title: Bonobos have a more human-like second-to-fourth finger length ratio (2D:4D) than chimpanzees: a hypothesized indication of lower prenatal androgens.
abstract: The ratio of the second-to-fourth finger lengths (2D:4D) has been proposed as an indicator of prenatal sex differentiation. However, 2D:4D has not been studied in the closest living human relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). We report the results from 79 chimpanzees and 39 bonobos of both sexes, including infants, juveniles, and adults. We observed the expected sex difference in 2D:4D, and substantially higher, more human-like, 2D:4D in bonobos than chimpanzees. Previous research indicates that sex differences in 2D:4D result from differences in prenatal sex hormone levels. We hypothesize that the species difference in 2D:4D between bonobos and chimpanzees suggests a possible role for early exposure to sex hormones in the development of behavioral differences between the two species.
authors.affiliation: Department of Anthropology, University of Central Florida, Orlando, FL 32816, USA. mmcintyr@mail.ucf.edu
authors.forename: Matthew H
authors.initials: MH
authors.lastname: McIntyre
authors.forename: Esther
authors.initials: E
authors.lastname: Herrmann
authors.forename: Victoria
authors.initials: V
authors.lastname: Wobber
authors.forename: Michel
authors.initials: M
authors.lastname: Halbwax
authors.forename: Crispin
authors.initials: C
authors.lastname: Mohamba
authors.forename: Nick
authors.initials: N
authors.lastname: de Sousa
authors.forename: Rebeca
authors.initials: R
authors.lastname: Atencia
authors.forename: Debby
authors.initials: D
authors.lastname: Cox
authors.forename: Brian
authors.initials: B
authors.lastname: Hare
mesh_terms: D000728:Androgens / Q000378:metabolism; D000818:Animals; D005260:Female; D005385:Fingers / Q000033:anatomy & histology*; D008297:Male; D019974:Pan paniscus / Q000033:anatomy & histology* / Q000378:metabolism; D002679:Pan troglodytes / Q000033:anatomy & histology* / Q000378:metabolism; D012727:Sex Characteristics
chemical_list: D000728:Androgens