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Increased tooth crown size in females with twin brothers: Evidence for hormonal diffusion between human twins in utero
Author(s) -
Dempsey Paula J.,
Townsend Grant C.,
Richards Lindsay C.
Publication year - 1999
Publication title -
american journal of human biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.559
H-Index - 81
eISSN - 1520-6300
pISSN - 1042-0533
DOI - 10.1002/(sici)1520-6300(199909/10)11:5<577::aid-ajhb1>3.0.co;2-y
Subject(s) - sexual dimorphism , in utero , biology , hormone , hum , litter , endocrinology , medicine , fetus , physiology , pregnancy , genetics , art , performance art , agronomy , art history
In rodents, the position of a fetus in utero is associated with the expression of sexually dimorphic traits. This phenomenon has been explained by prenatal diffusion of sex hormones among litter mates. To test for such effects in humans, female‐male twin pairs provide a natural experiment. The size of dental crowns is a sexually dimorphic trait which can be measured with a high degree of reliability. Thus, two crown diameters of 28 permanent teeth were recorded for 56 opposite‐sexed (OS) and 242 same‐sexed (SS) twin pairs, and 150 singletons. Comparisons of OS twins with SS twins and singletons within each sex reveal that OS females have consistently larger teeth (on average) than other females, while there is no consistent difference between OS and SS twin males. It is proposed that diffusion of sex hormones from male to female co‐twins in utero may account for the increased tooth size in OS females. This study is one of the first to report such an effect on a morphological variable in humans. The finding that the maxillary canine, one of the most sexually dimorphic teeth, exhibits the least effect in OS female twins, suggests that prenatal sex hormone levels may have less impact on sexual dimorphism in the maxillary canines than in other permanent teeth. Am. J. Hum. Biol. 11:577–586, 1999. © 1999 Wiley‐Liss, Inc.