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Sexual assault evidence often contains sperm cells, which are typically separated from nonsperm cells using manual differential lysis procedures. The goal of this study was to evaluate the automated QIAGEN QIAcube for this purpose and to compare it to manual QIAGEN and manual organic differential methods using DNA yields and STR profile data for assessment. DNA yields were determined by qPCR, followed by multiplex STR amplification, CE analysis, and mixture interpretation. The automated method was capable of effective cell separation, producing DNA yields sufficient for STR amplification. Further, sperm fraction human:male DNA ratios from the QIAcube samples were consistently closer to the desired 1:1 and STR profiles were less likely to result in mixtures, with 6-8× fewer female alleles detected (median 1.5 alleles). Ultimately, using the QIAcube for automated differential processing of semen-containing mixtures reduces the need for downstream mixture interpretation and improves STR profile quality with substantially less hands-on time., (© 2019 The Author(s). Published by Taylor & Francis Group on behalf of the Academy of Forensic Science.)

Plastic debris has been documented in many marine ecosystems, including remote coastlines, the water column, the deep sea, and subtropical gyres. The North Pacific Subtropical Gyre (NPSG), colloquially called the "Great Pacific Garbage Patch," has been an area of particular scientific and public concern. However, quantitative assessments of the extent and variability of plastic in the NPSG have been limited. Here, we quantify the distribution, abundance, and size of plastic in a subset of the eastern Pacific (approximately 20-40°N, 120-155°W) over multiple spatial scales. Samples were collected in Summer 2009 using surface and subsurface plankton net tows and quantitative visual observations, and Fall 2010 using surface net tows only. We documented widespread, though spatially variable, plastic pollution in this portion of the NPSG and adjacent waters. The overall median microplastic numerical concentration in Summer 2009 was 0.448 particles m(-2) and in Fall 2010 was 0.021 particles m(-2), but plastic concentrations were highly variable over the submesoscale (10 s of km). Size-frequency spectra were skewed towards small particles, with the most abundant particles having a cross-sectional area of approximately 0.01 cm(2). Most microplastic was found on the sea surface, with the highest densities detected in low-wind conditions. The numerical majority of objects were small particles collected with nets, but the majority of debris surface area was found in large objects assessed visually. Our ability to detect high-plastic areas varied with methodology, as stations with substantial microplastic did not necessarily also contain large visually observable objects. A power analysis of our data suggests that high variability of surface microplastic will make future changes in abundance difficult to detect without substantial sampling effort. Our findings suggest that assessment and monitoring of oceanic plastic debris must account for high spatial variability, particularly in regards to the evaluation of initiatives designed to reduce marine debris.

Substantial quantities of small plastic particles, termed "microplastic," have been found in many areas of the world ocean, and have accumulated in particularly high densities on the surface of the subtropical gyres. While plastic debris has been documented on the surface of the North Pacific Subtropical Gyre (NPSG) since the early 1970s, the ecological implications remain poorly understood. Organisms associated with floating objects, termed the "rafting assemblage," are an important component of the NPSG ecosystem. These objects are often dominated by abundant and fast-growing gooseneck barnacles (Lepas spp.), which predate on plankton and larval fishes at the sea surface. To assess the potential effects of microplastic on the rafting community, we examined the gastrointestinal tracts of 385 barnacles collected from the NPSG for evidence of plastic ingestion. We found that 33.5% of the barnacles had plastic particles present in their gastrointestinal tract, ranging from one plastic particle to a maximum of 30 particles. Particle ingestion was positively correlated to capitulum length, and no blockage of the stomach or intestines was observed. The majority of ingested plastic was polyethylene, with polypropylene and polystyrene also present. Our results suggest that barnacle ingestion of microplastic is relatively common, with unknown trophic impacts on the rafting community and the NPSG ecosystem.

Online social media tools can be some of the most rewarding and informative resources for scientists-IF you know how to use them., Competing Interests: The authors have declared that no competing interests exist.

Plastic pollution in the form of small particles (diameter less than 5 mm)--termed 'microplastic'--has been observed in many parts of the world ocean. They are known to interact with biota on the individual level, e.g. through ingestion, but their population-level impacts are largely unknown. One potential mechanism for microplastic-induced alteration of pelagic ecosystems is through the introduction of hard-substrate habitat to ecosystems where it is naturally rare. Here, we show that microplastic concentrations in the North Pacific Subtropical Gyre (NPSG) have increased by two orders of magnitude in the past four decades, and that this increase has released the pelagic insect Halobates sericeus from substrate limitation for oviposition. High concentrations of microplastic in the NPSG resulted in a positive correlation between H. sericeus and microplastic, and an overall increase in H. sericeus egg densities. Predation on H. sericeus eggs and recent hatchlings may facilitate the transfer of energy between pelagic- and substrate-associated assemblages. The dynamics of hard-substrate-associated organisms may be important to understanding the ecological impacts of oceanic microplastic pollution.

This paper focuses on assistance that externally-resident daughters provide for their aging parents in rural Tibet, China, to challenge the notion that rapid modernization invariably threatens family-based care systems for the elderly. The authors discuss social and economic changes associated with modernization that have created new opportunities for parents to send daughters out of their natal households in ways that can benefit them in old age. By investing in a daughter's education so she can secure salaried employment, or by helping a daughter establish a small business so she can earn an independent livelihood, the authors demonstrate how some externally-resident daughters represent a novel form of social capital that parents can draw on for social support. Daughters with income and freedom from extended family obligations are now providing elderly parents with (1) leverage against co-resident children who do not treat them well, (2) temporary places of refuge from ill-treatment at home, (3) caretaking services and financial support when they require hospitalization, and (4) financial resources independent of their household which they can use to pursue age-appropriate activities like pilgrimage. The authors conclude that this new form of social capital vested in externally-resident daughters is having a positive impact on the lives of the elderly in rural Tibet.

Here we test the hypothesis that high-altitude native resident Tibetan women with genotypes for high oxygen saturation of hemoglobin, and thus less physiological hypoxic stress, have higher Darwinian fitness than women with low oxygen saturation genotypes. Oxygen saturation and genealogical data were collected from residents of 905 households in 14 villages at altitudes of 3,800-4,200 m in the Tibet Autonomous Region along with fertility histories from 1,749 women. Segregation analysis confirmed a major gene locus with an autosomal dominant mode of inheritance for high oxygen saturation levels, associated with a 10% higher mean. Oxygen saturation genotypic probability estimators were then used to calculate the effect of the inferred oxygen saturation locus on measures of fertility, in a subsample of 691 women (20-59 years of age and still married to their first husbands, those with the highest exposure to the risk of pregnancy). The genotypic probability estimators were not significantly associated with the number of pregnancies or live births. The high oxygen saturation genotypic mean offspring mortality was significantly lower, at 0.48 deaths compared with 2.53 for the low oxygen saturation homozygote, because of lower infant mortality. Tibetan women with a high likelihood of possessing one to two alleles for high oxygen saturation had more surviving children. These findings suggest that high-altitude hypoxia is acting as an agent of natural selection on the locus for oxygen saturation of hemoglobin by the mechanism of higher infant survival of Tibetan women with high oxygen saturation genotypes.

Elevated hemoglobin concentrations have been reported for high-altitude sojourners and Andean high-altitude natives since early in the 20th century. Thus, reports that have appeared since the 1970s describing relatively low hemoglobin concentration among Tibetan high-altitude natives were unexpected. These suggested a hypothesis of population differences in hematological response to high-altitude hypoxia. A case of quantitatively different responses to one environmental stress would offer an opportunity to study the broad evolutionary question of the origin of adaptations. However, many factors may confound population comparisons. The present study was designed to test the null hypothesis of no difference in mean hemoglobin concentration of Tibetan and Aymara native residents at 3,800-4,065 meters by using healthy samples that were screened for iron deficiency, abnormal hemoglobins, and thalassemias, recruited and assessed using the same techniques. The hypothesis was rejected, because Tibetan males had a significantly lower mean hemoglobin concentration of 15.6 gm/dl compared with 19.2 gm/dl for Aymara males, and Tibetan females had a mean hemoglobin concentration of 14.2 gm/dl compared with 17.8 gm/dl for Aymara females. The Tibetan hemoglobin distribution closely resembled that from a comparable, sea-level sample from the United States, whereas the Aymara distribution was shifted toward 3-4 gm/dl higher values. Genetic factors accounted for a very high proportion of the phenotypic variance in hemoglobin concentration in both samples (0.86 in the Tibetan sample and 0.87 in the Aymara sample). The presence of significant genetic variance means that there is the potential for natural selection and genetic adaptation of hemoglobin concentration in Tibetan and Aymara high-altitude populations.

Newcomers acclimatizing to high altitude and adult male Tibetan high altitude natives have increased ventilation relative to sea level natives at sea level. However, Andean and Rocky Mountain high altitude natives have an intermediate level of ventilation lower than that of newcomers and Tibetan high altitude natives although generally higher than that of sea level natives at sea level. Because the reason for the relative hypoventilation of some high altitude native populations was unknown, a study was designed to describe ventilation from adolescence through old age in samples of Tibetan and Andean high altitude natives and to estimate the relative genetic and environmental influences. This paper compares resting ventilation and hypoxic ventilatory response (HVR) of 320 Tibetans 9-82 years of age and 542 Bolivian Aymara 13-94 years of age, native residents at 3,800-4,065 m. Tibetan resting ventilation was roughly 1.5 times higher and Tibetan HVR was roughly double that of Aymara. Greater duration of hypoxia (older age) was not an important source of variation in resting ventilation or HVR in either sample. That is, contrary to previous studies, neither sample acquired hypoventilation in the age ranges under study. Within populations, greater severity of hypoxia (lower percent of oxygen saturation of arterial hemoglobin) was associated with slightly higher resting ventilation among Tibetans and lower resting ventilation and HVR among Aymara women, although the associations accounted for just 2-7% of the variation. Between populations, the Tibetan sample was more hypoxic and had higher resting ventilation and HVR. Other systematic environmental contrasts did not appear to elevate Tibetan or depress Aymara ventilation. There was more intrapopulation genetic variation in these traits in the Tibetan than the Aymara sample. Thirty-five percent of the Tibetan, but none of the Aymara, resting ventilation variance was due to genetic differences among individuals. Thirty-one percent of the Tibetan HVR, but just 21% of the Aymara, HVR variance was due to genetic differences among individuals. Thus there is greater potential for evolutionary change in these traits in the Tibetans. Presently, there are two different ventilation phenotypes among high altitude natives as compared with sea level populations at sea level: lifelong sustained high resting ventilation and a moderate HVR among Tibetans in contrast with a slightly elevated resting ventilation and a low HVR among Aymara.

This study was designed to test the hypothesis that genetic differences inferred from biological kinship relationships among individuals contribute to individual variation in percentage of oxygen saturation of arterial hemoglobin (SaO2) in a high-altitude native population. SaO2 data were obtained by pulse oximetry from 354 nonpregnant, healthy Tibetan residents of Pen-Dri, two rural agropastoral villages at 3800-4065 m altitude in Lhasa Municipal District, Tibet Autonomous Region, China. Statistical analyses of these data from 46 pedigrees tested the hypothesis of a significant genetic contribution to SaO2 variation. The average SaO2 was 89.4 +/- 0.2%, with a range of 76-97%. Additive genetic effects account for 44% of the interindividual phenotypic variation in SaO2 in the sample. Complex segregation analysis and variance decomposition analysis determined that 21% of the total phenotypic variation could be explained by a major gene influencing SaO2. Homozygotes for the low-SaO2 allele have a mean SaO2 of 83.6%, whereas heterozygotes and homozygotes for the high-SaO2 allele have means of 87.6% and 88.3%, respectively. This confirms findings in another Tibetan sample and extends the known geographic distribution of the major gene. These results suggest the hypothesis that individuals with the dominant allele for higher SaO2 have a selective advantage in their high-altitude hypoxic environment.

The results of 51 overnight measurements of basal metabolic rate (BMR) in a sample of pastoral nomads resident permanently in Phala, Tibet Autonomous Region, China, are reported. Past studies demonstrated a culturally driven seasonality of diet, with very low summer and very high winter caloric intake. The study was designed to test the hypothesis that the ability of Phala nomads to subsist on low caloric intake for several summer months without signs of malnutrition is explained by lower summer BMR. However, BMR measurements of 40 nomads 13-69 years of age during the summer and remeasurement of 11 nomads during the winter of 1993 provide no evidence for low summer BMR to compensate for the low summer caloric intake. BMR in both seasons is within the normal range predicted by international equations. The BMR of males does not differ from that of females, and the BMR of females averages 7% higher than predicted. Anthropometric evidence reveals that the Phala nomads accumulate body fat during the winter. It is inferred that this may buffer the summer period of low intake. The pattern of subcutaneous fat accumulation in winter, moreover, may afford slight improvement in physiological cold insulation during the severe winters as a consequence of depositing winter fat on the trunk rather than on the periphery. Thus, the dietary seasonality in Phala is a stress that elicits fluctuation in fat energy stores but not BMR. © 1996 Wiley-Liss, Inc., (Copyright © 1996 Wiley-Liss, Inc.)

This report employs a statistical genetic approach to analyze quantitative oxygen transport variables in a high-altitude (4,850-5,450 m) native Tibetan population and demonstrates the presence of a major gene influencing % O2 saturation of arterial hemoglobin. This result suggests the hypothesis that individuals with the dominant allele for higher % O2 saturation have a selective advantage at high altitude. Studies of the biologically distinctive Himalayan and Andean populations have greatly influenced thinking about ongoing human evolution and adaptation; this is the first statistical evidence for a major gene enhancing oxygen transport in a high-altitude native population.

This paper examines the net income of a sample of 100 elderly living in two villages in Zhejiang Province. A natural experimental study design was employed to examine village differences in prosperity while controlling for other linguistic and cultural/regional factors that might influence the economic status of the elderly. The paper examines the different sources of income for the sample elderly and assesses their general economic status. It found that while most of the income of the elderly derived from their own farming and sideline work, children also assisted elderly parents and provided a safety-net for them as their physical capacity waned. However, having many sons did not improve the economic status of the elderly and the majority of elderly now preferred only one son.

This paper presents information on body size, body composition, and fat patterning in a sample of 750 pastoral nomads aged 5 to 84 years, native residents of Moost district, Mongolia and evaluates the results from the perspective of morphological adaptation to a cold climate. Mongolian nomad men and children have average BMIs close to the U.S. 25th percentile while women have average BMIs close to the U.S. reference median. The prevalence of excess fatness assessed by the Arm Fat Index rises from 5 to 15% during childhood to 65% or more in each adult age-sex group except women 70+ years. The pattern of fat deposition is markedly central (abdominal) among women and children while it is normally so among men: women and children have a very high ratio of waist-to-hip circumference and children have a moderately high ratio of subscapular-to-triceps skinfold compared with other populations. A body composition favoring centrally deposited fat may be adaptive to a cold stressed population because it would aid in heat production (abdominal fat is thermogenic) and heat conservation (more spherical body size and better insulation) in the age-sex groups that are usually at a thermal disadvantage because of small body size and/or low basal metabolic rate relative to men. © 1992 Wiley-Liss, Inc., (Copyright © 1992 Wiley-Liss, Inc., A Wiley Company.)

This paper reports on the household composition of a sample of elderly residing in two villages in Zhejiang Province, China, one that is prospering under the post 1978 economic reforms and another that is not. It reveals that while a large proportion of the elderly in both the study villages are part of single generation households, the two villages differ with respect to the composition of the single generation household category. In the prosperous village, 50% of the elderly are living alone or with a spouse and 6% are living "by turns" (rotating between son's residences). In the less prosperous village, 26% are living alone or with a spouse while 22% participate in "by turns" arrangements. The paper suggests that a failure to separate analytically the "by turns" arrangements obscures the extent to which China's rural elderly now live in economic units separate from their offspring and masks important aspects of the differential impact of the new economic reforms on the household situation of the elderly in different villages.

To investigate why family planning (FP) services in the Kathmandu Valley of Nepal are underused, a study was initiated under the auspices of the Nepal Family Planning/Maternal--Child Health Project. The study was intended to provide a user perspective, by examining interactions between FP clinic staff and their clientele. "Simulated" clients were sent to 16 FP clinics in Kathmandu to request information and advice. The study revealed that in the impersonal setting of a family planning clinic, clients and staff fall into traditional, hierarchical modes of interaction. In the process, the client's "modern" goal of limiting her family size is subverted by the service system that was created to support this goal. Particularly when status differences are greatest, that is, with lower-class and low caste clients, transmission of information is inhibited.

This study reports research conducted in a rural Nepalese Hindu Community to examine three questions: (1) the nature of family structure of the elderly roughly 4 decades ago; (2) whether the family structure at that time was the same for high and low castes; and (3) whether the past situation differs from that today. Four decades ago 78% of elderly high caste males were living in the ideal Hindu joint family structure compared with only 24% of the low castes. Today just 50% of the high castes and 42% of the low castes live in joint families. The difference in the past derives from access to and control over economic resources. Economic changes since 1950 have increased access to economic resources and altered the family structure of the high castes but not the low castes.

The ability of freshly collected and frozen human spermatozoa to migrate in round capillary tubes containing specially formulated polyacrylamide gel was investigated, using 33 ejaculates from 27 donors. Each semen sample was divided; one portion was left undiluted, and the other portion was diluted to 50 x 10(6) sperm/ml. Glycerol was used as the cryoprotectant. The percentage of motile sperm cells was determined before and after freezing. Fresh semen contained a higher percentage of motile cells, which migrated farther than those of cryopreserved-thawed semen. Various correlations between the percentage of motile sperm and migration distance ranged from 0.57 to 0.62. There was a low positive correlation of migration distance with sperm cell concentration per milliliter, r = 0.25 to 0.34; and thus adjusting semen samples to a standard sperm concentration improved the accuracy of the test only slightly. The regression coefficient of migration distance on the percentage of motile sperm in fresh semen was 0.65, indicating that for each 10% increase in sperm motility, migration distance is predicted to increase 6.5 mm. Five batches of polyacrylamide gel gave uniform results, and the application of this stable gel to fertility investigations is discussed.

There is no malocclusion in the adult that cannot be treated as well with esthetic appliances as with the conventional metal brackets. In a study about adult orthodontic patients. Breece and Nieberg found that most people wait until they are adults to start treatment because no one recommended it previously. It is essential that the dental practitioner understand the positive psychological impact of esthetic appliances upon the attitude of the adult and recommend that the adult needing orthodontic treatment enjoy the benefits of these technologic advances in esthetics and comfort.

This paper suggests a conceptual framework for the cross-cultural study of dependency in order to encourage and facilitate data-based cross-cultural comparisons. It offers an etic, operational definition encompassing biological, activity and economic components. It also emphasizes that the emic definition is crucial for understanding a situation. The utility of distinguishing several components of an etic definition of dependency and distinguishing etic from emic definition is illustrated using the examples of Sherpas in Helambu, Nepal. From the etic viewpoint, the Sherpas are apparently healthy, economically productive and physically active and therefore lie near the independent end of the dependency continuum. The recent emigration of many young adults has produced a demographic situation where few elderly can achieve their expectation of growing old while sharing their own households with their youngest son and his family. Although family life is valued and most elderly Sherpas have other offspring and other relatives in the village, the majority of elderly Sherpa live alone and express dissatisfaction at doing so. From their standpoint, reliance upon someone other than the youngest son for lodging or food is considered prejoratively and as dependency. Their emic definition of dependency is different from the Western definition and both differ from what we have referred to as etic dependency.

Tooth movement into a suspected area of periodontosis is possible if sufficient time is allowed for filling of the socket. This report describes a 19-year-old woman with periodontosis who had orthodontic therapy and periodontal surgery five years after the initial examination. The disease was arrested and occlusion established through the combined approach of orthodontic and periodontic treatment.

This paper describes age differences in sensory and cognitive function in a cross-sectional sample of 117 Nepalese men aged 50 to 88 years living in a traditional agrarian society. The prevalence of impairment of vision, hearing, vibration sensitivity, and cognitive function is progressively higher in successively older age categories in this society as it is in Western industrial societies. This has practical consequences for everyday life. Men with vision impairment are less likely to retain the esteemed social role of head of an extended household. Men with visual and hearing impairment leave their household compounds less frequently, have less frequent social contacts outside their households, and remain inactive a greater proportion of the time. In this technologically simple society without modern medical remedies, vision and hearing impairments are associated with social roles and daily activity patterns that foster economic and political dependence and social isolation.

This paper reports the results of a natural experimental test of the hypothesis that elderly residents of rugged terrains are more physically fit than their counterparts in flat terrains due to the additional lifelong daily exertion occasioned by the inescapable need to walk up and down steep slopes. Cycle ergometer tests of physiological response to work were undertaken by two groups of high caste Hindu male farmers, aged 50 to 79, living in Central Nepal. One comprised an experimental group resident in rugged terrain and the other a control group resident in flat terrain. No differences in heart rate and blood pressure measured at submaximal workloads, at peak effort, or during recovery from exercise were demonstrated. Measurements of physical exertion revealed that few people in either terrain engaged in activity sufficiently strenuous to raise heart rates to a level where training could occur. Despite a rural agricultural lifestyle, these men were not especially physically fit.

Currently the majority of the world's elderly reside in less developed countries and their proportion is increasing. This paper presents evidence that the process of modernization can have a negative impact on the elderly in even the most remote rural Third World settings, even though those settings are not modernized or in the process of modernization in any of the normal uses of that concept. Fieldwork was conducted in Helambu, Nepal on a sample of 37 persons over the age of 50 that included 86% of population aged 60 and over. Despite high levels of activity, health, social and economic status, the elderly were greatly dissatisfied with their situation. The paper demonstrates the manner in which modernization in India has profoundly changed household/family organization in Helambu and produced this situation.

Recent data from Nepal indicate that in the urban areas reproductive attitudes are changing much more rapidly than behavior, resulting in many unwanted births. Based on transcripts from in-depth interviews conducted in 1982 by the Urban Fertility and Contraceptive Use Project, this article analyzes the "contraceptive lag" in urban Nepal by examining contraceptive decision-making among urban couples in Kathmandu. Tracing links between attitudes, knowledge, values, and specific behavioral outcomes, the analysis reveals that for the majority of the couples in the study, unwanted births occurred for reasons that might have been obviated through more effective provision of family planning services.

This paper examines the relationship between physical fitness and activity among elderly males in the traditional rural community of Chetbesi, Nepal. It takes advantage of the unique character of the Hindu caste system to implement a quasiexperimental research design that approximates random assignment to high and low activity levels. The members of the Sarki caste have lower heart rates and systolic blood pressure, relative to other castes, at each of three submaximal workloads and during recovery from bicycle ergometer exercise. Direct observation and physiologic monitoring show that the Sarkis engage in more frequent and extended periods of heavy labor. Thus intracohort variation in physical fitness and activity patterns among the Chetbesi elderly is a function of birth into a socially defined group rather than of self-selection. This pattern of differential fitness may typify the process of aging in many stratified traditional and modernizing societies where socially delimited segments of the population perform the bulk of the hard work. Intrapopulation differences aside, comparison of Sarkis and non-Sarkis with other samples reveals that both lie within the reported range of variation. The rural, unmechanized, agricultural lifestyle and mountain environment of Chetbesi do not result in exceptional fitness for residents. The Chetbesi data suggest that the popular notion that aging is less debilitating in traditional agrarian societies located in rugged mountain terrains may be a myth. The demonstration of the influence of social forces on physical fitness suggests that future research might concentrate profitably on identifying social structures that produce high levels of physical fitness.

This paper questions the implicit assumption derived from modernization theory that elderly persons in the Third World lead secure and satisfying lives because they still live in extended families. Data from elderly Hindus living in Kathmandu, Nepal, are presented and demonstrate that, although these elderly people do continue to live in extended families, social and economic changes have transformed the nature of intergenerational social relations within these families to the detriment of the elderly family members.

Seventy-nine men with Hodgkin's disease were treated with chemotherapy protocols at Memorial Sloan-Kettering Cancer Center and had pretreatment semen analysis performed at the area semen bank. The patients were evaluated to determine: the quality of pretreatment semen, the effect of treatment on spermatogenesis, and the success rate of artificial insemination after semen cryopreservation. Pretreatment sperm concentration, fresh motility, fresh progression, postthaw motility and postthaw progression were all significantly decreased in men with Hodgkin's disease compared with normal controls. Posttreatment semen analysis in 44 men showed azoospermia in 80%, sperm concentration, less than or equal to 10 X 10(6)/mL in 11%, and sperm concentration greater than 10 X 10(6)/mL in 9%. Eleven couples attempted artificial insemination using cryopreserved semen, thus far resulting in three pregnancies. Semen cryopreservation and artificial insemination offer a partial solution to posttreatment azoospermia in this population, but further methods are needed to minimize gonadal toxicity without compromising therapy for Hodgkin's disease.

This paper presents data on the hemoglobin concentration of a sample of 103 pastoral nomads who are lifelong residents of Phala, at 4,850-5,450 m, on the northern plateau of the Tibet Autonomous Region of the Peoples' Republic of China. This native population resides at the highest altitude of which we are aware and is thus exposed to the most extreme chronic hypoxic stress. However, they do not exhibit the most pronounced physiological adaptations, i.e., hemoglobin concentrations exceeding those found in all other high-altitude populations. Adult male and female mean hemoglobin concentrations of 18.2 and 16.7 gm/dl, respectively, were found. These data, in conjunction with earlier studies of ethnic Tibetans living at 3,400 m, demonstrate a pattern of increasing hemoglobin concentration (erythrocytosis) at increasing altitude of residence in the Himalayas and Tibet. At the same time, however, the hemoglobin concentration is lower than that found among Andean highlanders. These new data raise the possibility of quantitative population differences in hematological adaptation to high altitude hypoxia.