.