Sexual Orientation in Fruit Flies

Today's New York Times has a front page story on recent research into the genetic basis for sexual orientation in fruit flies.  Here's an excerpt:

In a series of experiments, the researchers found that females given the male variant of the gene acted exactly like males in courtship, madly pursuing other females. Males that were artificially given the female version of the gene became more passive and turned their sexual attention to other males.

"We have shown that a single gene in the fruit fly is sufficient to determine all aspects of the flies' sexual orientation and behavior," said the paper's lead author, Dr. Barry Dickson, senior scientist at the Institute of Molecular Biotechnology at the Austrian Academy of Sciences in Vienna. "It's very surprising.

. . .

[E]xperts said they were both awed and shocked by the findings. "The results are so clean and compelling, the whole field of the genetic roots of behavior is moved forward tremendously by this work," said Dr. Michael Weiss, chairman of the department of biochemistry at Case Western Reserve University. "Hopefully this will take the discussion about sexual preferences out of the realm of morality and put it in the realm of science."

He added: "I never chose to be heterosexual; it just happened. But humans are complicated. With the flies we can see in a simple and elegant way how a gene can influence and determine behavior."

David Velleman at Left2Right blog argues here that the significance of this basic research on fruit flies is overstated when applied to humans.  As part of his analysis, he adds this nugget about human sexual orientation (footnote omitted):

To begin with, virtually all research on sexual orientation relies on something like the "Kinsey scale", which measures orientation on a seven-point scale (0 to 6).  The lay conception of homosexuality as an all-or-nothing trait has no basis in scientific observation.  And the best-designed studies of identical twins have found that in over two-thirds of the pairs that include a homosexual twin (scoring 1 or higher on the Kinsey scale), the other twin is not homosexual.  This finding decisively rules out the possibility that sexual orientation is genetically determined, though further statistical analysis shows that it is indeed significantly influenced by genetic inheritance.

Comments

[murky]

Yes, but is David Velleman making an interesting or even non-trivial point in that excerpt? I don't think so. You might as well say we'll never find a gene for being tall either, because if you're born in the starving Sudan you won't grow as tall as you would grow up well fed in Beverly Hills.