Ethnic and secular influences on the size and maturity of seven year old children living in Guatemala City.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 59:393-398(19821 Ethnic and Secular Influences on the Size and Maturity of Seven Year Old Children Living in Guatemala City BARRY BOGIN A N D ROBERT B. MACVEAN Wayne State Uniuersity, Detroit, Michigan 48202 (B.B.),and Universidad del Valle, Guatemala City, Guatemala (R.B.M.) Growth, Maturation, Ethnic influences, Secular KEY WORDS trends, Guatemala ABSTRACT Three groups of children, those of European parentage, those of Guatemalan parentage, and those of mixed European-Guatemalan parentage were measured for height, weight, and skeletal maturity. The children were born between 1945 and 1965,they were all of high socioeconomicstatus, and they all attended the same private school in Guatemala City. At 7 years, the boys of the European group were significantly taller than boys of the Guatemalan group. European and mixed European-Guatemalan girls were significantly taller than Guatemalan girls. These results are maturity independent. The influence of skeletal age was removed statistically by analysis of covariance. Girls of the mixed group were significantly heavier than girls of European and Guatemalan groups. Mixed group girls also had more significantly advanced skeletal ages than European girls. When the patterns of size and maturity status are analyzed by sex, there is evidence for a relatively greater environmental influence on the boys and a relatively greater genetic influence on the girls. Dividing the data into two birth year cohorts, 1945 to 1955, and 1956 to 1965, does not provide evidence for secular trends in growth or maturation. These results are similar to those from studies in developed nations that report an end to the secular trend for the “well off” population of those countries. Most of the many separate phenomena that contribute to the process of human growth and development are relatively easy to measure and quantify but difficult to explain. Two such phenomena are differences in mean size and rates of maturation between ethnic groups, and the secular trend for increases in both the amount and rate of growth and development. Eveleth and Tanner (1976) review growth studies of Europeans (London), AfroAmericans (Washington, D.C.), and Asians (Hong Kong). The Asian children were shorter than the European and Afro-Americans at almost every age between 1 and 18 years. Asian girls were found to reach menarche onehalf year earlier than Europeans and at about the same age as Afro-Americans. General socioeconomic conditions were similar and as close to optimum as possible in all groups. The authors consider these differences to have a genetic basis. However, since these populations are geographically and culturally remote from each other, environmental factors cannot be excluded. 0002-948318215904-0393$02.00 :r. 1982 ALAN R. LISS, INC. The secular trend for growth and development has also been responsible for differences in size and maturity of similar aged children between and within populations. Tanner (1962; 1968) and Roche (1979)describe and quantify the trends for earlier maturation and increased rate of growth. These trends have occurred in all the developed nations that have been studied and some of the developing countries (Roche, 1979). Most researchers find that the causes of the secular trend are primarily due to environmental improvements, e.g., socioeconomic conditions, sanitation, nutrition, and health care (Krogman, 1972; Tanner, 1968; Van Wieringen, 1978; Malina, 1979; Roche, 1979). But, there are some data indicating a possible genetic component to the trend as well (Hulse, 1958; Schreider, 1967). There are relatively few studies of secular trends in growth and maturation for children Received December 3. 1981; accepted July 7. 1982. Barry Bogin’s present address is University of Michigan, Dearborn, M I 48128. 394 B. BOGIN AND R.B. MACVEAN from developing nations. Basic data are needed to describe these trends, if present, and to compare them with the data from developed nations to understand better the causes and consequences of these trends. This paper presents data on the size and maturity of 7 year old children, born between 1945 and 1965, attending one private school in Guatemala. Children of three different ethnic backgrounds are represented. All of the children are of high socioeconomic class. The effects of ethnic background and the secular trend on the growth and maturity of these children are evaluated. An attempt is made to quantify each effect and to discuss possible hereditary and environmental influences on each. MATERIALS AND METHODS Data for this study were taken from the Longitudinal Study of Child Development conducted by the Universidad del Valle de Guatemala. The sample consists of children from the American School of Guatemala. Children attending this private school came from families of the highest socioeconomic levels of the country. The program at the American School assured each child regular medical attention, adequate nutrition, an intensive program of exercise and physical education, progressive academic education and yearly assessments of physical, and academic and cognitive status. In light of this background, we feel justified in describing this sample as representative of the most affluent children living in Guatemala. The data analyzed were the heights, weights, and skeletal ages of those study participants born between 1945 and 1965 (inclusive) assessed when each child was 7 years old (7.00 to 7.99 years). Height and weight measurement techniques and reliabilities were described by Bogin and MacVean (1978).Skeletal ages were assessed from hand-wrist radiographs. Exposures and assessments were made following the protocol of Gruelich and Pyle (1959). One technician read all the radiographs. Blind testretest readings of the same radiographs indicate a reliability coefficient of 0.89 for this technician. Seven years of age was chosen because it afforded the greatest number of children for each ethnic group and for the secular trend analysis. I t is an age a t which environmental influences on growth can be clearly demonstrated (Gold- stein, 1971), as well as population and ethnic differences (Eveleth and Tanner, 1976). The sample numbers 1208 children and was divided by sex and into three ethnic groups: American School Guatemalan (ASG), American School European (ASE), and American School Mixed (ASM). Children are classified ASE if both parents and all four grandparents were born in Europe or North America and have European (not Spanish) surnames. Children are classified as ASG if both parents and all four grandparents were born in Guatemala and have Spanish (not Mayan) surnames. Children classified as ASM are the offspring of marriages between an ASG and an ASE parent. The few individuals who did not meet any of these criteria were excluded from the sample. This genealogical classification is supported by data from the analysis of ABO blood group frequencies; ASG children have phenotypic frequencies significantly different from those of ASE children (Johnston et al., 1973). Ethnic identifications were made after all heights, weights, and skeletal ages were recorded. The identifications were based on information parents provided when completing school registration forms. RESULTS The data were first analyzed by a three-way analysis of variance to test for the main effects of year of birth, ethnicity, sex, and their interactions. In order to separately compare the effects of these variables on size and maturity, the heights of all children were adjusted to remove the influence of skeletal maturity by analysis of covariance. Table 1 is a summary of the results of the three-way ANOVA with height adjusted for skeletal age. Given in the table are the F ratios and beta values (betas may be interpreted as standardized partial regression coefficients). As can be seen there are some significant main effects but no interactive effects on each of the size and maturity variables. The data were further analyzed to describe the nature of the main effects. Table 2 shows the descriptive statistics for chronological age, height, weight, and skeletal age for boys of each ethnic group for all birth years combined. Corresponding statistics for the girls are given in Table 3. Heights were adjusted for skeletal age by covariance. Analysis of variance and post-hoc Scheffe tests were used to compare these means. There were no significant chronological age differences. For boys, there was one significant 395 ETHNIC AND SECULAR INFLUENCES ON SIZE AND MATURITY TABLE 1. Three way analysis of variance on height, weight, and skeletal age for the effects of year of birth, ethnicity and sex' Height' Weight F Beta F Beta Main effects df Year of birth 19 1.68* 0.14 1.74* 0.16 E thnicity 2 13.55** 0.13 2.50 0.06 Sex 1 66.00** 0.20 2.31 0.04 Interactions No simificant two-wav or three-wav interactions. Skeletal age F 1.23 4.27* 39.41** Beta 0.14 0.08 0.18 'n = 1208 'Heights were adjusted by covariance to statistically remove the effect of skeletal age. *p < 0.05: **p < 0.001. TABLE 2. Descriptive statistics for chronological age, height, ueight, and skeletal age for boys of the Guatemalan (ASG), European (ASE), and mixed Guatemalan-European (ASM)ethnic groups Chronological age (years) Height (cm) Weight (kg) Skeletal age (years) ASM ASE ASG n=412 n=171 ii sd X sd 7.51 124.16 25.36 0.28 4.80 3.95 7.47 125.59 25.75 0.29 4.80 4.74 6.93 1.09 6.84 1.19 n=102 ii sd 7.48 0.32 124.70 4.78 25.59 3.88 7.09 0.93 'Heights were adjusted by covariance to statistically remove the effect of skeletal age. 'ASE X > ASG X;p = 0.001. TABLE 3. Descriptive statistics for chronological age, height, weight, and skeletal age for girls of the Guatemalan (ASG), European (ASE),and mixed Guatemalan-EuroDean(ASMI ethnic grouus Chronological age (years) Height' Icm) Weight' (kg) Skeletal ageJ (wars) ASG ASE ASM n=276 n=158 n=92 X sd X sd X sd 7.47 121.71 24.83 0.29 4.80 4.25 7.47 123.32 25.20 0.29 4.79 5.07 7.51 123.37 26.45 0.31 4.81 5.69 7.30 0.84 7.22 0.91 7.50 0.98 'Heights were adjusted Iiy covariance to statistically remove the effectof skeletal age 'ASE X > ASCi X. p = 0.001: A S M X ASG X,p = 0 004. 'ASM X > ASG X: p = 0.005: ASM > ASE X: p = 0 05. 'ASM > ASK P = 0.02. x x. x difference for height: ASE boys were taller than ASG boys. No significant differences existed for weight or skeletal age. ASE and ASM girls were taller than ASG girls. ASM girls were significantly heavier than both ASE and ASG girls. ASM girls were more mature than ASE girls. The ASG girls were intermediate in value, but not significantly different from the other two groups. The data were then analyzed for secular trends within each ethnic group. Children were placed into two birth year cohorts, those born 1945-55 and those born 1956-65. Table 4 summarizes the analysis for trends in growth and 396 B. BOGIN AND R.B. MACVEAN TABLE 4. Descriptiue statistics for height, weight, and skeletal age for earlier born (1945-1955) and later born (1956-1965) cohorts o f children o f the Guatemalan (ASG), European (ASE), and mixed Guatemalan-European(ASM) ethnic groups ASG -~ Earlier born Later born n =.__ 142 n = 270 X sd X sd ~~~ ~ - ~ ~~ Boys Height (cm) Weight (kg) Skeletal age (years) Chronological age (years) Girls Height (em) Weight (kg) Skeletal age (years) Chronological age (years) ASE Earlier born Later born n = 71 n = 98 -~ Z __ sd X sd ~ ~ ~ ~ ASM Earlier born Later born n = 46 n = 56 X sd % sd ~~ ~ 123.08 5.18 124.02 5 0 8 125.76 5.66 124.22 5.84 123.76 4 68 125.43 4.66 25 38 3.99 25.35 3 94 26.22 4.73 25.44 4.77 25.20 3 52 25.90 4.15 7.06 1.18 6.67 1.19* 6.90 0.92 7 24 0 9 2 694 106 6 9 1 1.15 7.53 0.31 7.41 0 32 7.44 0.29 7.51 0.28 7.52 0.29 7 49 0 26 n = 87 n = 39 n = 53 n = 176 n = 71 n = 99 122.29 5.51 122.32 5.35 123.31 6.55 123.94 5.60 124.54 6.25 124.47 6.54 24.90 4.09 24.82 4.34 25.34 5.57 25.09 4.66 26.53 5.18 26.40 6.09 7.56 1.07 7.46 0.91 7.19 0.94 7.24 0.88 7.32 0.85 7.28 0.83 7.52 0.30 7.50 0.32 7.51 0.30 7.43 0.28 7.47 0.29 7.47 0.28 *Earlier born mean significantly greater t h a n later born mean. p < 0.05. maturation between the earlier born and later born cohorts. Means and standard deviations are given for all comparisons and significant differences between birth year cohorts were assessed by t-tests. For the girls, none of the ethnic groups showed significant differences. ASE boys showed a significant decrease in skeletal age. No other significant change was found for other variables in any of the ethnic groups. DISCUSSION The physical size and skeletal maturity of children of the same chronological age varies between and within populations. Differences in size and maturity a t a given age reflect hereditary factors, environmental conditions, and their interactive effects (Ashcroft and Lovell, 1964; Ashcroft et al., 1966; Garn and Rohmann, 1966; Hunt, 1966; Eveleth and Tanner, 1976; Johnston et al., 1976). The influence of heredity and environment are usually confounded in studies of child growth and development due to the nonexperimental nature of this research. However, some studies have attempted to statistically control for “nature vs. nurture.” Most of these studies found that during childhood growth and development were influenced relatively more by environmental factors, but during adolescence hereditary influences predominated (Gard and Rohman, 1966; Hunt, 1966; Habicht et al., 1974; Greulich, 1976; Johnston et al., 1976; Bogin, 1978; Tanner, 1978; Frisancho et al., 1980). Two exceptions to this general finding are studies by Ashcroft and Lovell (1964) and Ashcroft et al. (1966). They measured the heights and weights o f 4 to 17 year old children and youth of European, African, Afro-European, and Chinese background living in Kingston, Jamaica. All children were of uppermiddle to high socioeconomic status and attended private fee-paying schools. There were no significant differences between the European, African, and Afro-European groups. However, the Chinese sample was significantly shorter and lighter than the other three groups at almost every age. Our results are similar to those of Ashcroft and colleagues. Both our study and their’s show significant differences in growth between some ethnic groups of children reared in similar environments. These ethnic differences cannot be automatically ascribed to genetic factors. Neither the Jamaican study nor our Guatemalan study controlled for child rearing practices in the home, the length of residence of each family in the country, family size, or other cultural and behavioral variables that may have influenced growth. However, there is support for a genetic component to these ethnic differences when the results for boys and girls are compared. The mean heights and weights of the ASG, ASE, and ASM boys were more similar than the mean heights and weights of the girls. The variances for the boys were also relatively smaller than the variances for the girls. The data of Johnston e t al. (1976) also followed this pattern. They studied longitudinal growth patterns for children from the same population as that studied here. At 7 years ASG and ASE boys in their sample had identical mean heights, 123.5 cm (sd = 5.0 and 5.8, respective- ETHNIC AND SECULAR INFLUENCES ON SIZE AND MATURITY ly), and mean weights of 24.9 (3.7)and 25.6 (5.2) kg, respectively. The girls’ heights and weights were, ASG; 122.8 (5.6)cm and 25.2 (4.2)kg, versus ASE: 125.0 (6.2) cm and 26.1 (5.6) kg. Several other studies show similar findings. That is, when children of different ethnic groups live under similar environmental circumstances, the boys show similar amounts of growth and less variability, but the girls show less similarity and more variability between ethnic groups (Greulich, 1976; Bielicki and Charzewski, 1977). The interpretation of these observations given by Greulich is that the growth of boys is more “sensitive”to environmental influences. The growth of girls is less environmentally sensitive, rather it is influenced more by genetic factors. Our study supports this interpretation. There was only one significant difference for height between the three groups of boys. But, there were significant differences between the three groups of girls for all the growth variables. It is noteworthy that the ASM girls were consistently taller, heavier, and skeletally more mature than ASE and ASG girls. An additive genetic model cannot account for these results. I t would predict ASM children to be intermediate in size and maturity. Influences such as assortative mating, home environment, and others must be considered to explain the results. Unfortunately, we do not have data available for these influences. Finding significant ethnic differences between the ASG and ASE groups was, at first, surprising, since Johnston et al. (1976)did not find differences in growth between children from these same two groups. The discrepancy between our results and those of Johnston et al. may be due to sample size, 1208 vs. 58 respectively, or, more likely, to the crosssectional design of our study versus the longitudinal design of theirs. They were comparing patterns of accumulated growth, while we dealt with size at one age. Our results for the secular trend analysis are more easily interpreted. There has been no secular trend for the growth or maturation of upper socioeconomic children living in Guatemala, born between the years of 1945 to 1965. Our results parallel those from some developed countries, e.g., England, Japan, Norway, and the United States (Tanner, 1968; Dammon, 1968; Maresh, 1972) where children of the upper socioeconomic classes no longer experience secular growth changes. Presumably, these populations have realized 397 their maximum genetic potential for growth and maturation. On the other hand, in a study of low to middle socioeconomic status Guatemalans, Castefiada (1972) found a decrease in the age of menarche for three generations of women. Retrospective, self-reported data were used in this study. The mean age of menarche for school girls was 12.78 years, for their mothers 13.66 years and for their mothers’ mothers 14.18 years. There are also reports of positive secular trends for children living on the developing island nations of Jamaica (Ashcroft and Lovell, 1965), St. Vincent (Ashcroft and Antrobus, 1970),and Aruba (van Wering, 1981) during the past 30 years. These studies include children of all socioeconomic levels. All the authors explain their results in terms of the general socioeconomic, health, and nutritional improvement of the poor and middle class children during these years. This is the explanation for the secular trend favored by most researchers (Tanner, 1978; Malina, 1979; Roche, 1979). By negative evidence, our results also support the socioeconomic, health care, and nutrition explanation for the secular trend. All of our subjects were affluent, healthy, and well nourished. When these environmental factors do not inhibit growth, the child‘s hereditary potential for growth and development may be fully realized. Ethnic differences in growth and development may be observed between some groups, but secular trends are absent. LITERATURE CITED Ashcroft. MT, and Antrobus, ACK (1970) Heights and weights of school children in St. Vincent. J. Biosoc. Sci.. 2:3 17-328. Ashcroft, MT, Heneage, P. and Lovell, HG (1966) Heights and weights of Jamaican school children of various ethnic groups. Am. J. Phys. Anthropol.. 24:35-44. Ashcroft, MT, and Lovell, HG (1964) Heights and weights of Jamaican children of various racial orgins. Trop. Geogr. Med., 16:346-353. Ashcroft, MT, and Lovell, HG (1965)Changes in Jamaican schools between 1951 and 1964. West-Indian Med. J., 14:48-52. 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