cricket

Hi Kind Bud,

Am I misunderstanding the question? I thought the question was how does homosexuality persist, even though it would seem not to be a successful evolutionary strategy?

In what way does left-handedness reduce evolutionary success?

It doesn't affect one's chances of reproduction the way homosexuality presumably does.

Do you mean left-handedness is a "disability" and you wonder how nature selects for it? It's not that big of a deal.

I don't understand the analogy.

Doubting Didymus

WHAT!?! Sweet merciful satan, no! I meant desire to have children. Have children. Wait. Thats no better, er... Rear. Yes, thats it, rear children.

Desire children. Holy Hagfish.

MrDarwin

Researcher Chris McManus has come up with an interesting theory on the genetics of handedness; from <a href="http://www.discover.com/jan_02/featbiology.html" target="_blank">The Biology of Handedness</a>:

pz

I emphatically disagree. What we have instead is a scientific culture that is favoring genetic determinism, and is pushing genes as an answer where the data is lacking.
Reasoning from anecdote isn't a good way to go. I don't see anything in what you've said here that supports a genetic cause for homosexuality at all -- your observations can be just as easily (and I would argue, better) explained by social and cultural factors.
Turn that around: can you provide any evidence for a genetic basis for heterosexuality?

What I find unpersuasive is the lack of replicability of many of these studies; inconsistencies in the explanations; the glibness with which any observation is rallied to support the notion; the glaring pattern of bias in funding and publication for genetically deterministic explanations; the incredibly superficial rationalizations I see in the papers that attempt to support these hypotheses; and the sheer inanity of the extreme reductionism implicit in the idea. We've seen exactly this kind of 'science' before -- it was called phrenology.

Genes don't explain behavior. They can't. Behavior is an emergent property that isn't defined by an enumeration of its constituent parts, any more than architecture can be defined by measuring the dimensions of bricks.

MrDarwin

No, I think what we have is a popular culture--which I blame on the abysmal scientific ignorance of the public in general, and the popular media in particular--that tends to grossly oversimplify and misunderstand how science works (hey! eating broccoli prevents cancer! drinking red wine prevents heart disease!), and doesn't realize that, just because a scientist discovers evidence for a biological (both genetic and non-genetic) basis for diseases or behaviors, does not mean that genes predetermine those diseases or behaviors. In other words, the genes may be necessary but not sufficient. For example, we now know that many diseases have a genetic basis, but there is also a strong influence from diet, lifestyle, etc. A gene may predispose, but not predetermine, you to have a particular disease. We also know that some diseases placed under a single heading, like "cancer", have multiple causes, both genetic and non-genetic. And in all discussions of homosexuality I have tried to stress that the genetic explanation is an overly simplistic one, and that at best there is a genetic predisposition, which is influenced by many, many other things.

And we're back to square one. I'm not going to bother searching for the articles because you've already admitted to being aware of the studies claiming to have such evidence--your claim is that the evidence presented is unpersuasive. But if homosexuality has no genetic basis whatsoever, as you claim, can you cite a single research paper that reaches that conclusion?

So you believe that genes don't explain, and cannot explain, homosexual behavior in fruit flies? Not even partially? Not even in some particular cases?

Then just what do you think genes do? What do you think they can explain? If genes don't, and can't, explain behavior, then how do you explain the behavioral differences between chimpanzees and humans?

cricket

(MrDarwin I have borrowed your Chris McManus quote and put it <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=001790" target="_blank">here.</a>)

Doubting Didymus

I don't understand how social and cultural factors could engender such a strong and irreversible trait. What social factors are likely to do that, exactly? Peer pressure? Widespread acceptance of homosexuality? (!) How do social factors account for the fact that many, if not most, homosexuals claim that they did not choose their predisposition?

MrDarwin

Playing devil's advocate for the moment, just because a characteristic is immutable, or present from birth, does not make it genetic. One theory on homosexuality is that some kind of hormonal or other physiological influence on the fetus, while still in the womb, somehow fixes (or influences) the sexual orientation of that fetus, perhaps by affecting how the brain develops. (I think there's even some merit to this argument, and such a scenario may account for some instances of homosexuality. As I've stressed numerous times, I don't believe there is a single "cause" of homosexuality.)

Doubting Didymus

I understand that, and I do not really have an opinion on whether homosexuality is genetic or not. My question is how purely social factors could engender homosexuality. It appears farfetched to me, so I require more information.

Ta.

ps418

You're absolutely correct, with the proviso that although genes clearly play a role in many behavioral variables, they rarely if ever determine behavior. Its very common for people to confuse genetic influence on behavior -- which is empirically undeniable-- with genetic determination of behavior, which is a different beast altogether, and is not taken seriously by any behavior geneticists. I agree with Bouchard when he says that for "almost every behavioral trait so far investigated . . . an important fraction of the variation among people turns out to be associated with genetic variation. This fact need no longer be subject to debate; rather, it is time instead to consider its implications" (1990, Science 250, p. 227).