Wednesday, May 11, 2005

More on biological v. genetic causes

Mark Kleiman highlights the "biological = innate" confusion when he writes about the pheromone study I commented on yesterday, "if the laboratory result holds up, the argument that the sexual orientations of males are hard-wired, rather than chosen, just got much stronger." In fact, "hard-wired" and "chosen" are perfectly compatible - any choice you make will naturally be reflected in the wiring (or some other biological aspect) of your brain. The mere fact that homosexuality has a neurobiological basis tells us very little about whether homosexuality is innate, learned, involuntary, or chosen.

Rather than looking to biological evidence for the innateness of homosexuality (which will be found not in the biology of adult brains, but in genes and possibly the biology of fetal and infant brains), we should look instead to the actual experiences of gay people - the vast majority of whom say that they didn't choose to be gay. Isn't that enough?


Anonymous Anonymous said...

I've seen this problem all over the public discussion of the causes of homosexuality, too. For the most part, the researchers seem to be a little more discerning in the literature. The "innate" vs "biological" distinction is made when causes are discussed (innate causes are biological, of course, but the way the conditional relationship works, to assume innateness from "biological" would be to commit the fallacy of affirming the consequent).

I'm not sure we should treat the experience of gay people as sufficient here, but that's because I'm not sure we should treat anyone's introspective experience as sufficient to answer such questions. However, I am quite sure that, despite the attention both positive and negative, from both supporters and anti-gay bigots, to the issue (it appears that neither side is willing to accept any evidence of innateness as definitive, no matter how many twin studies - and there are plenty - show a heritability rate of around .5), the innateness of homosexuality is politically and socially irrelevant. Regardless of where homosexuality lies on the rather long continuum between choice and complete genetic determination, we should treat gay people with the same amount of respect and tolerance. 

Posted by Chris

5/11/2005 05:01:00 PM  
Anonymous Anonymous said...

the innateness of homosexuality is politically and socially irrelevant. Regardless of where homosexuality lies on the rather long continuum between choice and complete genetic determination, we should treat gay people with the same amount of respect and tolerance. 

I agree completely. I wish people would stop acting as if the innateness of homosexuality had any bearing on its valence - if homosexuality really were a bad thing, then it would be either a voluntary sin (so we'd be justified in condemning and banning it and punishing gay people for choosing a "sinful lifestyle") or some terrible, though involuntary, illness or disorder (and we'd still be justified doing horrible things like trying to "cure" it, send gay people packing off to an insane asylum, and so on). Really we should be arguing against the idea that homosexuality is bad, per se. 

Posted by Andrew

5/12/2005 05:49:00 PM  
Anonymous Anonymous said...


I agree with you that these studies, while certainly interesting, are beside the point they so often seem intended to make: that sexual orientation is "natural" and therefore somehow benign. Whether one sexual inclination is benign and another isn't just can't be answered by neurological investigations.

But I have two even bigger  problems with such studies:

(i) are their findings invariant? If so, say so. If not, attempt to explain why those subjects whose hypothalamuses reacted in sex-typical (or, in the case of heterosexual subjects sex-atypical) ways did so. Just how contributory to sexual orientation are variations in the hypothalamus? Sufficient? Or just necessary? Or neither? Feigning that there were invariant results in this (apparently small) pheromone study--as at least Savic's abstract does by omission and the giddy Times piece does by direct implication--smells of junk science.

(ii) who, exactly, is "heterosexual" and who, exactly, is "homosexual"? Speaking as a gay male myself, I can testify that a great many married and otherwise habitually heterosexual men sleep with other men in various circumstances. (One STD study, reported in Newsweek, of homosexual activity in India put the number at around 30% of the male population! I suspect something must have been screwy there. But you never know.) Is Savic really investigating homosexuality and heterosexuality--or merely their most extreme Western manifestations? I assume Savic employed some sort of Kinsey scale--but I submit that a sizable percentage, if not a majority, of homosexuals and bisexuals (still) don't self-identify as such. If so, there's no reliably inclusive sample of "homosexuals" or "heterosexuals" available for testing. Certainly the carefree homosexuals happy to participate in such studies are unrepresentative of their orientation in fundamental respects. There's quite a bit of anecdotal evidence, for example, suggesting that the more "out" a homosexual male is, the more effeminate he's likely to be--possibly because he doesn't have much choice in the matter. (Are studies like Savic's, in other words, merely investigating a subpopulation of effeminate homosexuals and then sloppily extrapolating those results to homosexuals as a whole? A wider population whose hypothalamuses may well respond far more sex-typically?) Such obvious questions rarely seem to occur even to those studying the subject in depth.

These studies, and not just the tabloidish way they're so often publicized, begin with assumptions so dichotomized and reductive of human sexuality that I judge them worse than trivial: I think they're tantamount to phrenology.  

Posted by dan

5/13/2005 02:13:00 PM  
Anonymous Anonymous said...

the vast majority of whom say that they didn't choose to be gay. Isn't that enough? 

of course not! all people in prison are innocent remember.

in any case, i have been hearing that the concordance figure is closer to 0.25 as opposed to 0.50 according to the "best" current numbers...the earlier research had some sampling bias errors. nevertheless, that just tells us how "heritable" homosexuality is...there of course could be developmental/epigenetic issues at work here explaining most of the variation in expressed and actualized male homosexuality (that's my suspicion). this studies need to work themselves out in their own time.

p.s. my friend chandler burr wrote a book about the biology of homosexuality (he's gay personally). it was funny/strange that he was attacked for being a homophobe by some people for making this connection. and of course the religious right wasn't a big fan of his book either. 

Posted by razib

5/13/2005 03:00:00 PM  
Anonymous Anonymous said...


On point (i): I haven't had time to look at the data in detail, but here's my best guess - I'm sure the findings weren't completely invariant, but I imagine that there was some sort of distribution for each category, but despite the variation the difference between the two groups was still statistically significant.

I think it's a little unfair to accuse them of leaving a false impression of invariance in the abstract - it's fairly standard practice to state the broad conclusions in the abstract and then provide the details of standard deviation and so on in the results section. As for Nick Wade's article, he could have made a mention of variance, but there's little point in confusing a lay reader with talk about t-tests, standard error of the mean, and so on...

On (ii) - the article says the researchers used the Kinsey scale and picked only 0's and 6's for males. So, yes, this leaves out a huge range of human sexuality. But - it's often so hard to get a good statistical signal in these brain imaging studies that you want to pick out extremes at first. I think a good follow-up study would be to take subjects everywhere along the Kinsey scale, and then see if there was a correlation  between activation of the hypothalamus and placement along the Kinsey scale. This will of course be muddied by people being in the closet, subject self-selection, imprecision of the Kinsey scale, the fact that the Kinsey scale is a product of a particularly Western conception of sexuality and may not apply universally, and so on. But science is never perfect and you take what you can get - with however large a grain of salt you need.

In any case, as I said in my previous post, the real scientific significance of this study is not in the "biological basis of homosexuality" bit, but in the further support of the hypothesis that AND and EST are human pheromones. 

Posted by Andrew

5/14/2005 11:51:00 AM  
Anonymous Anonymous said...

there of course could be developmental/epigenetic issues at work here 

Yes, I think that's definitely the case. You probably know about the studies where men who have more older brothers are more likely to be gay, and the hypothesis that mothers develop antigens against fetal male hormones so that later sons get less exposure to those hormones... Who knows if that's really the case, but it's an interesting idea! 

Posted by Andrew

5/14/2005 11:57:00 AM  
Anonymous Anonymous said...


The notion that there's "no point in confusing lay readers" with accurate information just underlines what bugs me so much about the way these studies are produced and publicized. 99% of the human population will never read Savic's paper, or its (one can hope) detailed sample descriptions, its statistical breakdowns, its nontrivial mean deviations, etc. And much of the scientific community clearly has a vested interest in that remaining the case--otherwise they'd make such tendentious papers more widely accessible more often. (I just noticed one skimpy little journal letter dealing with sex being offered to the unwashed for no less than a hundred bucks. Please! This is the Internet age, people.)

In the absence of accessibility, researchers who publish papers in particularly controversial areas bear an extra burden of explication when summarizing their findings. That burden doesn't, by the way, require boring readers unto death with mathematical and statistical jargon: it merely requires giving notice in summary that few or some or many of the subjects in study X responded in Y way, while others responded differently. A quick disclosure of that kind, repeated often enough, discourages casual readers from leaping to the unwarranted over-generalizations that nearly all human beings find so damned attractive.

Examples of abstracts summarizing controversial findings which actually do bother to include such simple qualifications up front include the summary of McKnight and Malcolm's "Is homosexuality maternally linked?" in which they duly note that: "...the first two tests were not supported and only partial support was found for the third proposition." And the summary of Rahman et al's "Performance Differences Between Adult Heterosexual and Homosexual Men on the Digit-Symbol Substitution Subtest of the WAIS-R"  in which they note: "The magnitude of these differences were modest by standard criteria." And so on. The more provocative the subject matter, the more disclosure of even marginal deviations should be preferred.

Savic's pheromone paper's abstract, by contrast (and it certainly isn't alone in this), glibly leaves the impression that straight men whose hypothalamuses don't sufficiently react to female sweat are likely latent homosexuals, while gay men whose hypothalamuses remain mysteriously unmoved by male B.O. likely aren't sufficiently homosexual. That, of course, is the flip side of intimating--as this study does by carelessness or design--that all male homosexuals respond to same/opposite sex sweat in X fashion and all heterosexual males respond in some contrary fashion. Nowhere that I noticed in that NYT piece does Savic make any effort whatever to discourage casual readers from assuming something so preposterous--and so seductively reductive.

The mere fact that "a huge range of human sexuality" was evidently left out of Savic's study suggests that its findings--which, as I've said, are certainly interesting in a severely circumscribed context--say nothing definitive about "most" of anybody vis-a-vis their sexual proclivities.

Even regarding the comparatively minor question of pheromones themselves (a question I'm sure Savic herself wouldn't consider trivial, as it seems to be her favored field of study) and their contribution to human sexual arousal, this study offers nothing notable: obviously pheromones, or their lack, neither prevent nor inspire human sexual response in any meaningful way. People with nasal congestion do, after all, still get turned on by whatever turns them on. (And, as I understand it, the pungent concentration of pheromones employed in Savic's study was far more potent than anything found outside the lab.) Yes, that Homo sapiens retain a mild vestigial receptivity to sex aromas is interesting. But then so is the fact that we retain tail bones.

For myself (and like you, I assume) I'm very impressed with the accumulating evidence of gonadal steroids in utero as a contributory factor in producing exclusive male (and perhaps even female) homosexuality. (Along with fluid developmental and cultural inputs still far too chaotic to categorize.)

Then again, male homosexuality has lately been loosely correlated with everything from fraternal birth order, to hypermasculine cochleas, to left-handedness, to second and fourth finger asymmetries, to exceptionally impressive cocks.

As I said above: were still at the phrenological stage in exploring the heritable and/or prenatal components of our myriad sexualities. Which is why anything pretending to say anything definitive on the subject at this early date tends to leave me cold.  

Posted by dan

5/15/2005 08:24:00 AM  
Anonymous Anonymous said...

otherwise they'd make such tendentious papers more widely accessible more often. 

I'll respond more fully in a bit... but just on this point, actually the Proceedings of the National Academy of Sciences (which is where the Savic article was published) are freely available online, as far as I know. (The Savic article itself is not yet, I think because it hasn't been published in print yet. But it should be soon.) 

Posted by Andrew

5/15/2005 10:37:00 AM  
Anonymous Anonymous said...

True enough. The Public Library of Science is also ahead of its time in this area. Still, those sites and a few others remain exceptions to a prophylactic rule. Firewalls and secure logins abound. There may be some perfectly valid reasons for this exclusivity (like, say, money), but it's a serious pain in the ass for anyone unaffiliated with participating universities and institutions. God only knows how many times I've slammed into such barriers myself.

In any event, I suspect that simply noting in the summaries of particularly controversial studies that all studied Xs and Ys didn't react in interesting way Z--assuming that's the case--would go a long way toward educating reporters and their readers about the provisional nature of science--and discouraging reflexive overgeneralizations. 

Posted by dan

5/15/2005 10:04:00 PM  
Anonymous Anonymous said...

I may have praised PNAS too soon. Just linked over to their site and noticed that Savic's paper apparently is available: for either $10, $25 (granting full access to PNAS for seven halcyon days), or a subscription. Jeesh... 

Posted by dan

5/15/2005 10:25:00 PM  
Anonymous Anonymous said...

It turns out that PNAS is only freely available after 6 months . But that seems like a fairly reasonable compromise between making science freely available and letting journals cover the cost of publication and supporting their parent organizations. I believe last summer Congress proposed requiring all NIH-funded research to be published in freely available journals or something - don't know what happened to that proposal, but this kind of "free after 6 months" compromise is workable.

I agree that it is annoying when you find an interesting abstract and cannot access the article unless you pay some ridiculous fee... even my university doesn't have them all...

The more provocative the subject matter, the more disclosure of even marginal deviations should be preferred. 

That's an interesting criterion. The data typically generated in my area of research has an absolutely appalling degree of variation, even though when you push the sample size high enough you can reach statistical significance. But no one ever says so in the abstract, and I suspect no one cares because, sadly enough, few laypeople really care about my research and the only people who do care are other people who do similar experiments and also know about the infuriatingly variable results. I guess my point is that all of science has these caveats though, as you say, the duty to be scrupulous is more strict the higher the chance of being misunderstood.

One possibility which has just occurred to me is that Savic takes the variability inherent in all brain imaging studies to be so common-sensical, so obvious (to her) that she didn't bother mentioning it to the reporter (in the same way that if I were talking about my research, I wouldn't mention it unless asked). Science writers and scientists always argue about who has the responsibility to ask questions or provide answers, but I think in this case Nick Wade could have made the extra effort.

Random anecdote about brain imaging studies: I once did an fMRI study, got paid my $50, and then was called back a couple weeks later, when they offered me more money to get me to come in again - because my brain "scanned well." I took that to mean that it gave them good results - but whether that means "nice, relatively noise-free results" or "the results they were expecting" is one of those tricky things about science... 

Posted by Andrew

5/16/2005 08:48:00 AM  
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