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Human body size and body proportions are interpreted as markers of ethnicity, 'race,' adaptation to temperature, nutritional history and socioeconomic status. Some studies emphasize only one of these indicators and other studies consider combinations of indicators. To better understand the biocultural nature of human size and proportions a new study of the growth of Maya-American youngsters was undertaken in 1999 and 2000. One purpose of this research is to assess changes in body proportion between Maya growing up in the US and Maya growing up in Guatemala. Height and sitting height of 6-12-year-old boys and girls (n=360) were measured and the sitting height ratio [sitting height/height]x100, a measure of proportion, was calculated. These data are compared with a sample of Maya of the same ages living in Guatemala and measured in 1998 (n=1297). Maya-American children are currently 10.24 cm taller, on average, and have a significantly lower sitting height ratio, (i.e. relatively longer legs, averaging 7.02 cm longer) than the Guatemala Maya. Maya-American children have body proportions more like those of white children in the US than like Maya children in Guatemala. Improvements in the environment for growth, in terms of nutrition and health, seem to explain both the trends in greater stature and relatively longer legs for the Maya-Americans. These findings are applied to the problem of modern human origins as assessed from fossil skeletons. It has been proposed that heat adapted, relatively long-legged Homo sapiens from Africa replaced the cold adapted, relatively short-legged Homo neandertalensis of the Levant and Europe [J Hum Evol 32 (1997a) 423]. Skeletal samples of Maya adults from rural Guatemala have body proportions similar to adult Neandertals and to skeletal samples from Europe with evidence of nutritional and disease stress. Just as nutrition and health status explains the differences in the body proportions of living Maya children, these factors, along with adaptation to climate, may also explain much of the differences between the Neandertal and African hominid samples.

Migration of Maya refugees to the United States since the late 1970s affords the opportunity to study the consequences of life in a new environment on the growth of Maya children. The children of this study live in Indiantown, Florida, and Los Angeles, California. Maya children between 4 and 14 years old (n = 240) were measured for height, weight, fatness, and muscularity. Overall, compared with reference data for the United States, the Maya children are, on average, healthy and well nourished. They are taller and heavier and carry more fat and muscle mass than Maya children living in a village in Guatemala. However, they are shorter, on average, than children of black, Mexican-American, and white ethnicity living in Indiantown. Children of Maya immigrants born in the United States tend to be taller than immigrant children born in Guatemala or Mexico. Families that invest economic and social resources in their children have taller children. More economic successful families have taller children. Migration theory and political economy theory from the social sciences are combined with plasticity theory and life history theory (parental investment) from biology to interpret these data.

The rate of growth in height and the timing of adolescent growth events are analyzed for two samples of Guatemalan children. One sample includes Mayan school children, 33 boys and 12 girls between the ages of 5.00 to 17.99 years, living under poor conditions for growth and development. The second sample includes ladino children, 78 boys and 85 girls of the same age range, living under favorable conditions for growth. The Preece-Baines model I function is used to estimate mean values for rates and timing of childhood and adolescent growth events for the two groups. Significant statistical contrasts (t-tests) of these means show Mayan boys reach the age of "take-off" (TO; the onset of the adolescent growth spurt) 1.45 years later, achieve peak height velocity (PHV) 1.68 years later, and continue growing for about 2.0 years longer than do the ladino boys. Despite the Mayan boys' increased duration for growth they grow significantly more slowly than the ladinos. Mayan boys are 6.60 cm shorter than ladinos at the age of TO and are estimated to be 7.71 cm shorter than the ladinos at adulthood. Mayan girls reach the age of TO 0.93 years later than do the ladina girls, but the two groups do not differ in the age at PHV or the age at adulthood. The mean height of Mayan girls is significantly less than that of ladinas at the age of TO (6.5 cm), and this difference increases to an estimated 11.14 cm at adulthood. Possible causes of these ethnic and sex-related differences in amounts and rates of growth are discussed in relation to hypotheses about the genetic and environmental determinants of human development.

The measurement of within-population growth variability may be a sensitive indicator of environmental quality. Specifically, it is hypothesized that within-population variability will increase in adverse environments. To evaluate this hypothesis the variability in stature growth of three samples of Guatemala school children (5-10 years old) is assessed. These samples include high socioeconomic status (SES) ladinos (84 boys and 98 girls) and low SES ladinos (136 boys and 101 girls) living in Guatemala City and very low SES Mayan Indians (139 boys and 73 girls) living in a rural town near the city. SES is used as a proxy for environmental quality. The coefficient of variation (CV) for distance achieved at each age, or for the increment of growth from age to age, is used as the measure of variability. The three samples differ significantly for variability in stature growth, both for the distance and the increments of growth. Low SES urban ladinos have the largest variability. Very low SES Mayan children have coefficients of variation that are sometimes equal to, and sometimes either larger or smaller than, CVs for the high SES ladinos. The results show that degree of environmental adversity does not correlate uniformly with growth variability. Factors such as rates of infant and early childhood mortality and the greater heterogeneity of the low SES urban environment, compared with the high SES urban or low SES rural environments, may account for differences in the CV in these three samples.

Longitudinal data from a study of child development in Guatemala City were used to describe the influence of socioeconomic status and sex on physical and cognitive growth status. The correlation between the growth status variables was also analyzed. The sample included 144 Guatemalan children, 46 of low SES, 52 of middle SES, and 46 of high SES. The children were students in 5 urban primary schools. 3 physical variables, height, weight, and skeletal age, were measured annually from first to sixth grade. Two cognitive variables, general intelligence and reading ability, were measured in grades 1, 3, 4, or 5. Significant differences between SES groups existed for all variables. However, the differences in each grade were greater for the cognitive measures than for the physical measures. Compared with high SES children, middle SES boys and low SES boys and girls experienced significantly greater delayed growth in height than in weight or skeletal age. It is possible that these height delays may result in a permanent reduction in stature. The only consistently significant sex-related difference was for skeletal age; girls were more mature than boys in each grade. When SES was statistically controlled, there was no significant correlation between physical and cognitive growth status for girls and only a few moderate but statistically significant correlations for boys.

Monthly increments of height for a sample of 164 Guatemala City school children are analyzed for the presence of a seasonal pattern in rates of growth. It is found that pre and post adolescent children follow a seasonal pattern of growth but adolescent children do not. It is suggested that the results are due to an effect of seasonal changes in ultraviolet light availability and the synthesis of vitamin D3 as mediated by the level of maturation of each child.

Monthly increments of weight growth for a sample of 246 Guatemala City private school children are analyzed for the presence of a seasonal pattern in rates of growth. Neither a seasonal pattern nor any other periodic rhythm is found. It is observed that a significantly greater number of children aged 5.0 to 6.9 years experience their minimum annual growth rate during the dry season, with up to 60% of them losing or not gaining weight in any one month. Patterns of diet, exercise and disease cannot explain this trend. A possible association between minimum weight growth and maximum growth in height is discussed.

The relationship between rural to urban migration and child growth and family structure is reported in sample of 302 children from families of low socioeconomic status, living in Guatemala City. The sample was divided into three groups: 1) children of parents born outside the city, 2) children of parents born in the city, and 3) children with one migrant and one city-born parent. Children of migrants to the city were the smallest and significantly shorter than children of migrant city-born parents. Migrant parents also had the largest families; family size correlated negatively with growth in height. Growth in weight followed a pattern similar to height, but no significant differences associated with migration status were found between groups.