ST Review: Gays and biology: Who is right, PM or the MP? (Oct 27)

Oct 27, 2007
Gays and biology: Who is right, PM or the MP?
By Andy Ho

IN THE parliamentary debate over the continued criminalisation of gay sodomy, MP Lim Biow Chuan (Marine Parade) disagreed with Prime Minister Lee Hsien Loong who said that growing scientific evidence shows homosexuality is substantially inborn.

What does the research say? To me, there are four big items that are not what they seem to be.

# First, twins are not what they seem to be. Identical twins share the same genetic make-up while non-identical twins share only half of that, so if the former show a higher similarity in rates of gays, that would suggest a genetic component in homosexuality.

According to some doctors, previous studies of identical twins suggest that 30-60 per cent of the incidence of gayness can be attributed to genetics.

Indeed, many such studies up to the early 1990s indeed suggested so. An Australian study published even in 2000 gave figures in the same ballpark.

Hoewever, many twin studies are methodologically flawed. For one thing, a social phenomenon as complex as gay behaviour is usually reduced to a single item asking the respondent to self-identify as straight, gay or bisexual. Thus, elements of gayness - like sexual fantasy, attraction and behaviour - are not captured carefully in such studies.

For another thing, participants are usually recruited through either twin registries or gay publications, so there is self-selection bias. In the former case, twins who are more like one another tend to respond more frequently to such studies. In the latter case, gay twins - who use such media - must be much more likely to be respondents than non-gay ones.

Thus, most twin studies might start off with a higher proportion of gay twins than a survey of the population at large. When a study of the latter type was indeed carried out in 2002 by Yale and Columbia researchers, they found 6.7 per cent of identical twins to be gay, 7.2 per cent of non-identical twins and 5.6 per cent of true siblings in general.

They concluded: 'Clearly, the observed...rates do not correspond to degrees of genetic similarity. (If) homosexuality has a genetic component, it is massively overwhelmed by other factors.'

# Secondly, families are not what they seem to be. Family studies show gay men tend to have a greater number of older brothers - but not higher numbers of older sisters, younger brothers or younger sisters - than straight men.

Since the environmental influence of more males at home has been shown to not likely cause homosexuality in younger male siblings, it is inferred that this relationship must have arisen from things that happened to male foetuses while they were in their mothers' wombs.

The foetus cannot 'know' its own birth order, only the mother knows it, and, apart from her mind, only her immune system has memory for that. So perhaps a male foetus presents male antigens to its mother's immune system which develops antibodies to such proteins. Thus the more male babies a mother bears, the more of such antibodies she develops, which may then attack the brain of a subsequent male foetus, perhaps impairing its masculinisation.

In such a scenario, however, the genitalia, especially the testes, should logically bear the brunt of an immune attack by the mother's antibodies, but there is no evidence for this in gays. Moreover, most late birth order males aren't gay even when an elder brother is.

Also, the brains in male and female babies are similar at birth, with gender differences in their brains developing only after birth when such an immune attack, if any, is no longer occurring. In addition, foetuses that die in the mother's womb resulting in miscarriages - presumably due to immune attacks - are more often female than male.

Interestingly, too, there are no published studies of attempts to demonstrate such antibodies in mothers with one or more gay sons. No clinical manifestations of such antibodies have been identified as well.

A side note on families: Studies from the early 1990s showed that gays also tend to have a gay maternal uncle. This suggested possible genetic factors transmitted through the X-chromosome. (Females are XX and males are XY).

Specifically, the Xq28 region on the X-chromosome was thought to be a 'gay gene' candidate, but the most up-to-date molecular genomics has not been able to confirm this.

# Thirdly, fingers are not what they seem to be. A well-reported story in the media concerns research comparing the lengths of the second and fourth fingers. The ratio is proposed as a measure of how much the male hormone has acted on a gay man as a foetus.

After accounting for height and weight differences, straight men are said to have longer ring fingers than women and gay men. Since 1998, of about 100 studies, some have confirmed the statistical correlation while others have not. In a 2005 review, a University of Texas at Austin group found that while the ratios for gays remained relatively similar across studies, those for straights varied – especially between American and British studies - which then led to differing conclusions across studies. Also, while the ratios were consistent for white homosexuals, they were not so for other ethnicities, including Asians.

It is now known that female hormones (that are physiologically made in the male body from the male hormone) are probably more important than male hormones in the development of bone length in men.

# Finally, brains are not what they seem to be. In the early 1990s, the sizes of some parts of the brain (including the suprachiasmatic nucleus and the anterior commissure) were observed to differ between straights and gays.

(In)famously, English neuroscientist Simon Le Vay - whose gay lover died from Aids in 1990 - published a paper in 1991 showing that gays who died from Aids had a smaller zone in the brain called INAH-3 compared to straight men and was only as large as that in straight women.

INAH-3 (or the third interstitial nuclei of the anterior hypothalamus), known to regulate sexual behaviour in monkeys, is the smallest of the four 'intersitial nuclei' which are only the size of a grain of rice, so measurements are inherently difficult. Yet, Dr Le Vay measured volumes when cell counts (in tiny brain slices) would have been more accurate. His sample size - 19 gay men, 16 supposedly straight men and six supposedly straight women - was also small.

Their incomplete sexual histories were bothersome too. Thus men and women in his sample who had died from Aids and were known to have used drugs intravenously or received blood transfusions were assumed to have contracted the virus in these ways and not gay sex. They were assumed to be straights though they could have been gays as well. Moreover, it is possible that HIV can shrink INAH-3.

Importantly, other scientists - including a 2001 study - have not been able to repeat Dr Le Vay's findings.

Taken together, the evidence for the role of biology in gayness is still not particularly strong yet. Conversely, it cannot be disputed that an individual's lived experience is very important in determining his self-identity and behaviour. Whatever the case, we are far from understanding how gayness arises in men.