Isolation by Distance Between Spouses and its Effect on Boys’ Maturational Timing
Heterosis is thought to be an important contributor to human growth and development. Marital distance (distance between parental birthplaces) is commonly considered as a factor favoring the occurrence of heterosis and can be used as a proximate measure of its level. It has already been shown that marital distance appears to be an independent and important factor influencing the height of offspring. However, there is no study showing this effect on maturational timing in boys. The aim of the study was to assess the effect of marital radius on age at peak height velocity in boys, controlling for midparental height and the socioeconomic status of family. Longitudinal, annual height measurements on 740 boys from 11 to 15 years of age from Ostrowiec Świętokrzyski, Poland, were analyzed along with sociodemographic data from their parents. Midparental height was calculated as the average of the reported heights of the parents. The SITAR model was applied to the longitudinal data of height in order to assess the age at peak height velocity (APHV). As the measurements were incomplete, the APHV was successfully estimated in only 298 boys. Multiple Linear regression showed the small, but significant effect of Marital distance on the maturation rate of boys (standardized beta=-0.14; p<0.05). According to the ‘‘isolation by distance’’ hypothesis, a greater distance between parental birthplaces may increase heterozygosity, potentially promoting heterosis. We propose that these conditions may result in reduced metabolic costs of growth among heterozygous individuals, and hence a lowered velocity of growth.