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  1. Fix AG
    Am. J. Hum. Biol., 2004 Jul-Aug;16(4):387-94.
    PMID: 15214057
    Migration among local populations classically has been seen as the principal process retarding genetic microdifferentiation. However, as Sewall Wright pointed out long ago, migration may also act as a random differentiating force. In fact, when migrants comprise a biological kin group, migration may be considered a component of genetic drift. The causes of kin-structured migration (KSM) lie in the common, if not universal, tendency for kin to associate and cooperate. However, similar to genetic drift, KSM has its greatest effect in smaller populations and is most apparent in low-density fission-fusion societies such as the Yanomamo of South America and the Semai of Malaysia, and less salient in higher density, low-mobility populations such as those of the New Guinea Highlands. The evolutionary consequences of KSM begin with increased genetic variation among populations. Such intergroup variation provides a basis for group selection. The origin of larger-scale geographic differentiation can arise from kin-structured migrant groups colonizing new regions. Waves of colonizing kin-structured founder groups may produce gene frequency clines, mimicking demic diffusion and natural selection. Finally, because kin structuring reduces the effective size of a population, it may be speculated that the extremely small effective size inferred for ancestral populations of Homo sapiens may be an artifact of kin-structured demographically larger populations.
  2. Nepomnaschy PA, Welch K, McConnell D, Strassmann BI, England BG
    Am. J. Hum. Biol., 2004 Sep-Oct;16(5):523-32.
    PMID: 15368600 DOI: 10.1002/ajhb.20057
    We report here on a longitudinal study of stress and women's reproduction in a small Kaqchikel Mayan community in rural Guatemala. Current understanding of the effects of stress on the reproductive axis in women is mostly derived from clinical studies of individual stressors. Little is known, however, about the cumulative effects of "real life" stress. Cortisol increases in response to a broad variety of individual stressors (Tilbrook et al., 2002). In this article, we evaluate the association between daily fluctuations in women's urinary cortisol and reproductive hormones: estrone conjugates (E(1)C), pregnandiol glucuronide (PdG), luteinizing hormone (LH), and follicle stimulating hormone (FSH). To assess the association between daily changes in cortisol levels and changes in the profiles of the reproductive hormones, we used a random coefficients model based on polynomial regression. The sample includes 92 menstrual cycles provided by 24 participants over a year-long prospective study. Increases in urinary cortisol levels were associated with significant increases in gonadotrophin and progestin levels during the follicular phase. Also, in a time window between days 4 and 10 after ovulation, increased cortisol levels were associated with significantly lower progestin levels. These results are significant because untimely increases in gonadotrophins and low midluteal progesterone levels have previously been reported to impinge on the ovulatory and luteinization processes and to reduce the chances of successful implantation (Ferin, 1999; Baird et al., 1999). Future research should consider the possibility that stress may affect fecundability and implantation without necessarily causing amenorrhoea or oligomenorrhoea.
  3. Henry CJ, Webster-Gandy JD, Koon PB, Ismail MN
    Am. J. Hum. Biol., 2005 Nov-Dec;17(6):818-20.
    PMID: 16254909
    This cross-sectional study of age matched (10-11 years), pre-menarcheal girls in England and Malaysia investigated the effect of ethnicity on resting metabolic rate (RMR). The children were recruited from schools in Oxford, England, and Kuala Lumpur, Malaysia, and all measurements were conducted in the schools. The Malaysian girls were shorter (143.7 +/- 6.5 cm and 140.1 +/- 5.3 cm (mean +/- SD) for the English and Malaysian girls respectively) and lighter (32.5 +/- 5.3 kg compared with 38.0 +/- 8.7 kg for the English girls) with a smaller fat mass and fat free mass (FFM) than the English girls. Energy expenditure was lower in the Malaysian girls (4555 +/- 531 kJ/day compared with 5178 +/- 688 kJ/day for the English girls). Although a difference in RMR was observed between the two groups, when corrected for body composition the difference was no longer significant. No effect of ethnicity on the relationship of FFM and RMR was shown when the data were analyzed using analysis of covariance.
  4. Duncan MT, Husain R, Chen HM, Horvath SM
    Am. J. Hum. Biol., 1995;7(3):329-337.
    PMID: 28557027 DOI: 10.1002/ajhb.1310070309
    The interaction of race and climatic adaptation on patterns of cardiovascular reactivity among young adult males was examined. Malay and Chinese subjects living in a tropical climate in the Orient and Caucasians living in a sub-tropical climate in North America were investigated. The cold pressor test with hand immersion in cold water was used as the stressor. Systolic and diastolic blood pressures, cardiac frequency, cardiac output, and stroke volume were measured. The results provided limited evidence for absence of differences in cardiac reactivity among racial groups and for greater vascular reactivity in the Caucasians. Cold immersion also elicited differential responses which could be partially attributed to differences in acclimatizations status. © 1995 Wiley-Liss, Inc.
  5. Fix AG
    Am. J. Hum. Biol., 1989;1(4):463-469.
    PMID: 28514113 DOI: 10.1002/ajhb.1310010409
    The fertility and parameters of population growth of the Semai Senoi of Malaysia are studied by using a two-census method based on nonstable population theory. Semai fertility is shown to be moderately high; female completed fertility is 7.42 children and the crude birth rate is greater than 0.050. Previous estimates of Semai mortality rates are also moderately high but are insufficient to balance birth; thus, the overall rate of growth is presently nearly 2%. Compared with an earlier description of the pre-1969 Semai population, fertility has increased markedly leading to a nearly threefold increase in the annual growth rate.
  6. Fix AG
    Am. J. Hum. Biol., 1989;1(4):471-477.
    PMID: 28514106 DOI: 10.1002/ajhb.1310010410
    The mortality pattern of a subpopulation of Semai Senoi of Malaysia is studied by using a two-census method. The method yields abridged life tables for both sexes as well as an estimate of the birth rate. The life tables show that Semai mortality is reduced compared to estimates based on stable population methods for the population prior to 1969. Increased health care availability seems to account for this lower mortality.
  7. Huber S, Fieder M
    Am. J. Hum. Biol., 2018 01;30(1).
    PMID: 28960565 DOI: 10.1002/ajhb.23064
    OBJECTIVES: Homogamy, mating based on similarity, has been demonstrated for a great variety of traits such as age, education, religion, and physical and psychological traits. Recently, pro-fertile effects of religious as well as educational homogamy have been reported. We investigate whether ethnic homogamy also has a pro-fertile effect and whether ethnic and religious homogamy interact in their putative effects on reproduction (in terms of average number of offspring).

    METHODS: We analyzed the association between ethnic as well as religious homogamy and woman's average number of offspring based on census data from ten countries provided by IPUMS international, encompassing a total of 1,485,433 married women aged 46-60 years (who have thus completed or almost completed reproduction) and their spouses.

    RESULTS: We find a clear pro-fertile but nonadditive effect of both ethnic and religious homogamy, which is most pronounced in the case of double homogamy. Our results further indicate that homogamy for one trait may compensate for heterogamy of the other, albeit countries differ regarding which trait compensates for the other.

    CONCLUSIONS: We suggest that the interaction between ethnic homogamy, religious homogamy, and reproduction provides an interesting example for gene-culture co-evolution.

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