Height and reproductive success: a longitudinal study of Finnish twins

Karri Silventoinen, University of Helsinki
Samuli Helle, University of Turku
Jessica Nisén, University of Helsinki
Pekka Martikainen, University of Helsinki
Jaakko Kaprio, University of Helsinki

Preference of females to the larger body size of males is common in primates and has probably contributed to sexual dimorphism in body size. There has been speculation, but no strong evidence so far, that the similar process would exist also in humans. Thus we decided to analyze height and reproductive success using a twin design, which allows optimally standardize for family background. Our data include Finnish twins (3595 male and 4235 female twin individuals) born in 1950-57. Information on height, education and living with a spouse were based on questionnaires in 1975 and 1981 and information on live births until June 2009 on the Finnish population register. Multinomial logistic regression was used in individual level analyses and conditional logistic regression to analyze within-pair associations. In the individual level analyses in males, the highest probability to have 1-2 children was in the third sex-specific height quintile, and it decreased slightly when adjusting for education and living with a spouse when compared to males having no children and to the lowest height quintile. When analyzing the probability to have 3 children or more, the tallest and third quintiles showed the highest probabilities, but these associations were not anymore statistically significant when education and living with a spouse were adjusted for. When analyzing pair-wise associations in male twins, the probability to have 1 child or more was highest in the third quintile and this association decreased slightly when education and living with a spouse were adjusted for. In women no associations between height and reproduction were found in individual level or in pair-wise twin analyses. Our results do not support the hypothesis that tall stature is associated with higher reproductive success but rather that average stature may give some advantage for reproduction in males.