Social science has a lot to say about “homosexual marriage”. It shows marriage and same-sex union originate differently and should not be equivalent, either in concept or law.
Many family factors have a bearing on later same-sex union, but in the study I cover here, it is the heterosexual family in breakdown/need that has most effect.
I take this stance from the results of a huge study of two million Danes published in 2006 by an epidemiological expert, M. Frisch, working in Copenhagen. The large number of subjects means a very representative sample, and unprecedented statistical reliability of findings. The study shows what correlates with entering marriage, and what correlates with same-sex union.
Gay “marriage” has been legal in Denmark since 1989.
Factors increasing the likelihood of same-sex unions:
For men: Older mothers, divorced parents, absent fathers and being the youngest child.
For women: Maternal death during adolescence, and being the only or youngest child or only girl.
For men with mothers over 35 years of age there was a 34 per cent greater likelihood of same-sex union. But this effect did not exist for women.

United States couple Megan Ward and Bryce Horsley smile after lighting a unity candle during their wedding. Research suggests that about five factors predispose children towards homosexual marriage when they reach adulthood.

If women lost their mothers between the ages of 12 and 17, the chance of a same-sex union was 93 per cent higher, one of the largest effects in the survey. Children whose parents divorced after less than six years of marriage, were respectively 34 per cent and 26 per cent more likely to enter same-sex unions.
If parents divorced before a child’s sixth birthday, the child was 39 per cent more likely to enter a same-sex union. If men left cohabiting/married parents before the age of 18, there was a 55-76 per cent higher rate of same-sex union, again a rather large effect. (This could, however, be a result of finding the family situation difficult or discovering same-sex attraction in oneself, making home life problematic.)
For women, same-sex union was 12.7 per cent less likely with each older sister. The more younger siblings a child had, the less likely there would be a later same-sex relationship: for men, 9.2 per cent for each younger sibling; for women, 13.7 per cent. The youngest siblings of both sexes were much more likely to marry heterosexually than enter same-sex union. Number of siblings affected willingness to marry!
“Our findings strongly suggest that siblings were influential in subsequent marital choices. Although effects were modest for most sibling factors, they differed between heterosexual and homosexual marriages.” (Frisch and Hviid, Archives of Sexual Behaviour.)
Factors increasing the likelihood of heterosexual marriage:
As with all such studies, the effects are weak-to-modest for individual factors. But here are factors that increased the chance of a heterosexual marriage:
Young parents; small age differences between parents; stable parental relationships; many brothers and sisters; and late birth order (The fact that late birth order increases the chances of both heterosexual marriage and same-sex union is discussed in a separate section of this article).
This survey effectively says that if you want to perpetuate the state of marriage for which the Church and other institutions have laboured long, marry fairly young, to someone close to your age, and make your intact marriage a very, very high priority. Large intact families will lead to large intact families; but small and unstable families will tend to die out.
The birth order effect means that if you are the baby of the family, you are not disadvantaged by your large family and you want to be in a similar family yourself. Other research shows you are also mostly biologically advantaged, having fewer physical and mental problems.
Factors lowering the likelihood of heterosexual marriage:
Those “less likely to marry” were much more likely to form de facto heterosexual relationships.
Men with unknown fathers were 21 per cent less likely to marry, women 16 per cent less. Indeed, why try to copy what you have not experienced yourself? Children of older fathers (compared with 20-year-old fathers) were 18 per cent less likely to marry.
The age gap between parents mattered. If the mother was older than the father, or the father was more than five years older than the mother, children married at significantly lower rates. Death of a parent while you were still in childhood or adolescence produced 5-6 per cent lower marriage rates, a small, but real, effect.
Divorce had significant effects, particularly for male children. The effect was worse the earlier the divorce, and made children’s marriage as much as 25 per cent less likely (but same-sex union as much as 40 per cent more likely). For women, the corresponding figures were 15 per cent less for marriage (but nearly 40 per cent more for same-sex union). Interestingly, if parents never formally married, the percentages were very similar. Cohabiting can produce in children about the same bad effects as divorce!
The authors said: “Whatever ingredients determine a person’s sexual preferences and marital choices, our population-based study shows that parental interactions are important.”
An even more recent survey (Högnäs, R. & Carlson, M., 2012, Social Science Research), the first of its kind, shows that if children are born to parents not married at the time, then those children are 48 per cent more likely to produce their first child without formal marriage — a risk that has been increasing over the last several decades. This means that traditional heterosexual marriage is unravelling, and at an increasing rate, in the Western world.
Birth Order:
The birth order effect is an odd one. Late birth order increases the likelihood of both heterosexual and homosexual unions. But one of the most striking and controversial results of Frish and Hviid’s very large and well controlled study was that it found no birth order effect (effect of elder brothers) for same-sex attracted men. Some Canadian authors have claimed to have found that the rate of male homosexuality increases by about 30 per cent for each older brother, and theorise this is due to biological factors. My own theory is if family relationships are good enough the youngest child has a positive experience of family — reinforcing the desirability of family — but if not, the weight of it falls on the weakest member, for example, breakdown in good masculine modelling can leave a boy looking for affection and acceptance in the arms of other males.
Deficits in family life lead to fewer stable marriages, less future marriage and more same-sex union. Same-sex union that has come from disintegrating family life cannot perpetuate it. Unstable at the root, it tends to produce insecure children and further instability. It is headed in a different direction from social and national wholeness.
The survey shows that heterosexual marriage tends to reproduce both its members and social circumstances, but a public comparison like this will probably become targeted under the new legislation if anyone claims to be offended, and makes a complaint to the Human Rights Commission, so listen to the science now — it might be your last chance!
— Neil E. Whitehead (PhD) has had a varied career in research with the New Zealand Government, United Nations, and Japanese universities. He is the author of 150 research publications, including 15 on subjects related to this article.