Does a seasonal developmental rhythm exist in tropical living populations?

The main aim of this work concerns the answer a question whether the general regularity of seasonal differences in changes of height, weight and body components during ontogeny exist. If so, whether this phenomenon depends on cyclic changes in nature or this rather is an adjustment to local conditions and mode of life. To answer this question the studies took place in the tropical climate of Yucatan and included 49 boys and 47 girls aged 11-12 years and being of the Maya, Mestizo and Creole origin. The youths were attending two schools which were located in rather poor districts of Merida (capital city of the Yucatan State, Mexico). The investigations started in February 2002 and ended in November 2003 and were continued monthly. The standard anthropometric methodology was applied to measure body height, weight, arm, waist, hip and calf circumferences and five subcutaneous fat folds (biceps and triceps brachii, subscapular, suprailiac and calf). Bioimpedance techniques were used to measure fat mass (FM), fat free mass (FFM) and total body water (TBW). The results show that monthly or longer rates of stature increments and increments or declines of body mass do not exist. The similar observations were mentioned according to daily studies of similar type in literature. There are not similar regularities of changes even in groups of coevals of the same gender and within the youths coming from the same district. Each variable shows a quite specific rate of changes.