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Hand asymmetry in heterosexual and homosexual men and women: relationship to 2D:4D digit ratios and other sexually dimorphic anatomical traits.
Arch Sex Behav. 2008 Feb; 37(1):119-32.AS

Abstract

Sexual differentiation leads to the development of distinctive anatomical structures (e.g., gonads and genitalia); it also produces less obvious anatomical shifts in brain, bones, muscles, etc. This study is a retrospective analysis of growth patterns in the hands in relation to sex and sexual orientation. Using data from three published studies, we analyzed four hand traits in adults: hand width, hand length, second digit length, and fourth digit length. Using these measurements, we derived estimates of trait laterality (directional asymmetry or DA) and developmental instability (fluctuating asymmetry or FA). High FA is a putative indicator of interference with the cellular and molecular mechanisms regulating development. We focused on how these derived variables were related to sex, sexual orientation, and putative markers of early sex steroid exposure (e.g., the second to fourth digit ratio or 2D:4D). Our data point to three principal conclusions. First, individual differences in DA appeared to be a major source of variation in the 2D:4D ratio. The 2D:4D ratios of heterosexual men differed depending on whether they had leftward or rightward DA in their digits. Homosexual women showed the same pattern. Individuals with leftward DA in both digits had lower 2D:4D ratios than those with rightward DA. This effect was absent in heterosexual women and homosexual men. This led to sex differences in 2D:4D and sexual orientation differences in 2D:4D in the leftward DA group, but not in the rightward DA group. The second conclusion was that DA in digit length and hand width varied with sex; women were more likely to have rightward asymmetry than men. Homosexual men and women were generally sex typical in DA. The third conclusion was that homosexuality is unlikely to be a result of increased developmental instability. Although limited in scope, the present evidence actually suggests that homosexuals have lower FA than heterosexuals, raising the question of whether the positive fitness components associated with low FA may contribute to selection that maintains homosexuality in a population.

Authors+Show Affiliations

Department of Basic Medical Sciences, College of Osteopathic Medicine of the Pacific, Western University of Health Sciences, 309 E. 2nd Street, Pomona, CA 91766, USA. jmartin@westernu.eduNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

18161017

Citation

Martin, James T., et al. "Hand Asymmetry in Heterosexual and Homosexual Men and Women: Relationship to 2D:4D Digit Ratios and Other Sexually Dimorphic Anatomical Traits." Archives of Sexual Behavior, vol. 37, no. 1, 2008, pp. 119-32.
Martin JT, Puts DA, Breedlove SM. Hand asymmetry in heterosexual and homosexual men and women: relationship to 2D:4D digit ratios and other sexually dimorphic anatomical traits. Arch Sex Behav. 2008;37(1):119-32.
Martin, J. T., Puts, D. A., & Breedlove, S. M. (2008). Hand asymmetry in heterosexual and homosexual men and women: relationship to 2D:4D digit ratios and other sexually dimorphic anatomical traits. Archives of Sexual Behavior, 37(1), 119-32.
Martin JT, Puts DA, Breedlove SM. Hand Asymmetry in Heterosexual and Homosexual Men and Women: Relationship to 2D:4D Digit Ratios and Other Sexually Dimorphic Anatomical Traits. Arch Sex Behav. 2008;37(1):119-32. PubMed PMID: 18161017.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Hand asymmetry in heterosexual and homosexual men and women: relationship to 2D:4D digit ratios and other sexually dimorphic anatomical traits. AU - Martin,James T, AU - Puts,David A, AU - Breedlove,S Marc, PY - 2007/12/28/pubmed PY - 2008/6/19/medline PY - 2007/12/28/entrez SP - 119 EP - 32 JF - Archives of sexual behavior JO - Arch Sex Behav VL - 37 IS - 1 N2 - Sexual differentiation leads to the development of distinctive anatomical structures (e.g., gonads and genitalia); it also produces less obvious anatomical shifts in brain, bones, muscles, etc. This study is a retrospective analysis of growth patterns in the hands in relation to sex and sexual orientation. Using data from three published studies, we analyzed four hand traits in adults: hand width, hand length, second digit length, and fourth digit length. Using these measurements, we derived estimates of trait laterality (directional asymmetry or DA) and developmental instability (fluctuating asymmetry or FA). High FA is a putative indicator of interference with the cellular and molecular mechanisms regulating development. We focused on how these derived variables were related to sex, sexual orientation, and putative markers of early sex steroid exposure (e.g., the second to fourth digit ratio or 2D:4D). Our data point to three principal conclusions. First, individual differences in DA appeared to be a major source of variation in the 2D:4D ratio. The 2D:4D ratios of heterosexual men differed depending on whether they had leftward or rightward DA in their digits. Homosexual women showed the same pattern. Individuals with leftward DA in both digits had lower 2D:4D ratios than those with rightward DA. This effect was absent in heterosexual women and homosexual men. This led to sex differences in 2D:4D and sexual orientation differences in 2D:4D in the leftward DA group, but not in the rightward DA group. The second conclusion was that DA in digit length and hand width varied with sex; women were more likely to have rightward asymmetry than men. Homosexual men and women were generally sex typical in DA. The third conclusion was that homosexuality is unlikely to be a result of increased developmental instability. Although limited in scope, the present evidence actually suggests that homosexuals have lower FA than heterosexuals, raising the question of whether the positive fitness components associated with low FA may contribute to selection that maintains homosexuality in a population. SN - 0004-0002 UR - https://www.unboundmedicine.com/medline/citation/18161017/Hand_asymmetry_in_heterosexual_and_homosexual_men_and_women:_relationship_to_2D:4D_digit_ratios_and_other_sexually_dimorphic_anatomical_traits_ L2 - https://doi.org/10.1007/s10508-007-9279-8 DB - PRIME DP - Unbound Medicine ER -