The dynamics of the level of sexual dimorphism of somatic traits through the 8-17 age period
The introduction includes the discussion of the hypothesis of independent direction of somatic variation between two sexes. The results of the Deryabin’ study of body composition of adults are cited, illustrating the fact that andro-ginecomorphy is not the independent intergroup conformity of continuous body composition variation, but is the atribute of intragroup variation. The main aim of the present work is the analysis of sexual dimorphism of 8-17 year old children using a set of somatic parameters and the method after Kullback. The value of Kullback distance for different traits are quantities, expressed in the parts of their standard deviations, thus they are completely comparable for the whole lot of body dimensions with different units, absolute size and the degree of intragroup variability. To get the lines of sexual dimorphism dynamics for different traits we used 4 data sets of Moscow school children: 1) longitudinal data 1982-91, collected by Yampolskaya, quantized by Fedotova while preparing the common monograph [Deryabin et al., 2006]; 2) The longitudinal data 1960-69, literary data [Vlastovsky et al., 1977]; 3) longitudinal/crosssectional data 1968-72, literary data [Solovieva et al., 1977]; 4) crosssectional data 1996-99, literary data [Godina et al., 2003]. The common picture of the age changes of the sexual dimorphism value through 8-16 year interval for the major part of traits - body length and mass, the longitudinal parameters of the trunk and the leg, biacromial and pelvic diameters - may be approximately described by the parabola of 4th parabola with 3 bend points. The first point is viewed at the end of second childhood for boys and the beginning of puberty for girls, when the acceleration of their development leads to the change of the direction of sexual differences. The second point is viewed during the first phase of pubertal period, when boys have more intensive growth processes which leads to abolishing of the effect of the first growth curves cross and forming of the definite value of sexual dimorphism. The third point characterizes the beginning of the youth period when the intensity of sexual dimorphism growth decreases. The skinfolds have the different age dynamics of sexual differences. Through second childhood and the beginning of puberty the higher development of the traits belongs to the girls, the mean standardized level is 0.2-1.0. At the age of 12 the increase of the fat development in girls leads to the increase of sexual dimorphism, reaching at the age of 16-17 the levels of 0.8-2.2 standard deviations, which is close to the definite adults levels of the traits. The common pattern of age changes of the sexual dimorphism value through 8-16 years for skeletal and muscle traits is described by the parabola of 4th parabola with three bend points, connected with the differences of pubertal processes of two sexes. The skinflods are characterized by small values of sexual differences through second childhood and the beginning of puberty and gradual increase of the level from 12 years and forth till the definite adult levels in the youth. The total level of sexual dimorphism of the set of traits increases to 17 years up to the definite adult level.