Opportunity for Natural Selection and Gene Flow in an Isolated Zapotec-Speaking Community in Southern Mexico in the Throes of a Secular Increase in Size

Abstract

Our object in this paper is to analyze the opportunity for natural selection and gene flow in an isolated Zapotec-speaking community in the valley of Oaxaca, southern Mexico, that is undergoing a secular increase in body size. Surveys were conducted in the community in 1968, 1978, and 2000, including anthropometric and census data. No secular change was found in the growth status of schoolchildren and adult height between 1968 and 1978; subsequently, major secular gains in height occurred among children and adolescents between 1978 and 2000. The 1978 household data were used to compute gene flow (3.3%) and opportunity for selection intensity (I = 1.312). Migration and other demographic information was obtained from household census data for 1978 and 2000, and mortality information was extracted from community records and archives. These data were used to compute gene flow and opportunity for natural selection. Gene flow increased from 3.3% to 4.7% and intensity of natural selection decreased from 1.312 to 0.272 from 1978 to 2000. Variance in fertility increased slightly over time (12.25 to 13.69). Opportunity for selection was dominant during the prereproductive period in 1978, but approached 0 for the mortality component in 2000, resulting in a marked decrease in the mortality component (Im) of selection (0.626 and 0.019, respectively) and total opportunity for selection (I = 1.312 and 0.272, respectively). Secular increase in height and markedly decreased opportunity for natural selection (1) were associated with better health and nutritional conditions. Genotype-environment interaction and environmental influences are apparently the predominant causes of the secular trend. If natural selection plays a role in causing the secular trend, it is a small one.

Overweight and obesity in a rural amerindian population in Oaxaca, Southern Mexico, 1968–2000

“…Estimated inbreeding was moderately high (0.01) and gene flow was very low (*3.3%), while natural selection was slightly more intense (10%) than would be predicted given population and subsistence characteristics Malina, 1989, 2005). Natural selection intensity was influenced largely through prereproductive mortality (Little et al, 2006b).…”

Epidemiologic transition in an isolated indigenous community in the Valley of Oaxaca, Mexico

“…1). The community was economically isolated until quite recently and is still genetically isolated Little et al, 2006). National census figures indicated a population of 1,423 in 1970(Secretaria de Industria y Comercio, 1971), 1,823 in 1980, 1,954 in 1990 in 2000 (Instituto Nacional de Estadística, Geografía e Informá tica [INEGI], 1984[INEGI], , 1991[INEGI], , 2002.…”

“…It is estimated that the community has been relatively isolated genetically since 900 A.D. Little et al, 2006). Estimated inbreeding was moderately high (0.01), and gene flow was very low (3.3%); natural selection was slightly more intense (10%) than would be predicted given population and subsistence characteristics Malina, 1989, 2005).…”

Marriage patterns in a Mesoamerican peasant community are biologically adaptive

“…Among 336 schoolchildren 6–15 years surveyed in 1968, 132 were no longer resident in the community in Fall 1978 (Malina et al,1982b); thus, about 60% of school youth resident in the community in 1968 were present in 1978, suggesting about 40% out‐migration as school‐aged mortality was ∼1–2%. Emigrants were ≥18 years and usually from poorer households (Little et al,2006), but did not differ in height at school age compared to those who remained in the community (Malina et al,1982b). “Push” factors for migration at the time of study were lack of economic and employment opportunities in the community; “pull” factors were economic and employment opportunities in major urban centers, primarily Mexico City.…”

“…Emigration did not, however, impact acculturation. In 1978 more than 75% of community inhabitants spoke only Zapotec (Malina et al,2008), >95% of heads of household were full‐time farmers (Malina et al,1985), and an estimated 3% of the population's genes were from outside the community (Little and Malina,1989; Little et al,2006,2008).…”