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

Department of Mathematics, Physics, and Engineering, Tarleton State University, Box T-0010, Stephenville, TX 76402-0010, USA.
Human Biology (Impact Factor: 1.52). 07/2006; 78(3):295-305. DOI: 10.1353/hub.2006.0047
Source: PubMed

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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Differential investment in offspring by parental and progeny gender has been discussed and periodically analyzed for the past 80 years as an evolutionary adaptive strategy. Parental investment theory suggests that parents in poor condition have offspring in poor condition. Conversely, parents in good condition give rise to offspring in good condition. As formalized in the Trivers-Willard hypothesis (TWH), investment in daughters will be greater under poor conditions while sons receive greater parental investment under good conditions. Condition is ultimately equated to offspring reproductive fitness, with parents apparently using a strategy to maximize their genetic contribution to future generations. Analyses of sex ratio have been used to support parental investment theory and in many instances, though not all, results provide support for TWH. In the present investigation, economic strategies were analyzed in the context of offspring sex ratio and survival to reproductive age in a Zapotec-speaking community in the Valley of Oaxaca, southern Mexico. Growth status of children, adult stature, and agricultural resources were analyzed as proxies for parental and progeny condition in present and prior generations. Traditional marriage practice in Mesoamerican peasant communities is patrilocal postnuptial residence with investments largely favoring sons. The alternative, practiced by ∼25% of parents, is matrilocal postnuptial residence which is an investment favoring daughters. Results indicated that sex ratio of offspring survival to reproductive age was related to economic strategy and differed significantly between the patrilocal and matrilocal strategies. Variance in sex ratio was affected by condition of parents and significant differences in survival to reproductive age were strongly associated with economic strategy. While the results strongly support TWH, further studies in traditional anthropological populations are needed. Am J Phys Anthropol 143:501-511, 2010. © 2010 Wiley-Liss, Inc.
    American Journal of Physical Anthropology 12/2010; 143(4):501-511. DOI:10.1002/ajpa.21333 · 2.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The intensity of natural selection correlates with various bio-social variables which influence the genetic structure of a population. In this paper it has been sought to find out the influence of variable environmental setting and economic condition on selection intensity among the Mising tribal population of Assam, Northeast India. Detailed reproductive pattern of 309 post menopausal women is obtained and a comparison has been made between different environmental as well as economic backgrounds. The impact of secular change on selection intensity has been assessed. For this study I have proposed a modified formula of Johnston & Kensinger's (1971) index for selection intensity. Crow's index of selection intensity has also been used for comparative analyses. After considering standard statistical procedure, a clear disparity of selection intensity has been noticed in terms of varying socioeconomic condition as well as habitational background. It can be concluded from the study that environmental factors act more in terms of selection pressure on infants rather than the other post natal stages.
    Anthropologischer Anzeiger 07/2012; 69(3):273-87. DOI:10.1127/0003-5548/2012/0195 · 0.54 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study analysed the variations, both in space and time, of 10 body dimensions and 2 anthropometric indexes of 745 adult males belonging to 5 ethnic groups of historical Lybia (el-Haràbi, el-Baraghìts, Marabtìn, Oases inhabitants and Tuareg). The data were collected in the years 1928 and 1932 by Puccioni and Cipriani, two Italian anthropologists. The aim was to reconstruct the biological history of Libya at the time, and thus contribute to the ongoing debate on the evolution of the biological standard of living in developing Countries. The subjects were analysed by ethnicity and by 10-year age groups, after adjusting for age. The results of ANCOVA and Tukey's post-hoc test show that among and between groups there are statistical significant differences overall for armspan, height, head breadth, bizygomatic breadth, biiliac breadth/height and head breadth/head length indexes. By means of the cluster analysis, the el-Haràbi, el-Baraghìts and Marabtìn groups cluster together, whereas the Tuareg and Oases inhabitants cluster separately one from the other and both from the other three ethnic groups. Within-group variations are not very marked in all ethnicities. In general, there is the tendency, not statistically significant, to the reduction and/or stasis of body dimensions from the older to the younger, and the differences are greater among the older than the younger age classes. In conclusion, it can be argued that these groups, all different culturally and geographically, were following the same tendency of stasis of the secular trend of the body dimensions considered in this study, and such stasis persisted since, at least, the last twenty years of the 19th century, when the older were born.
    Journal of anthropological sciences 07/2011; 89:127-38. DOI:10.4436/jass.89009 · 1.70 Impact Factor