Information about scientific research

discussed on the Tyra Banks "Gaydar" program

The Tyra Banks TV program on "Gaydar" discussed a number of physical and psychological traits that are related to  sexual orientation. Among these are: finger-length ratios (the ratio of index finger length to ring finger length), handedness (whether a person is right or non-right-handed), hair whorl patterns (whether a man has a clockwise or counterclockwise hair whorl ), interests (the degree to which a person is interested in masculine vs. feminine occupations and hobbies), nonverbal behaviors (a person's style of movement and talking), and childhood behaviors (how masculine or feminine a person is as a child).  The following sections briefly summarize recent scientific research on these topics and list selected references to published studies.

Although the Tyra Banks Show included an entertaining demonstration of the physical and psychological traits possessed by three gay men and three straight men, this demonstration did not constitute a rigorous or controlled scientific study. The six participants in the Tyra Banks Show were selected by the show's staff, and the "sample size" was very small.  Actual scientific studies would have assessed larger and more diverse groups of people and they would have tested them under more controlled circumstances. Nonetheless, the traits and behaviors discussed on the Tyra Banks Show illustrate some of the traits and behaviors that have been studied in recently published scientific research.

Here's a summary of some relevant research on gay-straight differences:

Finger-length ratios:

Look at the palm your hand and observe the lengths of your index finger (the first finger, next to your thumb) and your ring finger (the finger next to your little finger; finger lengths are measured from the crease at the base of the finger to the tip of the finger).  In many people, these two fingers are different in length. For men,  the ring finger tends, on average, to be a bit longer than the index finger. In contrast, for women, the two fingers tend, on average,  to be about equal in length or the index finger tends to be a bit longer than the ring finger. Different finger length patterns in men and women may be related to prenatal differences in male and female hormone levels--particularly, levels of androgens like testosterone, which tend to be much higher in male than female fetuses. 

In recent years, a number of studies have investigated whether gay men and straight men and whether lesbian women and straight women differ in their finger-length ratios.  Some of these studies have suggested that gay men, on average, have more "female-like" finger-length ratios, and some have suggested that lesbians have more "male-like" ratios. These results suggest, to some researchers, that prenatal hormone levels may be one factor that influences adult sexual orientation. The findings on sexual orientation and finger-length ratios, however, are inconsistent and research on this topic is still somewhat unsettled.

It is important to note that male-female differences and heterosexual-homosexual differences in finger-length ratios tend to be small, and you need to look at many participants to see reliable differences.  (In one study that I published on this topic,  my research assistants and I assessed over 2000 men and women!)  Findings on heterosexual-homosexual differences in finger length ratios are theoretically interesting because they point to factors (such as prenatal hormones) that may be related to sexual orientation.  However, in practical terms, you cannot reliably tell a person's sexual orientation (or, for that matter, whether a person is male or female) based on his/her finger length ratios.

For more information, see the following articles:

Lippa, R. A. (2003). Are 2D:4D finger-length ratios related to sexual orientation? Yes for men, no for women. Journal of Personality and Social Psychology, 85, 179-188.

Manning, J. T., Churchill, A. J. G., & Peters, M. (2007). The effects of sex, ethnicity, and sexual orientation on self-measured digit ratio (2D:4D). Archives of Sexual Behavior, 36, 223-233.

Handedness:

Many studies suggest that gay and lesbian individuals show higher rates of non-right-handedness (i.e., higher rates of being left-handed or ambidextrous) than heterosexual men and women do.  Intriguingly, men also show consistently higher rates of non-right-handedness than women do.  In a paper published in 2000, Martin Lalumière, Ray Blanchard, and Ken Zucker compiled results from many previous studies on handedness and sexual orientation. Their compilation included handedness data from 6,182 gay men,  14,808 heterosexual men, 805 lesbian women, and 1,615 heterosexual women.  Their conclusion: Gay men had 34% greater odds of being non-right-handed than straight men did, and lesbians had 91% greater odds of being non-right-handed than heterosexual women did.  Recent research suggests that bisexual men and women report particularly high levels of ambidextrous hand preferences.  Studies published since 2000 continue to confirm Lalumière, Blanchard, and Zucker's basic conclusions: Although the exact rates of non-right-handedness vary from study to study, most studies find that rates of non-right-handedness are higher among gay men and lesbian women than among heterosexual men and women.

The reasons for heterosexual-homosexual differences in handedness are not clear.  There are a number of different theories that attempt to explain these differences.  Some focus on the effects of sex hormones and some focus on “developmental instability” before birth.  According to the sex hormone theory, variations in male hormone levels early in development influence both handedness and sexual orientation. The sex hormone theory might help explain why there are both sex differences and sexual orientation differences in handedness.  According to developmental instability theory, prenatal factors such as exposure to infectious diseases and environmental chemicals can perturb early brain development, and this can sometimes lead to unusual outcomes, such as left handedness and homosexuality.  Additional research is needed to test among these and other theories.

For more information, see the following articles:

Blanchard, R. and Lippa, R. A. (2007). Birth order, handedness, and sexual orientation of male and female participants in a BBC Internet research project. Archives of Sexual Behavior, 36, 163-176.

Lalumière, M. L., Blanchard, R., & Zucker, K. J. Sexual orientation and handedness in men and women: A meta-analysis. Psychological Bulletin, 126, 575-592.

Lippa, R. A. (2003). Handedness, sexual orientation, and gender-related personality traits in men and women. Archives of Sexual Behavior, 32, 103-114.

Hair Whorl Patterns:

Most people have hair whorls at the back of their heads (click here to see a photographic illustration). That is, most people have little "whirlpools" of hair, that curl in either a clockwise or counterclockwise direction.  Hair whorls are easier to see and measure in men than in women, because men tend to have shorter hair than women (at least, in the United States).  If you have a cowlick--a bit of hair in the back of your head that sticks out in an unruly fashion and is hard to comb and style--it may be because of the position of the hair whorl at the back of your head.  A small number of people (say, 3 or 4 percent) have more than one hair whorl at the back of their heads--some people with two hair whorls have both a clockwise and a counterclockwise hair whorl. 

Previous research suggests that in most people (about 90% or more of the population), hair whorls curl in a clockwise direction, whereas in a minority of people (8% to 10%) hair whorls curl in a counterclockwise direction.  Interestingly, this ratio (about 9 to 1), is similar to the ratio of right-handed to non-right-handed people. Indeed, some recent theories propose the existence of hypothetical genes that are responsible for both handedness and hair whorl direction.  If these theories are correct, then left-handed people should have a higher rates of counterclockwise hair whorls than right-handed people.  Ultimately, handedness and hair whorl patterns are related to lateralization of the brain (lateralization refers to the fact that the right and left halves of the human brain develop somewhat differently and have somewhat different functions--e.g., the left half is often more responsible for language processing, whereas the right half is more responsible for certain kinds of visual-spatial abilities and pattern recognition).

Biologist Amar Klar published an observational study in 2003 suggesting that gay men have a higher rate of counterclockwise hair whorls than straight men do.  A number of researchers, including myself, are attempting to replicate Klar's findings.  Based on data I have collected from over 500 gay men in southern California and from hundreds of straight men (college men; men observed in public settings, like shopping malls), I have concluded that about 20% of gay men have counterclockwise hair whorls, whereas about 10% of straight men and men in general have counterclockwise hair whorls.  Thus, it appears that the rate of counterclockwise hair whorls is about twice as large in gay men as in straight men. Additional research is needed to replicate these results and to determine the theoretical implications of these findings. 

At the very least, a reliable association between hair whorl patterns and sexual orientation suggests that there are biological factors linked to sexual orientation, because people are born with their hair whorl patterns and it seems unlikely that hair whorl patterns result from learning or cultural factors.  (In contrast, handedness can be affected, to some degree, by learning and cultural factors.)

An important caveat: Even if it is true that the rate of counterclockwise hair whorls is reliably higher in gay men than in straight men, this does not mean you can accurately tell a man's sexual orientation from his hair whorl pattern.  Most men--both gay and straight--have clockwise hair whorls.  Furthermore, there are a lot more straight men than gay men in the general population.  Thus, if you see a man with a counterclockwise hair whorl, chances are that he's straight, even though the rate of counterclockwise hair whorls appears to be somewhat higher in gay men than in straight men.

For more information, see the following article (and expect a lot more studies to be published on this topic in the near future):

Klar, A. J. S. (2004). Excess of counterclockwise scalp hair-whorl in homosexual men. Journal of Genetics, 83, 251-255.

 Gender-Related Interests:

Over the past 20 years, a lot of my research has focused on people's interests (e.g., their occupational and hobby preferences) and how such interests differ in men and women and in gay and straight people.  Whereas gender differences and gay-straight in physical traits (like finger-length ratios and hair whorl patterns) are fairly small, gender and sexual orientation differences in interests are quite large.  Many studies suggest that women tend to be more interested in "people oriented" occupations, hobbies, and activities, whereas men tend to be more interested in "thing oriented" occupations, hobbies, and activities.  (Examples of "people oriented" occupations are social worker, teacher, manager; examples of "thing oriented" occupations are mechanic, engineer, computer programmer.)  The difference between women and men is quite large on this dimension. In one set of studies, I estimated that about 90% of women are more "people oriented" in their interests and occupational preferences than the average man is.  Similarly, about 90% of men are more "thing oriented" in their interests and occupational preferences than the average woman is. Statisticians consider differences of this magnitude to be very large.

Heterosexual and homosexual individuals also show on-average differences in their interests, and these differences mirror male-female differences. Specifically, gay men tend to have considerably more female-typical, "people oriented" interests than straight men do, and lesbians tend to have considerably more male-typical, "thing oriented" interests than straight women do.  Combining results from eight studies on this topic, I found that 90% of gay men had more "people oriented" interests and occupational preferences than the average heterosexual man did.  Similarly,  93% of lesbians had more masculine, "thing oriented" interests and occupational preferences than the average heterosexual woman did.   

Note: Even though male-female differences and heterosexual-homosexual differences in interests are large, they are still just on-average differences, and there are lots of exceptions.  As a comparison, consider differences in men's and women's height.  Most men are taller than most women, and the on-average difference in men's and women's height is quite large.  Nonetheless, there are many short men and many tall women.  Similarly, there are heterosexual women and gay men who are interested in being engineers and computer programmers, and there are heterosexual men and lesbian women who are interested in being social workers and elementary school teachers.  At the same time, there are large on-average differences in the interests of men and women and in the interests heterosexual and homosexual individuals. 

Because of this this, you would tend to do a much better job guessing a person's sex (male or female) or sexual orientation (heterosexual or homosexual) based on his or her  interests than you would based on physical traits like finger length ratios or hair whorl patterns. Indeed, when judging whether each of the six men participating in the Tyra Banks Show was straight or gay, I mentally "weighted" information about the men's interests, nonverbal behaviors, and childhood behaviors much more strongly than I weighed traits like finger-length ratios, hair whorl patterns, and handedness.  The reason is simple: Research shows that interests, nonverbal behaviors, and childhood behaviors are much more strongly related to sexual orientation than are physical traits like finger-length ratios and hair whorl patterns.

For more information, see the following books, articles, and chapters:

Lippa, R. (1998). Gender-related individual differences and the structure of vocational interests: The importance of the "People-Things" dimension. Journal of Personality and Social Psychology, 74, 996-1009.

Lippa, R. A. (2005).  Sexual orientation and personality.  Annual Review of Sex Research, 16, 119-153.

Lippa, R. A. (2005). Gender, Nature, and Nurture (2nd ed.). Lawrence Erlbaum Associates.

Lippa, R. A. (2005). Sex and gender. In V. J. Derlega, B. A. Winstead, & W. H. Jones (Eds.), Personality: Contemporary theory and research (3rd ed., pp. 332-365). Belmont, CA: Wadsworth.

Lippa, R. A. (in press).  Sex differences and sexual orientation differences in personality: Findings from the BBC Internet survey, Archives of Sexual Behavior.

Nonverbal behavior.

Men and women show large on-average differences in many kinds of nonverbal behaviors (see my 2005 book, Gender, Nature, and Nurture, for a review). For example, on average, women tend to smile more and engage in more eye contact than men do when interacting with others.  Women also tend to be more facially expressive than men.  Men tend to maintain more "body space" than women do (i.e., they don't approach others as closely; their gestures are more expansive; they take up more space, for example, when they sit in chairs; they hold their legs apart at larger angles and hold their arms away from their body at larger angles than women do).  On average, men's speech contains more "nonfluencies" than women's speech does--stutters, stammers, "ah's," "er's" and "um's."  Other aspects of male and female speech also differ, including voice pitch, enunciation, and expressiveness.

Increasingly, recent research has shown that heterosexual and homosexual people differ, on average, in their nonverbal behaviors, and some of these differences mirror male-female differences.  For example, when walking, gay and lesbian individuals differ from same-sex heterosexuals in their degree of shoulder swagger (a male-typical behavior) and in their degree of hip sway (a female-typical behavior; see the Johnson, Gill, Reichman, & Tassinary, 2007, reference below).  Past studies have shown that lay people can accurately judge whether target individuals are heterosexual or homosexual at levels exceeding chance, even after viewing very brief (e.g., just a few seconds long) videotapes of targets (Ambady, Hallahan, & Conner, 1999). Some studies suggest that the voice quality of gay men and straight men differs, on average, with gay men's speech often perceived as having more feminine qualities than straight men's speech (Gaudio, 1994). 

Although more research needs to be done on this topic, it is likely that some heterosexual-homosexual differences in nonverbal behaviors are large.  Once again, it is important to emphasize that the existence of on-average differences does not mean that all gay men talk and move in "feminine" ways or that all lesbians talk and move in "masculine" ways.  Rather, it means is that there are on-average, statistically significant differences between heterosexual and homosexual individuals.  Undoubtedly, there are many gay men and lesbian women who "look straight" and, similarly, there are some heterosexual men and women who are perceived to be homosexual.

For more information, see the following articles:

Ambady, N., Hallahan, M., & Conner, B. (1999). Accuracy of judgments of sexual orientation from thin slices of behavior. Journal of Personality and Social Psychology, 77, 538-547.

Gaudio, R. (1994). Sounding gay: Pitch properties in the speech of gay and straight men. American Speech, 69, 30-57.

Johnson, K. L., Gill, S., Reichman, V., & Tassinary, L. G. (2007). Swagger, sway, and sexuality: Judging sexual orientation from body motion and morphology.  Journal of Personality and Social Psychology, 93, 321-334.

Childhood behaviors: Childhood gender conformity and nonconformity.

Perhaps the strongest, most replicated finding in the "psychology of sexual orientation" is that there is a strong link between childhood gender conformity-nonconformity and adult sexual orientation.  (Childhood gender conformity occurs when children behave in ways typical of their own sex. Childhood gender nonconformity occurs when children behave in ways that are more typical of the other sex.  For example, if a boy likes to play with trucks and "G.I. Joe" dolls, likes competitive team sports, hangs out mostly with other boys, and is considered by his friends and family to be masculine, then he is behaving in gender conforming ways.  On the other hand, if a boy likes to play with Barbie dolls and baby dolls, dislikes competitive team sports, hangs out with girls more than boys, and is considered by his friends and family to be something of a "sissy," then he is behaving in gender nonconforming, girl-typical ways.)

In a review of 41 studies on "childhood sex-typed behavior" (whether children behave in ways that are typical or atypical of their sex) and sexual orientation, Michael Bailey and Ken Zucker (1995) found a strong relationship between childhood gender conformity-nonconformity and sexual orientation.  Adult homosexuality is strongly associated with childhood gender nonconformity, and adult heterosexuality is strongly associated with childhood gender conformity.  The summary statistics presented in Bailey and Zucker's review imply that about 90% of gay men reported more "feminine," gender-nonconforming childhood behavior than the average heterosexual man did, and about 83% of lesbian women reported more "masculine," gender-nonconforming childhood behavior than the average heterosexual woman did. Statisticians consider differences of this magnitude to be large.

The link between childhood gender conformity-nonconformity and adult sexual orientation has been replicated in many studies conducted since Bailey and Zucker's 1995 review.  Indeed, the finding that childhood gender nonconformity "goes along with" adult homosexuality and that childhood gender conformity "goes along with" adult heterosexuality can be considered almost a "never fail" finding. The link between childhood gender conformity-nonconformity and adult sexual orientation is among the strongest associations that psychologists have ever documented between a childhood trait and an adult trait.

The fact that there are childhood behaviors that are strongly linked to adult sexual orientation and the fact that these childhood behaviors are clearly apparent long before adult sexuality has developed is consistent with the hypothesis that there are biological factors (e.g., variations in prenatal exposure to sex hormones) that influence both gender-related behaviors in childhood and sexual orientation later in life. 

Recently, researchers have begun to study children's nonverbal masculinity-femininity and adult sexual orientation by looking at childhood videos of gay and straight volunteers (e.g., Rieger, Linsenmeier, Gygax, & Bailey, in press).  Once again, these studies find strong links between childhood masculinity-femininity and adult sexual orientation.  Boys who become gay men are judged to be more feminine and gender nonconforming as children than are boys who become straight men, and girls who become lesbians are judged to be more masculine and gender nonconforming as children than are girls who become straight women.

For more information, see the following articles:

Bailey, J. M., & Zucker, K. J. (1995). Childhood sex-typed behavior and sexual orientation: A conceptual analysis and quantitative review. Developmental Psychology, 31, 43-55.

Rieger, G., Linsenmeier, J. A. W., Gygax, L., & Bailey, J. M. (in press). Sexual orientation and childhood sex atypicality: Evidence from home movies. Child Development.

This completes this brief summary
of research on gay-straight differences.
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in ongoing research on personality traits, interests, and sexuality
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on "sexual attitudes, personality, and interests"!