This is the Psychology article I used.

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

Archives of Sexual Behavior, Vol. 32, No. 2, April 2003, pp. 103–114 ( C! 2003)

Handedness, Sexual Orientation, and Gender-Related Personality Traits in Men and Women

Richard A. Lippa, Ph.D.1

Received April 19, 2002; revision received October 1, 2002; accepted November 15, 2002

This study assessed large numbers of heterosexual and homosexual men and women on handedness andgender-relatedpersonality traits. Initialanalysesemployedadichotomousmeasureofhandedness (right-handed vs. non–right-handed). For men and women combined, homosexual participants had 50% greater odds of being non–right-handed than heterosexual participants, a statistically significant difference.Homosexualmenhad82%greateroddsofbeingnon–right-handedthanheterosexualmen, astatisticallysignificantdifference,whereashomosexualwomenhad22%greateroddsofbeingnon– right-handedthanheterosexualwomen,anonsignificantdifference.Whenparticipantswereclassified into five graduated categories of handedness, both men and women showed significant homosexual– heterosexualdifferences inhandednessdistributions.Withingroups,handedness showedanumberof weak but statistically significant associations with sex-typed occupational preferences, self-ascribed masculinity, and self-ascribed femininity, but not with instrumentality or expressiveness. Rates of non–right-handedness were virtually identical for heterosexual men and women, suggesting that sex differences in handedness may result from higher rates of homosexuality in men.

KEY WORDS: handedness; sexual orientation; sex differences; masculinity; femininity.

INTRODUCTION

Ina recentmeta-analysis,Lalumière,Blanchard,and Zucker(2000)compiledevidenceonassociationsbetween handedness and sexual orientation in men and women. Data from 6,182 homosexual and 14,808 heterosexual men showed that homosexual men had 34% greater odds of being non–right-handed than heterosexual men, and datafrom805homosexualand1,615heterosexualwomen showed that homosexual women had 91% greater odds of being non–right-handed than heterosexual women. Both of these differences were statistically significant. A num- ber of recent studies have also indicated that gender iden- titydisorder isassociatedwithnon–right-handedness (see Green and Young, 2001, and Zucker, Beaulieu, Bradley, Grimshaw, and Wilcox, 2001, for reviews and new data).

Although there is now considerable evidence for an association between non–right-handedness and certain kinds of strong gender-atypicality (e.g., homosexuality,

1Department of Psychology, California State University, Fullerton, California 92834; e-mail: [email protected].

gender identity disorder), the evidence is weaker for associations between handedness and other kinds of gender-related individual differences. Perhaps the best- documented finding is that there are slightly higher rates of left-handedness in males than females. In an interna- tional survey of over 11,000 participants, for example, Perelle and Ehrman (1994) reported that 10.6% of male participantsand8.5%offemaleparticipantsreportedwrit- ing with their left hands, and in a compilation of data from over 12,000 children, Zucker et al. (2001) reported that 11.8% of boys and 9.0% of girls were left-handed. Finally, a meta-analysis by Seddon and McManus (1991) compiled results from88studieswithmore thanaquarter of a million participants and found that 8.5% of men and 6.7% of women were left-handed, with men’s incidence of left-handedness 27% higher than women’s. Although a number of theories have attempted to explain the small but reliablesexdifferences typically foundinhandedness, these differences remain poorly understood.

A few studies have examined associations between handedness and gender-related personality traits within each sex. For example, Nicholls and Forbes (1996)

103 0004-0002/03/0400-0103/0 C! 2003 Plenum Publishing Corporation

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

104 Lippa

reported that 40 left-handed women scored higher on in- strumentality (i.e., dominance) and lower on expressive- ness (i.e.,nurturance) thandid40right-handedwomen. In a study of 340 college women, Casey and Nuttall (1990) reported a number of significant associations between “anomalousdominance”(beingnon–right-handedorhav- ing non–right-handed first-degree relatives) and instru- mentalityandexpressivenessasassessedbytheBemSex- Role Inventory and masculinity as assessed by a tomboy scale. In general, women with “anomalous dominance” showed more male-typical traits than purely right-handed women. Santhakumari, Kurian, and Rao (1994) reported that, among 124 Indian women, non–right-handedness was associated with higher levels of masculinity as as- sessed by Blanchard and Freund’s (1983) gender iden- tity scale.Finally,Coren (1994) reported that left-handers were higher than right-handers on interpersonal circum- plex scales that assessed how “arrogant/calculating” and “coldhearted”participantswere.Theseassociationswere found both for college men and women, suggesting that left-handed individuals, whether male or female, show more male-typical traits, that is, higher dominance and lowernurturance.Coren (1994) speculated that theremay be environmental causes for some personality differences between left and righthanders (e.g., social influences re- sulting from the minority status of being left-handed). In sum, several studies suggest that various indices of masculinity are associated with non–right-handedness in women. Evidence on links between gender-related traits and handedness in men is much more limited.

The study to be reported here extended previous re- search on handedness and gender-related traits in two ways. First, it assessed large samples of both homosexual and heterosexual men and women. This permitted both between-sex and within-sex analyses of handedness cor- relates. Second, this study assessed participants on sev- eral different kinds of gender-related personality traits, including male- versus female-typicality of occupational preferences,self-ascribedmasculinity,self-ascribedfemi- ninity, instrumentality, and expressiveness. These various measures of masculinity and femininity permitted a more componential analysis of which gender-related traits are and which are not associated with handedness.

Because large numbers of heterosexual and homo- sexual men and women were assessed, it was possible to examine associations between handedness and gender- relatedtraitswithinsexualorientationgroupsaswellasfor all men combined and for all women combined. Demon- strating within-group associations between handedness andgender-related traitswould indicate thatnotonlydoes handedness differ between gender-atypical and control

populations (e.g., between homosexual and heterosexual individuals)butalsothathandednesscovarieswithgender- related traits in largeandrepresentativepopulationsofho- mosexual and heterosexual men and women. In addition, the large sample sizes permitted analyses of finer grada- tions of handedness than have been studied previously.

The results reported here—both on associations be- tween handedness and sexual orientation and on associ- ations between handedness and gender-related individual differences within sexual orientation groups—may help to test among theories that have attempted to explain as- sociations between handedness and gender-related traits. Among the most prominent of these theories are prena- talhormone theory (e.g.,Geschwind&Galaburda,1985), pathological left-handedness theory (e.g., Previc, 1996; Satz, 1972), developmental instability theory (Yeo & Gangestad, 1998), and maternal immunoreactivity theory (Blanchard & Klassen, 1997). A brief summary of each of these theories follows.

Prenatal Hormone Theory

Prenatal hormone theory proposes that both hand- edness and sexual orientation are influenced by prenatal androgen levels, with higher androgen exposure hypoth- esized to produce more male-typical patterns of develop- ment, including a greater incidence of left-handedness. One problem with prenatal hormone theory is that male homosexuality (i.e., a female-typical pattern of sexual attraction) is associated with the more male-typical pattern of handedness—left-handedness. In regard to gender-relatedpersonality traits, themost straightforward prediction of prenatal hormone theory is that, within sex- ual orientation groups, non–right-handedness will be as- sociated with masculine traits both for men and women. Some theorists have speculated about possible nonlinear effects of androgens, and they have proposed that the ef- fectsofandrogensmaybecomplexbecausestress-induced androgens may abnormally surge at some stages of pre- natal developmentbut thendeclineat other times, leading to paradoxical effects (e.g., see James, 1989). The current predictionsarebasedonasimplelinearversionofprenatal hormone theory—that prenatal androgens “masculinize” behaviorwithineachsexandthatmales,onaverage, show masculinizedpatternsofbehaviorcomparedwithfemales. Left-handedness isassumed tobe the“masculinized”pat- tern of handedness, because males show higher rates of left-handedness than females.

A central piece of evidence motivating the prenatal hormone theory of handedness is the finding that non– right-handedness occurs more often in males than in fe- males. In their meta-analytic review of studies on

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

Handedness and Sexual Orientation 105

handedness and sexual orientation, however, Lalumière et al. (2000) cautioned:

It should be kept in mind that the small sex difference in handedness may be simply due to the fact that more men thanwomenarehomosexuals . . . and thatmoremen than women are affected by conditions associated with hand- edness, such as autism and dyslexia. . . . There might not be any sex difference in handedness among “unaffected” samples. (p. 586)

Because this study assessed large samples of men and women on sexual orientation as well as on handedness, it provided data that could be used to test Lalumière et al.’s hypothesis.

Pathological Left-Handedness Theory

Pathological left-handedness theory proposes that some cases of left-handedness are caused by patholog- ical stressors, such as birth traumas and brain injuries. Considerable evidence shows that left-handedness is, in fact, associated with a number of neurological and devel- opmental problems, including learning disabilities, intel- lectual retardation, autism, schizophrenia, cerebral palsy, epilepsy, deafness, and strabismus (Previc, 1996). To ap- ply pathological left-handedness theory to gender-related traits, one must further assume that gender-atypical traits andbehaviorsaresometimesalsocausedbystressorssuch as toxins,birth trauma,andbrain injuries (e.g., seeEllis& Cole-Harding,2001).CorenandSearleman’s (1990)Rare TraitMarkerModeladdsastatistical twist topathological left-handedness theory; see also Coren & Halpern, 1991). This model proposes that various kinds of developmental stressorsandtraumasmayswitchanindividual’s“natural” handedness.Since“natural” right-handers areassumed to be much more common than “natural” left-handers, de- velopmental stressors would therefore switch many more right-handers to non–right-handedness than vice versa. Thus,statisticalassociationsbetweenleft-handednessand variouskindsofdevelopmentalpathologymaynotbedue to the fact that left-handedness is intrinsically associated withpathologicalprocesses,butrathertothefactthat there are initially so many more “natural” right-handers than left-handers.

Developmental Instability Theory

Developmental instability theory argues that biolog- ical development is influenced by noise-like variations, which are likely to perturb the organism from optimal de- velopment (i.e., development leading to optimal fitness). Such variations may result from mutations, from genetic

variations insusceptibility inenvironmental stressors,and from environmental variations and stressors (such as in- fectious agents and toxins). Yeo and Gangestad (1998) have argued that moderate right-handedness is the opti- mal evolvedhuman trait and therefore thatdevelopmental instability leads both to non–right-handedness and to ex- tremeright-handedness.Developmental instability theory may be applied to gender-related traits if one makes the additional assumption that gender-atypical traits, such as homosexuality and gender identity disorder, may also re- sult from developmental instability.

According to Yeo and Gangestad’s (1998) theory, gender-atypical behaviors could be linked either to non– right-handedness or to extreme right-handedness. How- ever,giventhemodalmoderateright-handednessproposed by Yeo and Gangestad and applying reasoning similar to that of the Rare Trait Marker Model, one could argue that shifts to non–right-handedness would be more apparent and frequent in human populations than shifts to extreme right-handedness.Developmental instability theory there- fore suggests that non–right-handedness will be linked to gender-atypical traits in both men and women. It is worthnoting thatYeoandGangestad’sempirical research employed behavioral rather than self-report measures of handedness, and extreme right-handedness may be hard to detect with the kinds of self-report measures typically used in large-scale studies of handedness.

Maternal Immunological Theory

Finally, maternal immunological theory proposes that maternal antibodies to Y-linked minor histocompati- bility antigens may affect the neural development of male but not female fetuses. This theory was developed to ex- plain the empirical finding that older male siblings in- crease the odds that males but not females will be ho- mosexual (Blanchard,1997;Cantor,Blanchard,Paterson, & Bogaert, 2002). To account for links between hand- edness and gender-related traits, maternal immunological theory would need to assume further that maternal im- munological reactions influence handedness as well as gender-atypical traits. Two kinds of evidence would be consistent with this theory: (1) if males, but not females, showanassociationbetweenhandednessandtheirnumber ofolderbrothers, and (2) if linksbetweenhandednessand gender-related traitsarestronger formen thanforwomen.

In regard to the second prediction, Lalumière et al.’s (2000) meta-analysis found that the relationship between handednessandsexualorientationwasstrongerforwomen than for men, and this seems to argue against maternal immunological processes as mediators of the association between handedness and sexual orientation. It is worth

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

106 Lippa

noting, however, that Lalumière et al. compiled handed- ness data from many more homosexual men (over 6,000) thanhomosexualwomen(805),andtherefore theiroverall estimateofnon–right-handed-ness inhomosexualwomen may be less reliable than their estimate for men.

Lalumièreetal. (2000)speculatedthat therecouldbe commongenes that influencebothhandednessandmater- nal immunological mechanisms to male tissue:

. . . perhaps there is some overlap between those MHC [major histocompatibility complex] alleles that correlate withnon-right-handednessandthosethatrenderHYanti- gens lessvisible toneighboringneurons in thefetalbrain, thus diminishing a signal that contributes to the sexual differentiation of the brain in the male-typical pattern. (p. 587)

Onceagain,thishypothesiswouldseemtopredicthanded- ness and sex-typing associations in males but not females.

Bryden, McManus, and Bulman-Fleming (1994) conducted a meta-analysis that showed that left-handed- ness isassociatedwithvariousautoimmunedisorders,and Yeo and Gangestad (1998) reported evidence that certain alleles associated with autoimmune disorders are more commoninleft-handers(seeGangestadetal.,1996).Such findingshint that the immunesystemsof left-handersmay be disregulated in broader ways than those suggested by maternal immunological theory. If such broader immune processes are linked to the development of gender-related traits and handedness, they too might provide a possi- ble explanation for associations between handedness and gender-related traits.

In summary, prenatal hormone theory—at least, in its most straightforward (i.e., linear) version—predicts thatnon–right-handedness(themoremale-typicalpattern) will be associated with homosexuality in women but with heterosexuality in men. It also predicts that non–right- handedness will be associated with masculinity in both women and men. Pathological left-handedness theory— with the added assumption that environmental traumas and stressors may lead both to left-handedness and to homosexuality—predicts an association between homo- sexuality and non–right-handedness in both men and women. Pathological left-handedness theory does not make a clear prediction about associations between hand- edness and measures of masculinity and femininity in “normal,” nonpathological populations of men and women. In contrast, developmental instability theory seemscompatiblewith thenotion thathandednessmaybe associated with normal within-group variations in mas- culinity and femininity as well as with sexual orienta- tion.Thisisbecausevariationsinhandedness,masculinity and femininity, and sexual orientation may all be due, to

some extent, to perturbations in development. Develop- mental instability theory may overlap with pathological left-handedness theory, insofar as extreme kinds of devel- opmental instability may result in pathological outcomes. Finally, maternal immunological theory, to the extent that it applies tohandednessaswell as togender-related traits, implies thatassociationsbetweenhandednessandgender- related traits shouldbestronger formales thanfor females and that handedness will be associated with number of older brothers for men but not for women. This study provides data relevant to these hypotheses by assessing handedness, sexual orientation, gender-related personal- ity traits,andnumbersofolderbrothersandsisters in large samplesofhomosexualandheterosexualmenandwomen.

METHOD

Participants

Most homosexual participants were volunteers so- licited at gay pride festivals in Long Beach and Orange County, California. The remainder were college students and university staff. Homosexual participants were 461 men, with a mean age of 37 (SD = 11.18, range = 17–76), and 472 women, with a mean age of 36 (SD = 9.98, range = 17–69). Heterosexual participants were 351menand707women,mostofwhomwerestudentsand staff at California State University, Fullerton. The mean age of heterosexual men was 24 (SD = 10.69, range = 12–85; apart from one 12-year-old, all participants were 17 or older), and the mean age of heterosexual women was 23 (SD = 8.89, range = 15–83).2 Although the ho- mosexual samples were, on average, significantly older than the heterosexual samples, none of the results that followweremuchalteredwhenoldergayand lesbianpar- ticipants (those over 30) were excluded from analyses, and so the full sample was included to maximize statisti- cal power.3 Also, in some analyses, age was treated as a covariate without changing results.

2The 12-year-old boy who participated in the study was attending a gay pride festival with his mother, and he participated in the study with the consent of his mother. All participants were informed that they could leave questionnaire items blank if they felt uncomfortable answering any questions. 3One reviewer of this paper noted that because of their mean age dif- ferences, heterosexual and homosexual participants did not constitute comparable comparison groups. However, given that previous research shows that non–right-handedness tends to decrease with age (Coren & Halpern, 1991), the fact that homosexual participants were, on aver- age, older than heterosexual participants in this study would, if any- thing,decrease thechancesofdemonstratingan increased frequencyof non–right-handedness among homosexual participants. Furthermore,

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

Handedness and Sexual Orientation 107

Measures

Sexual Orientation

Participants were asked to check “true” or “false” to whether they used each of the following labels to de- scribe themselves: “heterosexual (straight),” “gay,” “lesbian,” and “bisexual.” Men and women were classi- fied, respectively, as “gay” or “lesbian” (i.e., homosex- ual) if they checked “true” to using these labels to de- scribe themselves. Men and women were classified as “heterosexual” if they checked “true” to using this la- bel to describe themselves and they checked false to us- ing the label “gay” (for men) or “lesbian” (women) to describe themselves, or if they did not respond to these items.

Handedness

Handednesswasassessedvia three self-report items. The first item “Are you left- or right-handed?” asked par- ticipantstorespondbycirclinganumberona5-pointscale thatrangedfrom1(completelyleft-handed) through3(use both hands equally) to 5 (completely right-handed). Two additional items asked “Which hand do you usually write with?” and “Which hand do you normally use to throw a ball?” Participants responded to each of these items by circling one of five responses: exclusively use left; mostly use left,equallyuseboth;mostlyuseright; andexclusively use right.

Continuous and categorical handedness measures were computed from self-report handedness items. The continuous measure was simply the mean of the three handedness items (! = .90, mean = 4.44, SD = 1.03, range = 1–5). The categorical measure was based on re- sponses to the first item, “Are you left- or right-handed?” Participants who responded 1, 2, or 3 in response to this item (completely left-handed to use both hands equally) wereclassifiedasnon–right-handed,whereasparticipants who responded 4 or 5 (responses on the right-handed side of the 5-point scale) were classified as right-handed. Us- ing this system, 14.5% of participants were classified as non–right-handed and 85.5% as right-handed.

theincidenceof left-handednessinthisstudy(i.e.,participantsrespond- ing 1 or 2 to the overall handedness item; see Table II) was 6.8% for heterosexual men and 8.1% for heterosexual women, which is well within the range of rates observed for men and women in previous studies. Thus, the incidence of left-handedness in heterosexuals seems unexceptional in this study, and thedata fromheterosexualparticipants would therefore seem to provide reasonable comparisons to the data from homosexual participants.

Number of Older Brothers and Sisters

Participantsrespondedtotwoquestions thatassessed their number of older brothers and sisters: “How many of the babies that your biological mother carried before you were boys (girls)?” Participants responded by circling a number that ranged from none to 10, or by circling a final response of more than 10.

Gender-Related Personality Traits

Participants completed the Bem Sex-Role Inventory (BSRI), a measure of instrumental and expressive traits (Bem, 1981), and a section that asked participants to rate their degree of preference for 40 occupations on a 5-point scalethatrangedfromstronglydislike tostronglylike.Par- ticipants also completed a 6-item scale by Storms (1979), which assessed their self-ascribed masculinity and femi- ninity (Items: “Howmasculine (feminine) isyourperson- ality?” “How masculine (feminine) do you act, appear, and come across to others?” “In general, how masculine (feminine) do you feel you are?”).

Occupational preference ratings were used to com- pute gender diagnosticity (GD) scores, which assessed the male- versus female-typicality of participants’ occu- pationalpreferences.Genderdiagnosticprobabilitieswere computed by applying multiple discriminant analyses to eight nonoverlapping subsets of participants’ 40 occupa- tional preference ratings (see Lippa, 1995, 2001, 2002a; Lippa & Connelly, 1990). Because of the large number of gay and lesbian participants, the heterosexual sample was multiplied by a factor of 10 when computing gender di- agnostic probabilities. The reason for this procedure was to guarantee that gay and lesbian participants constituted a minority of the sample used to compute GD scores (see Lippa, 2000, 2002b, and Lippa and Tan, 2001, for similar procedures).4

GD measures give the probability that an individ- ual is predicted to be male or female an the basis of his or her pattern of occupational preference ratings. High scores(closer to1.0)aremoremale-typicalandlowscores (closer to 0.0) are more female-typical. The reliabilities

4The reader may wonder, as did one reviewer, why a factor of 10 was chosen.Thegoalherewas tomakehomosexualparticipantsa relatively small minority and heterosexual participants a relatively large major- ity when computing GD scores. Experimentation with various factors of multiplication (5, 10, 15) shows that GD scores computed in the variously augmented samples correlate very strongly with one another, regardlessofthefactorofmultiplication.ThecomputationofGDscores therefore is a robustprocess thatyields reliableandvalid scoresas long as thenumberofheterosexualparticipants inasample isat least several times the number of homosexual participants.

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

108 Lippa

of GD probabilities for all participants, men, and women were .80, .76, and .79, respectively. Previous research has shown that GD scores correlate strongly (.95 and above) with a sex-typed occupational preference index computed by simply adding all items that males prefer significantly more than females and subtracting all items that females prefer significantly more than males (Lippa, 2002b).

BSRI short-form instrumentality and expressiveness were computed in standard ways (with scale items av- eraged rather than summed), and their reliabilities were .85 and .87, respectively. The three items assessing self- ascribed masculinity were averaged from Storms’ scale (Storm, 1979), as were the three items assessing self- ascribedfemininity.Thereliabilitiesof self-ascribedmas- culinity were .80 for men and .87 for women, and the reliabilities of self-ascribed femininity were .85 for men and .90 for women.

RESULTS

Handedness and Sexual Orientation

Categorical Handedness

Table I presents 2 (sexual orientation) " 2 (hand- edness) contingency tables for men, for women, and for bothsexescombined.Therewasasignificantdifferencein handedness frequencies for heterosexual and homosexual men ("2[1, N = 808] = 8.58, p = .003), with 11.4% of heterosexual men and 19.0% of homosexual men classi- fied as non–right-handed. Lalumière et al. (2000) recom- mended computing the odds ratio, which in this case was homosexual participants’ increased odds of being non– right-handed compared with heterosexual participants. This statistic is independent of sample base rates of hand- edness. For men, the computed odds ratio was 1.82, in- dicating that being homosexual increased a man’s odds of being non–right-handed by 82%. The 95% confidence interval for this odds ratio, using the formula provided by Haddock, Rindskopf, and Shadish (1998, p. 342), was (1.21, 2.72).

The corresponding contingency table for women yieldedanonsignificantdifferenceinhandednessfrequen- cies forheterosexual andhomosexualwomen("2[1, N = 1174] = 1.29, p = .255), with 12.0% of heterosexual women and 14.3% of homosexual women classified as non–right-handed. The odds ratio for women was 1.22, with a 95% confidence interval of (.87, 1.72), indicating thatbeinghomosexual increasedawoman’soddsofbeing non–right-handed by 22%.

Table I. Cross-Tabulation of Sexual Orientation by Two-Category Handedness for Males, Females, and Both Sexes Combined

Handedness

Sexual orientation Non–right-handed Right-handed

Males Heterosexual (N = 350) 40 (11.4%) 310 (88.6%) Homosexual (N = 458) 87 (19.0%) 371 (81.0%)

Females Heterosexual (N = 706) 85 (12.0%) 621 (88.0%) Homosexual (N = 468) 67 (14.3%) 401 (85.7%)

Combined Heterosexual (N = 1, 056) 125 (11.8%) 931 (88.2%) Homosexual (N = 939) 157 (16.7%) 782 (83.3%)

Note. There are 13 more participants in the table for males and females combined than in the summed totals from the tables for males only and femalesonly.This resulted fromasmall numberofparticipantswhodid not report their sex, but who did report their sexual orientation. When these participants were excluded from the table for males and females combined, the results were virtually unchanged.

Finally, the contingency table for men and women combined yielded a significant difference in handedness frequencies forheterosexual andhomosexualparticipants ("2[1, N = 1995] = 9.76, p = .002), with 11.8% of het- erosexuals and 16.7% of homosexuals classified as non– right-handed. The odds ratio for men and women com- bined was 1.50, with a 95% confidence interval of (1.16, 1.93), indicating that being homosexual increased an in- dividual’s odds of being non–right-handed by 50%.

Five-Category Handedness

Table II presents 2 (sexual orientation) " 5 (5- category handedness) contingency tables for men and for women.Thefivehandednesscategorieswerebasedonthe fivescalepoints thatparticipantsused in rating theirover- allhandedness.Therewasasignificantdifferenceinhand- edness frequencies across the five handedness categories forheterosexualandhomosexualmen("2[4, N = 808] = 13.21, p = .01). Similarly, for women, and in contrast to the2 " 2contingencytablepresentedinTableI, therewas a significant difference in handedness frequencies across the five handedness categories for heterosexual and ho- mosexualwomen("2[4, N = 1174] = 11.95, p = .018). The results for both men and women indicated that for homosexual participants, handedness was shifted away from complete right-handedness. However, homosexual men and women seemed to show somewhat different pat- terns of a leftward shift.

Included in Table II are odds ratios (homosexual to heterosexual) computed for each category of handedness

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

Handedness and Sexual Orientation 109

Table II. Cross-Tabulation of Sexual Orientation by Five-Category Handedness for Males and Females

Five-category handedness

Sexual orientation 1 (Completely left-handed) 2 3 (Use both hands equally) 4 5 (Completely right-handed)

Males Heterosexual (N = 350) 12 (3.4%) 12 (3.4%) 16 (4.6%) 109 (31.1%) 201 (57.4%) Homosexual (N = 458) 36 (7.9%) 27 (5.9%) 24 (5.2%) 109 (23.7%) 262 (57.2%) Odds ratio (homosexual 2.40 1.76 1.15 0.69 0.99 to heterosexual) for each handedness category vs. all other categories

Females Heterosexual (N = 706) 26 (3.7%) 31 (4.4%) 28 (4.0%) 164 (23.2%) 457 (64.7%) Homosexual (N = 468) 25 (5.3%) 22 (4.7%) 20 (4.3%) 143 (30.6%) 258 (55.1%) Odds ratio (homosexual 1.48 1.07 1.08 1.45 0.67 to heterosexual) for each handedness category vs. all other categories

versus all the other categories combined. Interestingly, both the data for men and for women show anomalous odds ratios for the moderate right-handedness category. However, the direction of effect was opposite for men and women. For men, moderately right-handed individ- uals showed the lowest odds of being homosexual (odds ratio = .69),whereas forwomen,moderately right- handed individuals showed elevated odds of being homosexual (odds ratio = 1.45), which were virtually indistinguishable from the similarly elevated odds of completely left-handed women (odds ratio = 1.48). Par- ticularly for men, the moderately right-handed group seemed to mark an inflection point in odds ratios—i.e., odds ratios steadily decreased from the completely left- handed to the moderately right-handed groups, but then rebounded somewhat for the completely right-handed group.

Continuous Handedness

A2(sex) " 2(sexualorientation)ANOVAoncontin- uoushandedness formenandwomencombinedyieldeda significant main effect for sexual orientation (F[1, 1987] = 9.80, p = .002), and a marginally significant interac- tion between sex and sexual orientation (F[1, 1987] = 2.43, p = .119), which reflected larger heterosexual– homosexual handedness differences for men (means of 4.54 vs. 4.31) than for women (4.50 vs. 4.42). When age was entered into this analysis as a covariate, the results werevirtuallyunchanged.Therewasasignificantmainef- fect forsexualorientation(F[1,1939] = 7.61, p = .006), and a marginally significant interaction between sex and sexual orientation (F[1, 1939] = 2.53, p = .112).

Handedness and Gender-Related Traits in Men and Women

Tables III and IV present correlations between con- tinuoushandednessandvariousgender-related traits (GD, self-ascribedmasculinity, self-ascribedfemininity, instru- mentality, and expressiveness). These correlations were computed separately for all men, heterosexual men, and homosexual men (Table III) and for all women, het- erosexual women, and homosexual women (Table IV). Because continuous handedness was a decidedly skewed measure, nonparamentric correlations (Spearman’s rho) are presented as well as Pearson product–moment correlations.

Tables III and IV show that the gender-related traits ofGD(male-vs. female-typicalityofoccupationalprefer- ences), self-ascribed masculinity, and self-ascribed fem- ininity sometimes showed significant associations with handedness, but instrumentality and expressiveness did not. For all men, non–right-handedness was associated with female-typical occupational preferences, self- ascribednonmasculinity,andself-ascribedfemininity.For all women, non–right-handedness was associated with male-typicaloccupationalpreferences, self-ascribedmas- culinity, and self-ascribed nonfemininity. GD was associ- atedwithhandedness forheterosexualwomen,butnot for homosexual women, with non–right-handedness weakly associated with more male-typical occupational prefer- ences. GD and self-ascribed masculinity were associated with right-handedness in gay men, and self-ascribed fem- ininity was associated with non–right-handedness in het- erosexual men.

The data in Tables III and IV suggest that, to the de- gree that correlations were significant, right-handed men

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

110 Lippa

Table III. Correlations Between Continuous Handedness and Gender-Related Personality Traits for All Males, Heterosexual Males, and Homosexual Males

All males Heterosexual males Homosexual males (N = 818–842) (N = 345–350) (N = 444–461)

Gender-related traits Pearson Spearman Pearson Spearman Pearson Spearman

GD .12### .07# .06 .06 .11# .07 Self Masc .12## .10## .08 .08 .11# .08† Self Fem $.08# $.10## $.11# $.15## $.05 $.06 BSRI I .02 $.01 $.03 $.03 .03 $.02 BSRI E $.05 $.04 $.06 $.04 $.02 $.03

Note. Higher handedness scores indicate greater right-handedness. Higher GD scores indicate more male- typicaloccupationalpreferences.SelfMasc = Self-AscribedMasculinity.SelfFem = Self-AscribedFem- ininity. BSRI I = Bem Sex-Role Inventory Instrumentality. BSRI E = Bem Sex-Role Inventory Expres- siveness. Pearson = Pearson product–moment correlation. Spearman = Spearman’s rho. † p < .10, two-tailed. # p < .05, two-tailed. ## p < .01, two-tailed. ### p < .001, two-tailed.

tended to be more masculine and less feminine than left- handed men, whereas right-handed women tended to be more feminine and less masculine than left-handed women. Partial correlations that controlled for age were also computed between handedness and gender-related traits, and these partial correlations were quite similar to the raw correlations presented in Table II.

Handedness and Number of Older Brothers and Sisters

The variables “number of older brothers” and “num- ber of older sisters” generally took the values 0, 1, and 2. However, there were a small number of outlier values for participantswithvery largenumbersofolderbrothersand sisters. To reduce the impact of these outlier values, vari- ableswere transformedtoreflect just threecategories:“no olderbrother (orsister),”“oneolderbrother (orsister),”or

Table IV. Correlations Between Continuous Handedness and Gender-Related Personality Traits for All Females, Heterosexual Females, and Homosexual Females

All females Heterosexual females Homosexual females (N = 1212–1227) (N = 697–707) (N = 464–470)

Gender-related traits Pearson Spearman Pearson Spearman Pearson Spearman

GD $.06# $.12### $.11## $.15### .03 $.05 Self Masc $.03 $.06# $.01 $.05 $.02 $.01 Self Fem .03 .07# .04 .06 $.01 $.01 BSRI I .03 .02 .05 .01 .00 .03 BSRI E .00 .01 .02 .01 $.02 $.02

Note. Higher handedness scores indicate greater right-handedness. Higher GD scores indicate more male- typicaloccupationalpreferences.SelfMasc = Self-AscribedMasculinity.SelfFem = Self-AscribedFem- ininity. BSRI I = Bem Sex-Role Inventory Instrumentality. BSRI E = Bem Sex-Role Inventory Expres- siveness. Pearson = Pearson product–moment correlation. Spearman = Spearman’s rho. # p < .05, two-tailed. ## p < .01, two-tailed. ### p < .001, two-tailed.

“two or more older brothers (or sisters).” The percent of participants in each of the three categories of number of olderbrotherswas55,27,and18%,respectively.Theper- centage of participants in each of the three categories of numberofolder sisterswas57,27, and16%, respectively.

One-way ANOVAs examined whether continuous handedness scores differed across the three “older broth- ers” or “older sisters” groups. These analyses were con- ducted for all men, heterosexual men, homosexual men and similarly, for all women, heterosexual women, and homosexualwomen.Noneof theseANOVAsshowedsig- nificant effects for number of older brothers or sisters.

Contingency tables, created separately for men and women, examined the frequency of right- and non–right- handed individuals in each of the three “number of older brother” (or “number of older sister”) groups. The only categorical handedness analysis that showed a significant relationship was that for handedness and number of older

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

Handedness and Sexual Orientation 111

sisters in men ("2[2, N = 801] = 6.44, p = .04). This significant effect reflected the fact that, for men, the per- centage of non–right-handed individuals increased with number of older sisters (the percent of non–right-handed menwithno,one,ormore thanoneolder sisterswas14.1, 17.6, and 23.3%, respectively).

SexDifferencesinHandednessAmongHeterosexuals

Sex differences in handedness were examined first for just heterosexual participants. A t test contrasting het- erosexual men’s and women’s continuous handedness scores showed no sex difference (t[1056] < 1, ns; male mean = 4.54 and female mean = 4.50). Similarly, a 2 (sex) " 2 (categorical handedness) contingency table for heterosexual participants showed no evidence for a rela- tionship between participant sex and handedness ("2[1, N = 1056] < 1, ns), with the percentage of non–right- handed males and females 11.4 and 12.0%, respectively.

In contrast, homosexual participants showed a ten- dencytosexdifferencesinhandedness.A t testcontrasting homosexual men’s and women’s continuous handedness scores yielded a marginally significant result (t[931] = $1.53, one-tailed p = .064; male mean = 4.31 and fe- male mean = 4.42). Similarly, a 2 (sex) " 2 (categori- calhandedness)contingencytableforhomosexualpartici- pants showed a marginally significant relationship between participant sex and handedness ("2[1, N = 926] = 3.66, p = .056),withthepercentageofnon–right- handed homosexual males (19.0%) greater than the per- centage of non–right-handed homosexual females (14.3%). Unlike heterosexual participants, homosexual participants tended to show the commonly reported sex difference,withmendisplayinghigher ratesofnon–right- handedness than women.

DISCUSSION

The current results replicated previous findings of an association between handedness and sexual orienta- tion, with homosexual participants showing higher rates of non–right-handedness than heterosexual participants. Incontrast to the resultsofLalumièreet al.’s (2000)meta- analysis, however, this study found that sexual orienta- tion differences in handedness tended to be larger for men than for women. If the current results for men were added to Lalumière et al.’s (2000) meta-analysis, they would alter its conclusions for men only modestly, given that the sample studied here (N = 460) was consider- ably smaller than their meta-analyzed sample of homo- sexual men (N = 6,182). However, the current results for women would likely have a more dramatic impact,

for the current sample of homosexual women (N = 461) was quite large in comparison to the combined sample of homosexual women reviewed by Lalumière et al. (N = 805).

Complicating the current results, however, was the finding that gradations of handedness made a difference in observed links between handedness and sexual orien- tation. Although this study did not find a significant dif- ference between heterosexual and homosexual women’s handedness when using a dichotomous handedness clas- sification, it did find significant differences when using a 5-category classification of handedness. In a recent study of 205 homosexual men and 149 homosexual women, Mustanski, Bailey, and Kaspar (2002) found larger as- sociations between handedness and sexual orientation in women than in men, as did the Lalumière et al. meta- analysis; however, theseassociations resultedparticularly from sexual orientation differences in the number of am- bidextrous women. Additional studies will likely be needed to determine how the association between hand- edness andsexualorientationdiffers formenandwomen.

It is worth noting that this study employed a short 3-item measure of continuous handedness and a 1-item measure of dichotomous handedness. In their examina- tion of possible moderators of the relationship between handednessandsexualorientation,Lalumièreetal. (2000, p.584) reported that thenumberofhandedness itemsused inagivenstudydidnotmoderate therelationshipbetween handedness and sexual orientation. However, the specific handednessmeasureusedinastudydidshowamoderating effect, with the link between handedness and sexual ori- entationstronger instudiesusing theEdinburghInventory than in studies using the Annett questionnaire for partic- ipants’ writing hand. The Edinburgh Inventory, like the measure of handedness used in this study, includes items that ask which hand is used for writing and throwing. However, theEdinburghInventory includesother itemsas well, and its items are rated and scored differently than those in this study.Given itsgreater length, theEdinburgh Inventorymayhavegreater reliability than the1-itemand 3-item measures used here. If this is so, then the current results may have somewhat underestimated the relation between handedness and sexual orientation.

This study demonstrated a number of significant, albeitweak,associationsbetweenhandednessandgender- relatedpersonality traitswithin sexualorientationgroups. Specifically,non–right-handednessinmenwassometimes associated with more female-typical occupational preferences, self-ascribed femininity, and self-ascribed nonmasculinity. However, men’s handedness was not associated with their levels of instrumentality or expres- siveness. Among women, there was a tendency for

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

112 Lippa

non–right-handedness sometimes to be associated with moremale-typicaloccupationalpreferences,self-ascribed nonfemininity, and self-ascribed masculinity. As was the case for men, women’s handedness was not associated with their levels of instrumentality or expressiveness.

The current results provided little support for the simple version of prenatal hormone theory (for more di- rect evidence against the theory, see Grimshaw, Bryden, & Finegan, 1995). Consistent with previous studies, the current research found thatnon–right-handednesswasas- sociated with homosexuality (contrary to prenatal hor- monetheory’spredictionformen)andalsothatnon–right- handednesswasslightlyassociatedwithfemininityinmen and masculinity in women (again, contrary to prediction for men).

Furthermore, the current results call into question oneof thecentralunderlyingassumptionsofprenatalhor- mone theory—that sex differences in handedness result from sex differences in exposure to prenatal androgens. This assumption motivated the hypothesis that associa- tionsbetweenhandednessandsexualorientationmayalso be due to hormonal mediators. The current data showed no sex differences in handedness among heterosexuals, despite certain and large sex differences in their prena- tal exposure to androgens. Thus, the reasoning of prena- tal hormone theory may be backward. Rather than sex differences in handedness suggesting a simple hormonal explanationforassociationsbetweenhandednessandsex- ual orientation, the greater non–right-handedness of ho- mosexual individuals and the greater prevalence of male homosexuality may help explain sex differences in hand- edness. However, this explanation for sex differences in handednessleavestheassociationbetweenhomosexuality and non–right-handedness unexplained.

Likeprenatalhormone theory,maternal immunolog- ical theory was not consistently supported in this study. There was no evidence that men’s handedness was asso- ciated with their number of older brothers. However, con- sistent with maternal immunological theory, the current data showeda tendency for associationsbetweenhanded- ness and gender-related traits to be stronger for men than women. As noted before, the current finding that hand- edness and sexual orientation was more strongly linked in men than women was at odds with the findings of Lalumière et al.’s (2000) meta-analysis, and the issue of sex differences in links between handedness and sexual orientation is best regarded as unresolved.

In choosing between the two remaining theories— pathological left-handedness theory and developmental instability theory—the current findings nod slightly in the direction of the latter theory. One intriguing finding that seems consistent with Yeo and Gangestad’s (1998)

developmental instability theory is the finding that, for both men and women, moderately right-handed partici- pants showed anomalous results, with moderately right- handed men showing the lowest odds of homosexual- ity and moderately right-handed women showing high odds. The findings for men seem the most consistent with YeoandGangestad’s (1998) theory—thatmoderate right- handednessmaybeassociatedwith the leastdevelopmen- tal instability. The findings for women are more puzzling. At the very least, they suggest that associations between handedness and sexual orientation and their mediating processes may differ for men and women. Given that gra- dations of handedness seem to be significant, the current findings lead to thefollowingrecommendation:Future re- searchers should use more finely graduated measures of handedness when possible, and they should assess suffi- ciently large numbers of participants so that analyses on graduated handedness categories yield statistically reli- able results.

Although the current findings lend some support to developmental instability theory over pathological left- handedness theory, it is important to note that these two theories may not be independent. This study found some associationsbetweenhandednessandgender-relatedtraits in large, representative populations of men and women as well as associations between handedness and sexual orientation. As noted before, developmental instability theory seems compatible with the notion that sexual ori- entation, other gender-related traits, and handedness may all be influenced by perturbations in development. Patho- logical left-handedness theory, however, does not make strong predictions about associations between handed- ness and individual differences in gender-related person- ality traits in “normal” populations. Of course, it may be the case that “normal” populations include individu- als with various kinds and various degrees of pathology, and it may also be the case that developmental stressors and their developmental sequelae represent a continuum rather thanan“either–or” (pathological vs. nonpathologi- cal)phenomenon.The“continuous”viewofstressorsand their developmental outcomes is consistent with develop- mental instability theory.

The finding that handedness and gender-related per- sonality traits showed associations for men as well as for women is significant, given that most previous re- search has focused on women. The current results lead to the recommendation that future research study men as well as women. This study found some evidence that the association between handedness and sexual orienta- tionwasstronger formen than forwomen. If this reported sex difference is replicated, how might it be explained by each of the four theories discussed earlier? Maternal

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

Handedness and Sexual Orientation 113

immunological theory directly predicts that certain asso- ciations (e.g., betweennumberofoldermalebrothers and sexual orientation) will be stronger for men than women, and thus it hints that other correlates of gender-related traits may also show sex differences.

To account for sex differences in the strength of as- sociations between handedness and gender-related traits, prenatal hormone theory might assume that there is more variabilityinexposuretoprenatalandrogensamongmales than females. This hypothesis is consistent with the as- sumptionthat femaledevelopment is thehuman“default,” whereasmaledevelopment requireshormonallymediated departures from the female “default” (Collaer & Hines, 1995). The multistage hormonal processes that lead to male rather than female development could be hypothe- sizedtoresult inmorevariableoutcomesformalesthanfor females. Pathological left-handedness theory might try to account for sex differences by proposing that male births, perhaps for both genetic and environmental reasons, are more stressed than female births. Finally, developmental instability theorymightpropose that, in regard tohanded- ness and gender-related traits, there is more developmen- tal instability in male than in female development. These various theoretical approaches are not necessarily inde- pendent. For example, variations is hormonally mediated processes may result from developmental instability and environmental stressors, and some kinds of pathological outcomes may be linked to developmental instability.

All of the hypotheses just proposed suggest ques- tions that are amenable to further empirical investigation. For example, are putative markers of prenatal androgen exposure more variable in males or in females, and are such markers linked to handedness? Are male births in factmorestressed thanfemalebirths, anddocertainkinds of birth stress affect both handedness and sexual orien- tation? Do males show more or less evidence of devel- opmental instability (e.g., fluctuating asymmetry, minor physical anomalies) than femalesdo?Given thatdevelop- mental instability theory (e.g., Yeo & Gangestad, 1998) hasproposed thatmoderate right-handedness is theevolu- tionarily optimal human trait and given that research gen- erated by developmental instability theory has assessed handednesswithperformancerather thanself-reportmea- sures, it would be of interest to examine whether sexual orientation and other gender-related traits are related to performanceaswell as to self-reportmeasuresofhanded- ness. Such research could study whether gender-atypical traitsareassociatedwithextremeright-handednessaswell as with non–right-handedness.

It is worth noting that in this study not all gender- related personality traits were equally associated with handedness. GD measures (i.e., male- vs. female-typical

occupational preferences), self-ascribed masculinity, and self-ascribed femininity showed some significant associ- ations with handedness, but instrumentality and expres- sivenessdidnot.Thesefindingsareconsistentwith recent research showing that GD, self-ascribed masculinity, and self-ascribed femininity show much stronger links to sex- ualorientation thandoinstrumentalityandexpressiveness (Lippa, 2000, 2002b).

At the same time, the current findings seem to con- tradict some previous studies on handedness and gender- related traits in women. As described earlier, a number of studies have found that non–right-handedness is asso- ciated with various kinds of masculinity in women, in- cluding higher instrumentality and lower expressiveness. However, these earlier studies differed from the current one in a number of ways. One study preselected par- ticipants on handedness (Nicholls & Forbes, 1996), an- other used a nonstandard measure of handedness (Casey & Nuttall, 1990), and various studies used different measures of gender-related traits (e.g., Coren, 1994; Santhakumari et al., 1994).This study is thefirst toassess various kinds of gender-related traits in the same large samples of men and women. As a result, the current data are probably the most complete to date on links between handedness and various kinds of gender-related personal- ity traits.

REFERENCES

Bem, S. L. (1981). Bem Sex-Role Inventory professional manual. Palo Alto, CA: Consulting Psychologists Press.

Blanchard, R. (1997). Birth order and sibling sex ratio in homosexual versus heterosexual males and females. Annual Review of Sex Re- search, 8, 27–67.

Blanchard, R., & Freund, K. (1983). Measuring masculine gender iden- tity in females. Journal of Consulting and Clinical Psychology, 51, 205–214.

Blanchard, R., & Klassen, P. (1997). H-Y antigen and homosexuality in men. Journal of Theoretical Biology, 185, 373–378.

Bryden,M.P.,McManus,I.C.,&Bulman-Fleming,M.B.(1994).Evalu- atingempiricalsupportfortheGeschwind-Behan-Galaburdamodel of cerebral lateralization. Brain and Cognition, 26, 103–165.

Cantor, J. M., Blanchard, R., Paterson, A. D., & Bogaert, A. F. (2002). How many gay men owe their sexual orientation to fraternal birth order? Archives of Sexual Behavior, 31, 63–71.

Casey, M. B., & Nuttall, R. L. (1990). Differences in masculine and feminine characteristics in women as a function of handedness: Support for theGeschwind/Galaburda theoryofbrainorganization. Neuropsychologia, 28, 749–754.

Coren,S.(1994).Personalitydifferencesbetweenleft-andright-handers: Anoverlookedminoritygroup?Journal of Research in Personality, 28, 214–229.

Coren, S., & Halpern, D. F. (1991). Left-handedness: A marker for de- creased survival fitness. Psychological Bulletin, 109, 90–106.

Coren, S., & Searleman, A. (1990). Birth stress and left-handedness: The rare trait marker model. In S. Coren (Ed.), Left-handedness: Behavioral implications and anomalies (pp. 3–32). Amsterdam: Elsevier.

P1: IZO Archives of Sexual Behavior pp744-aseb-460154 February 3, 2003 12:24 Style file version July 26, 1999

114 Lippa

Ellis, L., & Cole-Harding, S. (2001). The effects of prenatal stress, and of prenatal alcohol and nicotine exposure, on human sexual orien- tation. Physiology and Behavior, 74, 213–226.

Gangestad, S. W., Yeo, R. A., Shaw, P. K., Thoma, R., Daniel, W. F., & Korthank, A. (1996). Human leukocyte antigens and hand prefer- ence: Preliminary observations. Neuropsychology, 10, 423–428.

Geschwind, N., & Galaburda, A. M. (1985). Cerebral lateralization. Biological mechanisms, associations, and pathology: II. A hypoth- esis and a program for research. Archives of Neurology, 42, 521– 552.

Green,R.,&Young,R. (2001).Handpreference, sexualpreference, and transsexualism. Archives of Sexual Behavior, 30, 565–574.

Grimshaw, G. M., Bryden, M. P., & Finegan, J. K. (1995). Relations betweenprenataltestosteroneandcerebrallateralizationinchildren. Neuropsychology, 9, 68–79.

Haddock, C. K., Rindskopf, D., & Shadish, W. R. (1998). Using odds ratios as effect sizes for meta-analysis of dichotomous data: A primer on methods and issues. Psychological Methods, 3, 339– 353.

James,W.H.(1989).Foetal testosteronelevels,homosexualityandhand- edness: A research proposal for jointly testing Geschwind’s and Dörner’s hypotheses. Journal of Theoretical Biology, 136, 177– 180.

Lalumière, M. L., Blanchard, R., & Zucker, K. J. (2000). Sexual orien- tation and handedness in men and women: A meta-analysis. Psy- chological Bulletin, 126, 575–592.

Lippa, R. (1995). Gender-related individual differences and psycholog- ical adjustment in terms of the Big Five and circumplex models. Journal of Personality and Social Psychology, 69, 1184–1202.

Lippa, R. A. (2000). Gender-related traits in gay men, lesbian women, and heterosexual men and women: The virtual identity of homosexual–heterosexual diagnosticity and gender diagnosticity, Journal of Personality, 68, 899–926.

Lippa,R.A. (2001).Ondeconstructingand reconstructingmasculinity– femininity. Journal of Research in Personality, 35, 168–207.

Lippa, R. A. (2002a). Gender, nature, and nurture. Mahwah, NJ: Erlbaum.

Lippa, R. A. (2002b). Gender-related traits of heterosexual and homo- sexual men and women. Archives of Sexual Behavior, 31, 83–98.

Lippa, R., & Connelly, S. C. (1990). Gender diagnosticity: A new Bayesian approach to gender-related individual differences. Jour- nal of Personality and Social Psychology, 59, 1051–1065.

Lippa,R.A.,&Tan,F.D.(2001).Doesculturemoderate therelationship between sexual orientation and gender-related personality traits? Cross-Cultural Research, 35, 65–87.

Mustanski, B. S., Bailey, J. M., & Kaspar, S. (2002). Dermatoglyphics, handedness, and sexual orientation. Archives of Sexual Behavior, 31, 113–122.

Nicholls, M. E. R., & Forbes, S. (1996). Handedness and its association with gender-related psychological and physiological characteris- tics. Journal of Clinical and Experimental Neuropsychology, 18, 905–910.

Perelle, I. B., & Ehrman, L. (1994). An international study of human handedness: The data. Behavior Genetics, 24, 217–227.

Previc, F. H. (1996). Nonright-handedness, central nervous system and related pathology, and its lateralization: A reformulation and syn- thesis. Developmental Neuropsychology, 12, 443–515.

Santhakumari, K., Kurian, G., & Rao, V. K. (1994). Cross-gender iden- tity, familial nonright-handedness and hand preference. Psycholo- gia, 37, 34–38.

Satz, P. (1972). Pathological left-handedness: An explanatory model. Cortex, 8, 121–135.

Seddon, B. M., & McManus, I. C. (1991). The incidence of left- handedness: A meta-analysis. Unpublished manuscript. Depart- ment of Psychology, University College London, London.

Storms, M. D. (1979). Sex role identity and its relationship to sex role attributions and sex role stereotypes. Journal of Personality and Social Psychology, 37, 1779–1789.

Yeo, R. A., & Gangestad, S. W. (1998). Developmental instability and phenotypic variation in neural organization. In N. Raz (Ed.), The other side of the error term (pp. 1–51). New York: Elsevier.

Zucker,K.J.,Beaulieu,N.,Bradley,S.J.,Grimshaw,G.M.,&Wilcox,A. (2001). Handedness in boys with gender identity disorder. Journal of Child Psychology and Psychiatry, 42, 767–776.

Reproducedwithpermissionofthecopyrightowner.Furtherreproductionprohibitedwithoutpermission.