Until 2006, samples from more than 25 different countries or ethnic groups were collected and investigated, but the participants were mainly White (Voracek & Dressler, 2006). As Voracek and Dressler ( 2006) discussed, these differences are poorly understood and, therefore, cross-cultural studies concerning 2D:4D are still interesting. Surprisingly, 2D:4D varies across nations and these cross-national differences are noticeably larger than the sex differences found within nations (Manning, Churchill, et al., 2007 Manning et al., 2000, 2003, 2004). This example shows that different results regarding 2D:4D might be obtained and further comparative studies regarding this issue are necessary.Īnother poorly investigated issue concerns cross-racial differences in sexual dimorphism of 2D:4D. Additionally, ethnicity explained some between-studies variation in men. The latest meta-analysis regarding 2D:4D and sexual orientation (Grimbos, Dawood, Burriss, Zucker, & Puts, 2010) showed that there was no difference between heterosexual and gay men (but heterosexual women had more feminine 2D:4D than did lesbians). For example, some studies investigating relations between finger digit ratios and sexual orientation reported that homosexual men have higher 2D:4D than heterosexual men (Manning, Churchill, & Peters, 2007 McFadden & Shubel, 2002), some that homosexual men have lower 2D:4D than heterosexual men (Rahman, 2005 Rahman & Wilson, 2003), and other that there is no significant difference between 2D:4D in homo- and heterosexual men (Voracek, Manning, & Ponocny, 2005 Williams et al., 2000). On the other hand, results regarding other variables were less homogenous. For example, many studies showed that low 2D:4D ratios correlated with athletic ability (Manning, Morris, & Caswell, 2007 Manning & Taylor, 2001) and male aggression (Bailey & Hurd, 2005 McIntyre et al., 2007). 2D:4D was shown to be a correlate of a multitude of sex-dependent, hormonally influenced variables such as behavioral, cognitive, personality, and somatic traits, adult-onset disorders, and measures related to fertility and sexuality (for review, see Manning, 2002). Over the past few years, this hypothesis has generated much interdisciplinary research interest (for review, see Gallup et al., 2008 Voracek & Loibl, 2009). Because of the early fetal development of sexual dimorphism in 2D:4D, it is suggested that 2D:4D may serve as a biomarker for prenatal androgen exposure (Gallup, Frederick, & Pipitone, 2008 Lutchmaya, Baron-Cohen, Raggatt, Knickmeyer, & Manning, 2004 Manning et al., 1998). Males develop a lower 2D:4D than females by the end of the first trimester of gestation (Galis, Ten Broek, Van Dongen, & Wijnaendts, 2010 Malas, Dogan, Evcil, & Desdicioglu, 2006). Therefore, the ratio between the length of second and fourth manual digits (2D:4D) is a sexually dimorphic trait-males tend to have lower 2D:4D values that females (Ecker, 1875 George, 1930, Manning, Scutt, Wilson, & Lewis-Jones, 1998) and it seems to be a cross-cultural trait (Manning, Henzi, Venkatramana, Martin, & Singh, 2003 Manning, Stewart, Bundred, & Trivers, 2004 Manning et al., 2000). Estrogen exposure has the opposite effect the index finger tends to be longer than the ring finger. People exposed to elevated levels of testosterone tend to have ring fingers (the fourth digit: 4D) longer than their index fingers (the second digit: 2D). At the same time, masculine (physically strong, dominant, and hardworking) males might gather resources necessary to marry their first wife earlier.Įxposure to different levels of sex hormones in utero leaves effects on human fingers. We suggest that mating preferences for females with masculine 2D:4D are related to masculinity of phenotypic and personality traits of such women, which are beneficial in harsh environmental conditions and/or higher facial masculinity, which influences the perceived age of an individual. Females and males with a more masculine 2D:4D were married earlier and were more likely to have a husband or wife. The 2D:4D ratio did not correlate with number of children. As found in the majority of previous studies, males had lower 2D:4D ratios than females. 2D:4D ratios were calculated for a sample of this population ( N = 99 60 women, 39 men), and the results were correlated with age, marital status, age at first marriage, number of children, and number of marriages. Here, we present a study conducted among the semi-nomad Himba population living in northern Namibia. However, direct association between 2D:4D and reproductive success-in populations where no contraceptives are used-has not been investigated. It is associated with many behavioral and biological variables, including fertility and sexual behavior. The second to fourth digit ratio (2D:4D) is used as a potential marker for prenatal androgen exposure.
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