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Males Do Not Reduce the Fitness of Their Female Co-Twins in Contemporary Samples

Published online by Cambridge University Press:  21 February 2012

Sarah E. Medland ,
John C. Loehlin ,
Gonneke Willemsen ,
Peter K. Hatemi ,
Mathew C. Keller ,
Dorret I. Boomsma ,
Lindon J. Eaves  and
Nicholas G. Martin
Sarah E. Medland*
Affiliation:
Genetic Epidemiology Unit, Queensland Institute of Medical Research, Australia; Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, United States of America. [email protected]
John C. Loehlin
Affiliation:
University of Texas, United States of America.
Gonneke Willemsen
Affiliation:
Vrije Universiteit Amsterdam, the Netherlands.
Peter K. Hatemi
Affiliation:
Genetic Epidemiology Unit, Queensland Institute of Medical Research, Australia; Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, United States of America.
Mathew C. Keller
Affiliation:
University of Colorado, United States of America.
Dorret I. Boomsma
Affiliation:
Vrije Universiteit Amsterdam, the Netherlands.
Lindon J. Eaves
Affiliation:
Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, United States of America.
Nicholas G. Martin
Affiliation:
Genetic Epidemiology Unit, Queensland Institute of Medical Research, Australia.
*
*Address for correspondence: Sarah Medland, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, Box 980126 MCV, Richmond VA 23298.

Abstract

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Lummaa et al. (2007) presented historical data collected from twins born in Finland between 1734 and 1888 which suggested that females (N = 31) born as part of an opposite sex (OS) twin pair were 25% less likely to reproduce than female twins (N = 35) born as part of a same sex (SS) pair. They hypothesized that this reduction in fitness was due to masculinization of the female fetus via prenatal effects of the hormones of a male fetus. Because such masculinization would presumably take place in modern populations as well, it would seem important to establish to what degree it does so, and if so, whether reproduction is affected. We therefore address the question of reproduction differences in individual female twins from same-sex (N = 1979) and opposite-sex (N = 913) dizygotic pairs in studies carried out in Australia, the Netherlands, and the United States. In all three samples, there were no differences in the number of children or age of first pregnancies in women from same sex pairs compared to those from opposite sex pairs. Similarly, there were no differences in psychological femininity between women from pairs of the same or opposite sex.

Keywords

fertilityhormone transfertwinning
Type
Articles
Information
Twin Research and Human Genetics , Volume 11 , Issue 5 , 01 October 2008 , pp. 481 - 487
Copyright
Copyright © Cambridge University Press 2008