The Science of Desire by Dean Hamer & Peter Copeland

Author:Dean Hamer & Peter Copeland
Language: eng
Format: epub
Publisher: Simon & Schuster
Published: 1994-07-15T00:00:00+00:00

WHAT THE STUDY DID NOT SHOW

Proving that a gene exists is one thing. Isolating or finding the gene, measuring its incidence and effect on people, and understanding how it works is another, and those goals may take many years to achieve. Given the brief history of the genetic study of sexual orientation, we’re pleased to have made as much progress as we have, but many things, indeed most things, remain to be explored.

Population Parameters

Our study was not designed to address the role of the Xq28 locus in the population at large or even among all gay men. Mary-Claire King, discoverer of the breast-cancer locus, made this point most succinctly: “It is impossible to use either the family history or the linkage data to estimate the magnitude of genetic influence on homosexuality in the general population.”

King then outlined some of the questions that remain to be answered. What fraction of all gay men carry an Xq28-linked allele that influenced their sexual orientation? What is the frequency of this allele among heterosexual men? How many different alleles are present at Xq28, and what is the effect of each? What other genes and nongenetic factors influence sexual orientation, and what role does each play?

Our study could not address these questions because we deliberately studied a population enriched for the gene we were searching for—enriched because we only studied those families with two gay brothers, no gay fathers, and no more than one lesbian. This selected population was necessary to determine whether a gene on the X chromosome had any effect on sexual orientation, but it could not show the precise magnitude of that effect.

To estimate the role of Xq28 in the population at large, researchers would have to isolate the gene, determine what parts of the DNA sequence were variable, and then perform a population-based survey on a large number of individuals with various sexual identifications. The results of such an experiment on a particular population, say residents of Washington, D.C., still would be limited and would not necessarily apply to other populations, such as Salt Lake City or Tokyo, where the same genes might express themselves differently because of the different cultural environments. A person with a “gay gene” growing up in a repressive society, for example, might develop differently than someone with the same gene growing up in a permissive society.

This type of measurement is still a long way from being feasible. In the meantime, we can make only educated guesses about the importance of Xq28 in the population at large. On the high side, the region couldn’t possibly influence more than 67 percent of gay men, the proportion “linked” to this region in our highly selected group of gay siblings. On the low side, if much of homosexuality is caused by environmental factors, or by a large number of interacting genes, Xq28 could account for as little as a few percent of the variation in male sexual orientation. The median range, taken from our linkage data and from the available twin and family studies, suggests that Xq28 plays some role in about 5 to 30 percent of gay men.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.