Evolutionary Adaptation to High Altitude: A View From In Utero

Department of Anthropology, University of Colorado Denver, Denver, Colorado, USA.
American Journal of Human Biology (Impact Factor: 1.7). 09/2009; 21(5):614-22. DOI: 10.1002/ajhb.20900
Source: PubMed


A primary focus within biological anthropology has been to elucidate the processes of evolutionary adaptation. Frisancho helped to move anthropology towards more mechanistic explanations of human adaptation by drawing attention to the importance of the functional relevance of human variation. Using the natural laboratory of high altitude, he and others asked whether the unique physiology of indigenous high-altitude residents was the result of acclimatization, developmental plasticity, and/or genetic adaptation in response to the high-altitude environment. We approach the question of human adaptation to high altitude from a somewhat unique vantage point; namely, by examining physiological characteristics-pregnancy and pregnancy outcome-which are closely associated with reproductive fitness. Here we review the potent example of high-altitude native population's resistance to hypoxia-associated reductions in birth weight, which is often associated with higher infant morbidity and mortality at high altitude. With the exception of two recent publications, these comparative birth weight studies have utilized surnames, self-identification, and/or linguistic characteristics to assess ancestry, and none have linked 'advantageous' phenotypes to specific genetic variations. Recent advancements in genetic and statistical tools have enabled us to assess individual ancestry with higher resolution, identify the genetic basis of complex phenotypes and to infer the effect of natural selection on specific gene regions. Using these technologies our studies are now directed to determine the genetic variations that underlie the mechanisms by which high-altitude ancestry protects fetal growth and, in turn, to further our understanding of evolutionary processes involved in human adaptation to high altitude.

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Available from: Colleen Glyde Julian
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    • "However, in a substantial number of pregnant hypertensive women, the pregnancy outcome is similar to normotensive women. It has been pointed out that this aspect reflects foetal circulatory independence from the mother that enables the induction of adaptive responses to cope with the maternal haemodynamic compromise [21-24]. "
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    ABSTRACT: The foetal aortic Doppler frequency spectrum is influenced by cardiac output and contractility of the foetal heart as well as vascular compliance, blood viscosity and impedance of the arterial vascular system. The present study aimed at comparing Doppler flow pulsatility (PI) and resistance (RI) indexes of foetal proximal descending aorta (AoF) in the first, second and third trimesters of pregnancy, in low risk women and in those with chronic arterial hypertension, who had normal pregnancy outcomes. A longitudinal and prospective study was carried out in 101 singleton pregnancies (71 low-risk pregnancies and 30 with essential hypertension). Multivariate regression had to be considered due to the experiment's nature: two different indexes were read on the same set of individuals, once at each trimester of the pregnancy [1st (11-14 weeks), 2nd (19-22 weeks) and 3rd (28-32 weeks) trimesters]. The response variable was denoted as index d, in a subject with hypertensive status h (hypertensive or normotensive), at continuous time t. In both groups, AoF-PI and AoF-RI showed a small, but significant increase from the first to the second (1.850 +/- 0.339 vs 2.110 +/- 0.242 for PI, and 0.829 +/- 0.068 vs 0.857 +/- 0.038 for RI; p < 0.001) and the first to the third (1.850 +/- 0.339 vs 2.163 +/- 0.282 for PI, and 0.829 +/- 0.068 vs 0.864 +/- 0.037 for RI; p < 0.001) trimesters of pregnancy. The global model showed that while AoF-RI trends were converging as time progressed, the AoF-PI values exhibited a divergent trend (p < 0.05). Chronic stable hypertension in pregnancies with normal outcome, evidences an upward regular trend of foetal descending aorta pulsatility index that is similar to the normotensive condition.
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    • "Another characteristic of the Tibetan population is a relative protection against the occurrence of intrauterine growth restriction (IUGR), which is associated with low birth weight at high altitude. It is well recognized that reproductive success is more difficult at high than low altitude, especially among nonnatives (43). Birth weight progressively reduces with increasing altitude across populations (41, 56, 97). "
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    ABSTRACT: The Tibetan Plateau is one of the highest regions on Earth. Tibetan highlanders are adapted to life and reproduction in a hypoxic environment and possess a suite of distinctive physiological traits. Recent studies have identified genomic loci that have undergone natural selection in Tibetans. Two of these loci - EGLN1 and EPAS1 - encode major components of the hypoxia-inducible factor (HIF) transcriptional system, which has a central role in oxygen sensing and coordinating an organism's response to hypoxia, as evidenced by studies in humans and mice. An association between genetic variants within these genes and hemoglobin concentration in Tibetans at high altitude was demonstrated in some of the studies (8, 78, 94). Nevertheless, the functional variants within these genes and the underlying mechanisms of action are still not known. Furthermore, there are a number of other possible phenotypic traits, besides hemoglobin concentration, upon which natural selection may have acted. Integration of studies at the genomic level with functional molecular studies and studies in systems physiology has the potential to provide further understanding of human evolution in response to high-altitude hypoxia. The Tibetan paradigm provides further insight on the role of the HIF system in humans in relation to oxygen homeostasis.
    Full-text · Article · Nov 2013 · Journal of Applied Physiology
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    • "Studies show that the anthropological characteristics of these populations are related to the adaptation process to extreme environments. Specifically, low birth weight are reported, as well as slow and prolonged growth which translates to lower height at an adult age (Lomaglio et al., 2005; Espinoza-Navarro et al., 2009; Julian et al., 2009). "

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