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.Hamer s research team recruited an original group of 76 gay men for apedigree study.(A pedigree study is an attempt to determine how a traitis distributed among members of a kin group.) One or more relatives from26 of these men s families were also interviewed, for a total of 122 partici-pants.Hamer s team found elevated levels of homosexuality among gaymen s maternal uncles and among their maternal cousins, linked by aunts,as compared to their paternally linked relatives.Hypothesizing transmis-sion of a homosexual gene through the X chromosome, the researchers thenrecruited 38 pairs of gay brothers for a second pedigree study.These pairsof gay brothers were specifically culled from families without known les-bians or paternally linked homosexuals in order to eliminate subjects likelyto display nonmaternal routes of transmission. The second pedigreestudy found a somewhat more pronounced maternal pattern.Finally, theHamer team performed DNA linkage analysis on the 38 pairs of gay broth-ers from the second pedigree study, plus two pairs of gay brothers from thefirst study.Hamer et al.reported that 33 of 40 pairs (or 82 percent) shareda DNA marker, Xq28, located on the tip of the X chromosome.(The term DNA marker denotes a strip of DNA that is usually transmitted whole from parent to offspring; it thus allows geneticists to work with units of afew million base pairs of DNA, rather than trying to sort out individual genesfrom among several billion base pairs.Xq28, as the authors note, is large The Biology of the Homosexual / 249enough to contain several hundred genes.)25 Hamer et al.conclude: We havenow produced evidence that one form of male homosexuality is preferen-tially transmitted through the maternal side and is genetically linked to chro-mosomal region Xq28. The authors suggest that a thorough mapping ofthe region will eventually yield a gene involved in homosexual expression,but they also suggest that more than one gene might contribute to sexualorientation, and that environmental factors also play a role.26 ( Hey, Mom,Thanks for the Genes! is the message that with minor variations appearedon gay T-shirts across the country a line that proved even more popularthan the camp come-on How Big Is Your Hypothalamus? )In his scientific (as opposed to journalistic or popularizing) publications,Hamer has been careful to avoid extreme variants of biological determin-ist arguments.Indeed, Hamer himself often points out that a link is notthe same as a cause. He distinguishes between genetic influences and genetic destiny, and even while in search of a gay gene, he often putsthe term inside eyebrow-raising quotation marks.27 Still, there is some-thing less than fully congruous about searching for a gay gene whileclaiming that one does not exist, and the problems with Hamer s study arequite serious.The pedigree studies invite certain preliminary observations.First, not allof the families in Hamer s samples exhibit the maternal pattern high-lighted in the subsequent genetic study of gay brothers.The results suggesta significant but not dramatic elevation of homosexuality among the ma-ternally linked relatives of gay men.Next, some of the raw numbers supporting the idea of a maternal link-age are in fact quite low.In the first pedigree study, 7 of 96 gay men (7.3percent) reported having a gay maternal uncle, as opposed to only 2 of 119(1.7 percent) who reported a gay paternal uncle.But there is little differ-ence between the 4 of 52 (7.7 percent) who reported a gay maternal cousinon their aunt s side and the 3 of 56 (5.4 percent) who reported a gay pater-nal cousin on their uncle s side.In consequence, the difference between rates of homosexuality amongmaternal and paternal kin is statistically significant only if one assumes a(relatively low) 2 percent base rate of male homosexuality.As EdwardStein and others have pointed out, the difference becomes statistically in-significant if one assumes a (more plausible) base rate of 4 percent.28Finally, given such small raw numbers, Hamer s pedigree analysis is opento charges that it fails to account for even the most obvious relevant effects 250 / Permutations on the Nature of Desireof gender and family relations in American society.Women mothersplay a much greater role than men in negotiating and cementing family ties,a tendency that is well established in the sociological and anthropologicalliterature.29 As a result, Americans tend to be closer to and to know moreabout their maternal relatives than their paternal ones.This sociological ef-fect is likely to be even more pronounced in the case of gay men than in so-ciety at large.Given the role of fathers in perpetuating cultural expectationsof masculinity, given the cultural anxieties that a gay son reflects upon hisfather, and given the nature of the idealized maternal role (nurturing care-giver), it is certainly conceivable that on the average, gay men tend to becloser to their mothers and to know more about their maternal, consan-guineal kin than they are to their fathers, about whose blood relations theyknow correspondingly less.30Hamer s team did attempt to apply a reasonable check on informationprovided by the gay men.They also interviewed at least one relative eachfor twenty-six participants (for a total of forty-six relatives interviewed).Onthis basis, Hamer concluded that the information provided by the seventy-six total participants was reliable.One might suggest, instead, that the claimswere merely consistent: that one relative tended to think pretty much whatanother relative thought.Since extensive networks of the gay men s rela-tives were not systematically interviewed, either or both of the above soci-ological factors could fully account for the maternally skewed results ofHamer s pedigree study.31At this point in a review of Hamer s study, it is usually conceded: Yes, butHamer s group nonetheless found something a genetic marker sharedby gay brothers, and that is in itself significant. And after all, Hamer sgroup claims only to have established a genetic link for one form of malehomosexuality presumably the kind genetically transmitted along ma-ternal lines.Still, there is considerably less significance here than one couldglean from media reports, which took Hamer s study as the charmed thirdto seal the argument.It is important to specify first what has not been shown by Hamer s group.First, no gay gene has been identified.Nor can we safely conclude thatone is there, in Xq28, like a needle in the proverbial haystack, awaiting dis-covery.All kinds of traits run in families without having a genetic basis.And because human populations are quite variable, when a trait runs infamilies, a DNA sequence that is a marker for a particular trait in onefamily may not be associated with that trait in another [ Pobierz całość w formacie PDF ]
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.Hamer s research team recruited an original group of 76 gay men for apedigree study.(A pedigree study is an attempt to determine how a traitis distributed among members of a kin group.) One or more relatives from26 of these men s families were also interviewed, for a total of 122 partici-pants.Hamer s team found elevated levels of homosexuality among gaymen s maternal uncles and among their maternal cousins, linked by aunts,as compared to their paternally linked relatives.Hypothesizing transmis-sion of a homosexual gene through the X chromosome, the researchers thenrecruited 38 pairs of gay brothers for a second pedigree study.These pairsof gay brothers were specifically culled from families without known les-bians or paternally linked homosexuals in order to eliminate subjects likelyto display nonmaternal routes of transmission. The second pedigreestudy found a somewhat more pronounced maternal pattern.Finally, theHamer team performed DNA linkage analysis on the 38 pairs of gay broth-ers from the second pedigree study, plus two pairs of gay brothers from thefirst study.Hamer et al.reported that 33 of 40 pairs (or 82 percent) shareda DNA marker, Xq28, located on the tip of the X chromosome.(The term DNA marker denotes a strip of DNA that is usually transmitted whole from parent to offspring; it thus allows geneticists to work with units of afew million base pairs of DNA, rather than trying to sort out individual genesfrom among several billion base pairs.Xq28, as the authors note, is large The Biology of the Homosexual / 249enough to contain several hundred genes.)25 Hamer et al.conclude: We havenow produced evidence that one form of male homosexuality is preferen-tially transmitted through the maternal side and is genetically linked to chro-mosomal region Xq28. The authors suggest that a thorough mapping ofthe region will eventually yield a gene involved in homosexual expression,but they also suggest that more than one gene might contribute to sexualorientation, and that environmental factors also play a role.26 ( Hey, Mom,Thanks for the Genes! is the message that with minor variations appearedon gay T-shirts across the country a line that proved even more popularthan the camp come-on How Big Is Your Hypothalamus? )In his scientific (as opposed to journalistic or popularizing) publications,Hamer has been careful to avoid extreme variants of biological determin-ist arguments.Indeed, Hamer himself often points out that a link is notthe same as a cause. He distinguishes between genetic influences and genetic destiny, and even while in search of a gay gene, he often putsthe term inside eyebrow-raising quotation marks.27 Still, there is some-thing less than fully congruous about searching for a gay gene whileclaiming that one does not exist, and the problems with Hamer s study arequite serious.The pedigree studies invite certain preliminary observations.First, not allof the families in Hamer s samples exhibit the maternal pattern high-lighted in the subsequent genetic study of gay brothers.The results suggesta significant but not dramatic elevation of homosexuality among the ma-ternally linked relatives of gay men.Next, some of the raw numbers supporting the idea of a maternal link-age are in fact quite low.In the first pedigree study, 7 of 96 gay men (7.3percent) reported having a gay maternal uncle, as opposed to only 2 of 119(1.7 percent) who reported a gay paternal uncle.But there is little differ-ence between the 4 of 52 (7.7 percent) who reported a gay maternal cousinon their aunt s side and the 3 of 56 (5.4 percent) who reported a gay pater-nal cousin on their uncle s side.In consequence, the difference between rates of homosexuality amongmaternal and paternal kin is statistically significant only if one assumes a(relatively low) 2 percent base rate of male homosexuality.As EdwardStein and others have pointed out, the difference becomes statistically in-significant if one assumes a (more plausible) base rate of 4 percent.28Finally, given such small raw numbers, Hamer s pedigree analysis is opento charges that it fails to account for even the most obvious relevant effects 250 / Permutations on the Nature of Desireof gender and family relations in American society.Women mothersplay a much greater role than men in negotiating and cementing family ties,a tendency that is well established in the sociological and anthropologicalliterature.29 As a result, Americans tend to be closer to and to know moreabout their maternal relatives than their paternal ones.This sociological ef-fect is likely to be even more pronounced in the case of gay men than in so-ciety at large.Given the role of fathers in perpetuating cultural expectationsof masculinity, given the cultural anxieties that a gay son reflects upon hisfather, and given the nature of the idealized maternal role (nurturing care-giver), it is certainly conceivable that on the average, gay men tend to becloser to their mothers and to know more about their maternal, consan-guineal kin than they are to their fathers, about whose blood relations theyknow correspondingly less.30Hamer s team did attempt to apply a reasonable check on informationprovided by the gay men.They also interviewed at least one relative eachfor twenty-six participants (for a total of forty-six relatives interviewed).Onthis basis, Hamer concluded that the information provided by the seventy-six total participants was reliable.One might suggest, instead, that the claimswere merely consistent: that one relative tended to think pretty much whatanother relative thought.Since extensive networks of the gay men s rela-tives were not systematically interviewed, either or both of the above soci-ological factors could fully account for the maternally skewed results ofHamer s pedigree study.31At this point in a review of Hamer s study, it is usually conceded: Yes, butHamer s group nonetheless found something a genetic marker sharedby gay brothers, and that is in itself significant. And after all, Hamer sgroup claims only to have established a genetic link for one form of malehomosexuality presumably the kind genetically transmitted along ma-ternal lines.Still, there is considerably less significance here than one couldglean from media reports, which took Hamer s study as the charmed thirdto seal the argument.It is important to specify first what has not been shown by Hamer s group.First, no gay gene has been identified.Nor can we safely conclude thatone is there, in Xq28, like a needle in the proverbial haystack, awaiting dis-covery.All kinds of traits run in families without having a genetic basis.And because human populations are quite variable, when a trait runs infamilies, a DNA sequence that is a marker for a particular trait in onefamily may not be associated with that trait in another [ Pobierz całość w formacie PDF ]