The referendum on marriage equality scheduled to take place in 2015 will be a historic moment in Ireland.

With more than 73 per cent of citizens currently in favour of enshrining such an amendment in the Constitution, it seems almost unfathomable that homosexual acts were a criminal matter here a mere two decades ago. Despite the high degree of support, there is still bitter opposition to gay marriage, and misunderstandings abound.

From the perspective of traditional Catholic doctrine, homosexuality is “ordered towards an intrinsic moral evil”, and is considered a deeply unnatural state of being – peccatum contra naturam.

Not only is this a classic example of the naturalistic fallacy, it also spectacularly fails to stand up if one takes even a cursory glance at the natural world; homosexual behaviour is ubiquitous in the animal kingdom and has been documented in more than 1,500 species, from giraffes to elephants to dolphins and our primate cousins.



Homosexual pairings

While much of this sexual activity is non-exclusive (activity with the opposite sex is also found), exclusively homosexual pairings do occur – to cite one common example, about 8 per cent of domestic rams will form partnerships only with other males and cannot be enticed into mating with ewes. The proclivities that are to be found in the natural world are entirely relevant to us, for in spite of the lofty status we assign ourselves, we too are part of the animal kingdom, differing only in that we have a prefrontal cortex evolved enough to give us the meta-cognition to be aware of that.

There is the equally fallacious belief that homosexuality is a choice, but the vast majority of the scientific evidence suggests that this is erroneous; current best evidence indicates that while sexual orientation is a complex affair, it is predominantly biological in basis, related to the interplay of genetics, brain structure and prenatal hormonal factors.

Viewed in this light, the oft-asserted canard that sexuality is a “lifestyle choice” makes about as much sense as arguing a person has chosen their eye colour.

Despite the insinuations of conservative groups, homosexuality itself is not psychologically unhealthy – while non-heterosexual youths suffer proportionally higher depression rates than their heterosexual counterparts, this difference is correlated heavily to homophobic treatment by peers, and even more so, parental disapproval.

A 2009 study by Ryan et al in the journal Pediatrics found that children who experienced a high level of parental rejection of their sexuality were six times more likely to be depressed and eight times more likely to have attempted suicide than youths whose sexuality was accepted by their parents.



‘Defending marriage’

“Defence of marriage” arguments also ring resoundingly hollow .

If two people who love each other choose to enter into a marriage, this has absolutely no bearing on anyone else’s marriage. Allowing homosexuals to marry is not going to invalidate conventional marriages, or change their status whatsoever.

The related argument that marriage is exclusively about procreation is astoundingly archaic – following such logic to its conclusion, infertile or elderly couples should also be denied the right to marry.

Such vapid arguments are mere sound and fury, deliberately ignoring the fact that homosexuality is a natural variation in sexual orientation that has been with us since we took our first tentative steps as a species.

Denying homosexuals the rights that are accorded to heterosexuals is not defending marriage or children, it is barefaced discrimination and no amount of oratorical dexterity or false expressions of concern can get over that.



Dr David Robert Grimes (@drg1985) is a science writer and physicist at Oxford University. He blogs at davidrobertgrimes.com