Petter (petter_haggholm) wrote,

“The G-spot 'doesn't appear to exist', say researchers”; “How do you figure?”, say I

An article I recently read boldly claims that The G-spot 'doesn't appear to exist', say researchers. I read this with a sigh, as I know from experience how greatly distorted any research findings can get when they are published in mainstream media. Clearly, this was an instance of such distortion. I was curious to see what the actual study said, and went off to find it. You may read it here, if you are curious.

Sadly, it wasn’t very distorted after all.

In fact, the press release from the Department of Twin Research & Genetic Epidemiology was worse than the articles I had read. It presents the following conclusion from their study:

The complete absence of genetic contribution to the G-Spot, an allegedly highly sensitive area in the anterior wall of the vagina which when stimulated produces powerful orgasm, casts serious doubt on its existence, suggests a study by the Department of Twin Research to be published in the Journal of Sexual Medicine.

The investigators carried out this study by recruiting 1804 female volunteers from the TwinsUK registry aged 23-83 years. All completed questionnaires detailing their general sexual behavior and functioning, and a specific question on self-perception of the G- Spot. The researchers found no evidence for a genetic basis. This led to the conclusion that – given that all anatomical and physiological traits studied so far have been shown to be at least partially influenced by genes – the G-Spot does not exist and is more a fiction created by other factors e.g. an individual’s own sexual and relationship satisfaction or self-report is an inadequate way to assess the G-Spot and researchers should in future focus more on ultrasound studies.

The impression I took from the mainstream press articles, and which was reinforced by the institute’s press release, was that the existence of the G-spot was inferred to correspond to study participants’ reports of whether they had one. If this were so—if we could determine anatomy by poll—I expect I could find some people with more spleens than kidneys and more livers than lymph nodes.

I took the trouble to read the actual paper (it’s fairly short and quite accessible). The reality turns out not to be quite so bad. The main point—well, let me make an aside here and say that I find it extremely odd that what seemed to be the main point emphasised in the paper was considerably de-emphasised in the press release and consequent mainstream articles, seriously reducing their credibility. Anyway, back to the point:

The main point of the paper is that if the G-spot exists, it is an anatomical structure; if it is an anatomical structure, it is presumably genetically inherited. Even if some women have it while some don’t, we expect to find a strong correlation in twins. Since heterozygotic twins share 50% of their genome, and monozygotic (‘identical’) twins share 100% of their genome, if it’s genetically heritable at all, we should see a correlation in twins, especially monozygotic ones: If one twin has it, the other should (more often than is the case with unrelated people); if one twin does not, the other shouldn’t. Because twins are typically raised in extremely similar environments, even environmental factors should be similar. In particular, monozygotic twins should be more similar to each other than heterozygotic twins for heritable (but not environmental) factors.

Well, this turned out not to be the case: Heterozygous twins report that they have G-spots about as often as do monozygous twins, and this is the real point of the paper. It’s not as spectacular as the mainstream news articles, but I’m surprised that they so failed to emphasise this in their own press release. Ah well, such is the hunt for fame, I suppose.

In the conclusion of the real, scientific paper, the authors are of course forced to admit that

A possible explanation for the lack of heritability may be that women differ in their ability to detect their own (true) G-spots.

They, of course, do not believe this to be the case. We may reasonably ask, why not? And how good is your evidence? My thoughts will be very tentative, because I’m not an expert in any related field; but we may at least reason about it.

First, I will note that the study’s exclusion criteria were, at times, a bit puzzling.

Women who reported that they were homo- or bisexual were excluded from the study because of the common use of digital stimulation among these women, which may bias the results.

I daresay it may bias them! For example, if the G-spot exists, it’s a specific anatomical location inside the vagina. Because it is postulated to be a very specific location, it may be difficult to stimulate with the penis, which is after all not prehensile and may not be angled so as to optimally stimulate a specific location. This postulated spot could perhaps be more easily located and stimulated with the fingers. Therefore, if it does exist, and if we are restricted to self-reporting as evidence, I would expect to find much stronger evidence for this in a population with common use of digital stimulation. The people I would ask first are the people whose answers they discarded. I would be very curious to see how their data are affected if they include this population. What was their rationale for the exclusion criterion? Was it determined beforehand, or after the data were in? Would it contradict their conclusion? What if this population were considered exclusively?

This looks like a very serious weakness to me, as the exclusion criterion seems to be specifically geared towards reaching a particular conclusion. (I can’t think of anything much more damning I could possibly say about a study.) It’s not the only thing that makes me raise an eyebrow, though (but it is the strongest).

Another thing is that, well, some traits just aren’t very heritable. (This is why we measure heritability; if there weren’t variation in how strongly phenotypic traits are associated with genes, there’d be no need.) I suppose the authors may reasonably expect their readership to be familiar with not just the concept of heritability (as I am), but also what kind of numbers we should expect (as I am not). Is a “close to 0” heritability common, or unusual, or rare, or impossible in variable phenotypic traits? Still, it is possible that heritability of the G-spot—not necessarily its existence, but perhaps its precise location and orientation, or its sensitivity—is relatively low. Is the study still powered to detect it? How does this render it more vulnerable to other confounders?

There are various criticisms leveraged against twin studies in general. Twin studies are potentially wonderful tools because monozygotic twins offer unique opportunities to investigate heritability. (Personally, I think the most interesting ones are of that rarity of rarities, pairs of monozygotic twins raised apart; the surprising similarities they show in a very wide range of behavioural traits is strong evidence of genetic conditioning.) But they are not perfect.

And finally, I make the observation that the institute—the Department of Twin Research & Genetic Epidemiology—maintain a database of twins (an awful lot of them: Some 11,000 people). This is great; it enables them to efficiently perform twin studies. However, studying the same sample over and over again is problematic. If you look at the same N people, examining them for different properties over and over again, you’re bound to find an apparent correlation eventually. Think about it: If you pick 100 names at random from a phone book, you’ll expect about half of them to be male, half female; and about 8–15 of them to be left-handed…but if you examined them for blood pressure, and dietary habits, and sexual preferences, and number of children, and so on for any number of questions, it would be bizarre if they were an average sample in every respect. This is a problem with data mining. Clearly, the department’s database is pretty large, but then they’ve already published over 400 research papers. At what number of papers should we statistically expect to find spurious calculations?

All in all, the study was a bit more sensible than mainstream media had me thinking at first, but as research papers go, I found it surprisingly unimpressive. In particular, the exclusion criterion that discarded answers from gay and bisexual women smells very fishy, and I wouldn’t be terribly surprised if it “biased” the results so far as to invalidate their conclusion.

In a general sense, I trust science—I trust the scientific method, and (to a lesser but considerable degree) I trust that scientific consensus will move toward the right answers: Science is often characterised as an asymptotic approach to the truth (we may never know it exactly, but we will get ever closer). However, when considering a single study, one should be cautious. Never trust what the mainstream press says about it at all, whether you like what it says or not—ordinary reporters lack scientific savvy, good science reporters are rare, and after the editors have their say, it’s often dubious whether the scientists behind a finding would agree with anything the press has to say about them except, perhaps, the scientists’ names.

And while the scientific method is excellent, and the scientific consensus is the best approach we have to knowledge, some studies just aren’t worth the paper of the webpages they’re published on. If you want to adjust your opinions according to a single study, read it. Read it critically.

Tags: medicine, science, skepticism
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