Sexual dimorphism in newborns and adults

A total of 1034 newborns were used to analyze sexual dimorphism with respect to 37 somatic traits and ratios between them, describing body shape. Arithmetic means and standard deviations were calculated for both sexes. Similarly, sexual dimorphism of adults was analyzed. Sexual differences in newborns were statistically significant for most measurements but only for some body proportions (relative chest size, foot shape, relative lower extremity length, and the ratio of head to chest circumference). The highest degree of sexual dimorphism in newborns was shown by the index standardized on the mean (dsex/mean) of such traits as the thickness of subcutaneous fat tissue on the thigh, subscapular fat tissue and fat tissue on the 10th rib, body weight, hand breadth, and relative chest size (Marty index). A moderate dimorphism was found for the length of upper extremities, forearm with the hand, head with the neck, hand and trunk, the size of the nose and foot, the breadth of hips and mandible, and the upper-face height. A low dimorphism was found for body length, circumference and breadth of head, face diameter, chest circumference, foot shape, relative length of lower extremities, and proportion between head and chest circumferences. Sexual differences (dsex/mean) for all the somatic traits examined in adults were statistically significant. The dimorphism of all the traits (except hip breadth) was higher in adults than in newborns. The highest increase in sexual dimorphism was noted for chest breadth (ca 55 times), then for chest depth (ca 17 times), thickness of subcutaneous fat tissue on arm (ca. 17 times), and the length of lower extremities (ca 15 times). Sexual differences in proportions (shape) of the body were also better pronounced in adults than in newborns. Sexual dimorphism standardized for dispersion (dsex/SD) in newborns differed from that in adults with respect to the degree of its expression and the sequence of the traits showing the highest and the lowest levels of dimorphism. This results from intra-group variation of different traits.