Human cold adaptation: an unfinished agenda

1975 marked the end of a 20-year period of human biology research on physical environment. The focus then shifted from climatic adaptation to problems of nutrition, disease, and stress. However, many questions about human environmental patterns, especially in reference to their evolution, were abandoned rather than resolved. Assumptions about cold protective functions of low surface area/body mass ratio are entrenched in physical anthropology, despite lack of experimental validation. Since heat loss is controlled by vasoregulation and tissue insulation, a simple physics model of SA:mass may not apply. The issue merits investigation, as do the assumed thermal advantages of foreshortened extremities. Physiological assessment remains our primary research tool. In cold climate natives, elevated basal metabolic rates now appear to be genetically induced. During cold exposure, the body manages heat conservation through well known channels but also by specialized thermogenic functions such as metabolism in brown adipose tissue (BAT). The powerful protective capacity of BAT is largely unexplored either within or between populations of cold exposed human adults. An irony of our profession is that many biological variables seem to have minor effects when compared to behavioral cold protections. This is partly because biological anthropologists may have made incorrect assumptions about what most threatens the well being of cold climate people. Contrasts in environmental behaviors when comparing northern cultures such as Inuit, Athabaskan, and Norse are particularly instructive. Adaptations to life in the cold may ultimately reveal their secrets through biocultural research design modeling of environmental research. With both practical and theoretical gains still wide open, the field needs renewed attention from human biology.

Developmental response to cold stress in cranial morphology of Rattus: implications for the interpretation of climatic adaptation in fossil hominins

Adaptation to climate occupies a central position in biological anthropology. The demonstrable relationship between temperature and morphology in extant primates (including humans) forms the basis of the interpretation of the Pleistocene hominin Homo neanderthalensis as a cold-adapted species. There are contradictory signals, however, in the pattern of primate craniofacial changes associated with climatic conditions. To determine the direction and extent of craniofacial change associated with temperature, and to understand the proximate mechanisms underlying cold adaptations in vertebrates in general, dry crania from previous experiments on cold- and warm-reared rats were investigated using computed tomography scanning and three-dimensional digitization of cranial landmarks. Aspects of internal and external cranial morphology were compared using standard statistical and geometric morphometric techniques. The results suggest that the developmental response to cold stress produces subtle but significant changes in facial shape, and a relative decrease in the volume of the maxillary sinuses (and nasal cavity), both of which are independent of the size of the skull or postcranium. These changes are consistent with comparative studies of temperate climate primates, but contradict previous interpretations of cranial morphology of Pleistocene Hominini.

Physiological anthropology: past and future

Environmental studies in adaptive human biology by North American anthropologists have a history of strong investigative research. From both laboratory and field work, we have gained major insights into human response to physical and social challenges. While these results were considered by most professionals to belong within evolutionary biology, in fact the intellectual structure sprang almost entirely from physiological equilibrium models. Consequently, physiological process itself was the focus. Further, most of the physiological patterns were not linked directly to important outcomes such as work output, reproductive success or survival. About 1975, American physiological anthropologists, led by Paul Baker, turned to studies of health, change and stress response. These studies were strong, but were still neither genetic nor evolutionary in intellectual structure. Evolutionary human biology was taken over by a new body of theory now called "behavior ecology", positing that selfish genes control human behavior to promote their own reproduction. This was paralleled by strong use of evolutionary theory in some areas of molecular biology. However, although physiological anthropologists have not focused on evolution, we have been developing powerful causal models that incorporate elements of physiology, morphology, physical environment and cultural behavior. In these "proximate" biocultural models, it is of little importance whether outcomes such as work or energy management are genetically based. Our future offers two major challenges. First, we must confirm causal links between specific physiological patterns and outcomes of practical importance to individuals and societies. Second, if we are to take our place in evolutionary biology, the one overarching theory of life on earth, we must understand the heritability of physiological traits, and determine whether they play a role in survival and reproduction.

Climate, racial category, and body proportions in the U.S

In 1955, Newman and Munro reported correlations between physical characteristics and climate in a white male U.S. Army sample. For example, the body weight-to-mean annual temperature correlation was -0.460. Because the men descended from relatively recent immigrants to North America, physical clines implicitly derived from differential lifetime growth rather than from natural selection. Consequently, both causation and adaptive function of Bergmann's and Allen's biogeographic rules in humans were called into question. Analysis of male and female data from the 1988 U.S. Army anthropometric survey offers new insights to the 1955 study findings. Using state means of the male subsample identifying themselves as white, as did Newman and Munro, no significant correlations were found between climatic variables and height, weight, BMI, or other body proportions. With individual data rather than state mean values, neither white male nor white female samples showed morphology to climate correlations. Relationships seen in the earlier white sample have disappeared, possibly due to a more uniform growth environment and mobility in the U.S. Black males and females showed some body trait to climate correlations but only at r values of around 0.10. Using state means from the combined sample (racial identification ignored), strong correlations are seen. As examples, mean annual temperature correlates to male relative sitting height at r = -0.634 and to female relative forearm length at r = 0.645. However, these values are evidently spurious, being products of the higher percentages of whites enlisting from colder areas of the U.S.

Neandertal cold adaptation: physiological and energetic factors

European Neandertals employed a complex set of physiological cold defenses, homologous to those seen in contemporary humans and nonhuman primates. While Neandertal morphological patterns, such as foreshortened extremities and low relative surface-area, may have explained some of the variance in cold resistance, it is suggested the adaptive package was strongly dependent on a rich array of physiological defenses. A summary of the environmental cold conditions in which the Neandertals lived is presented, and a comparative ethnographic model from Tierra del Fuego is used. Muscle and subcutaneous fat are excellent "passive" insulators. Neandertals were quite muscular, but it is unlikely that they could maintain enough superficial body fat to offer much cold protection. A major, high-energy metabolic adaptation facilitated by modest amounts of highly thermogenic brown adipose tissue (BAT) is proposed. In addition, Neandertals would have been protected by general mammalian cold defenses based on systemic vasoconstriction and intensified by acclimatization, aerobic fitness, and localized cold--induced vasodilation. However, these defenses are energetically expensive. Based on contemporary data from circumpolar peoples, it is estimated that Neandertals required 3,360 to 4,480 kcal per day to support strenuous winter foraging and cold resistance costs. Several specific genetic cold adaptations are also proposed--heat shock protein (actually, stress shock protein), an ACP*1 locus somatic growth factor, and a specialized calcium metabolism not as yet understood.

Mapping toxin exposure risk due to children's play: a case study

During the 1920's and 1930's, a Niagara County, New York residential community, Belden Center, developed in tandem with two adjacent toxic waste disposal sites. During the period that they were in use, both sites were classified as public health hazards. Particularly between 1944 and 1979, as toxins were deposited, neighborhood children swam and played throughout the industrial waste sites. By reference to a large-scale map of the dumps, present residents described locations and types of play during their childhood. Assuming that a child would play away from home between 8 and 19 years of age, this allowed identification of cohorts that used the sites during different periods. An outcome map showing sites, dates, and types of play is the primary product of this investigation. More boys than girls played in the dumpsites, and we identified a subsample that did not use them for play. We conclude that children's play should be considered a major source of risk where communities lie next to toxic waste sites.

Field test of self-paced work capacity: Ifugao rice farmers

This article reports results of a field test of work capacity on 30 male farmers ranging in age from 15-54. It involved a self-paced walk from the valley floor, up the mountain wall, and return, with heart rate monitoring. The route was 2.21 km long with a vertical rise of about 200 m. At its steepest, the grade was about 34 degrees, requiring long runs of steps cut into the mountain face. The purpose of this research was to determine whether biological and behavioral traits of individual men help to explain household economic productivity to which they contribute. The traits included anthropometry and a new measure of self-paced, voluntary work capacity (heart rate x time). Income per productive adult increased as did the relative fitness index (heart rate increase above resting x min taken to finish the course). However, the number of rice bundles earned per family, expected to increase with more fit workers, increased with the number of household adults and sitting height (adjusted R(2) = 0.392), but not with self-paced fitness markers. Am. J. Hum. Biol. 12:192-200, 2000. Copyright 2000 Wiley-Liss, Inc.

The China Productivity Project: results and conclusions

Experiments were conducted to determine what factors cause variation in individual work output (economic productivity). Forty-five young male Chinese cycle haulers from Beijing were assessed for physiological work capacity, size and body composition, health, nutritional status, cold resistance, household social environment, and motivation. Experiments were conducted in the laboratory as well as under actual working conditions; ethnographic observations were made in the household and on the job during the Beijing winter of 1992. Overall work motivation correlated to actual monthly distance/load measures of productivity the most strongly (r = 0.518), followed by physiological capacity estimated by heart rate:speed ratio during field experiments (r = -0.473). Alcohol consumption (a negative factor), household health, and carbohydrate intake were all moderate predictors. Maximum oxygen uptake showed lower correlation (r = 0.261), and among anthropometric values only relatively long lower legs were predictive (r = 0.298). Since many of these variable categories were relatively independent of each other, multiple regression analysis showed that together they explained 61.6% of the work output variance. Simultaneous prediction by FASEM (LISREL) is also very strong.

An universal model of health and work output: theoretical structure and testing strategy

The model proposed in this paper presents a broad range of factors to predict individual human work output. The predictors include aerobic capacity, body size, motivation, work pattern, social environment and social network, caloric intake, drug and alcohol use, stress resistance and thermoregulation. Health is a major intervening variable, and its relationship to work output is a special concern of this research. We suggest that this model may be used as a template to explain human productivity in most societies. Its universality can be subjected to rigorous testing in a range of settings from tropical upland swidden horticulturalists to urban workers in a northern industrialized country. Observations are offered on some of those testing sites and on methodological issues implicit in research of this breadth. A major pilot study of urban Chinese workers has already demonstrated the predictive power of the model in one setting.

Work performance of Chinese cycle haulers: controlled field experiments in normal work conditions

Forty-five male Chinese cycle haulers performed a controlled field experiment under mild winter conditions. The objective was to gain insight into factors that affect work performance. Each man hauled the same 481-kg load around a Beijing street course of 14.18 km. The experiment was a measured sample of the same work they do routinely, on the same roads, using similar human powered hauling cycles (modified only enough to carry observers and instruments). The course was completed at a mean speed of 10.4 kph and mean time of 84.2 min. While there was considerable variation in individual pace and in pace change during work, the haulers performed at relatively high output in reference to their capacities. Mean heart rate was 156.8 +/- 16.1 bpm, 83.9% of maximum. The men had average body build and were average in size for the general Chinese population (X stature = 169.7 cm) although they showed relatively high aerobic capacity (determined in laboratory tests). Performance levels during experiments appear to match habitual work patterns, and self-pacing emerged as a major behavioral finding of this research. Speed, a primary index of job performance, showed significant correlation to heart rate, VO2max, variation in windchill, self-reported health and other variables, with a multiple regression coefficient of 0.811. Similar patterns were seen for heart rate relative to speed, except that physical size, education, and other behavioral variables were also predictors.

Physical size, school performance, and visual-motor maturity in the Philippines

The broad theoretical issue approached in this work is whether supposedly adaptive or maladaptive biological variation has any real impact on people's lives and well-being. From a poor barrio of a rural lowland Philippine fishing community, a sample of 25 boys and 25 girls who had completed first grade at 8 years was measured. This population may be considered moderately undernourished by NCHS but not Philippine standards. Correlations between anthropometry, school grades, and visual-motor skills were calculated. Grades, taken here to have both cognitive and social-behavioral components, correlated best to percentage of median height (NCHS and Philippine), less strongly but still significantly to visual motor skill, and not to weight for height. Visual-motor skills (estimated by the Beery VMI) did not correlate to anthropometry. Visual-motor performance, however, is low by U.S. standards, a finding discussed in a behavioral context.

Stature in an early mid-19th century poorhouse population: Highland Park, Rochester, New York

If the early 19th century United States was a developing country, then it may be expected that the lowest economic stratum would show some biological consequences of poverty. This report examines that question by estimating stature on 90 male and 64 female adult skeletons from an unmarked cemetery dating between 1826 and 1863. The Highland Park burial ground was adjacent to institutions which interned unfortunates of Rochester, Monroe County, in western New York. The best estimate of male stature (N = 84) is 172.6 cm. A review of other 18th and 19th century height data shows this value not to be relatively stunted, but rather exactly on the predicted mean of its time. If this was a poor population, stunting was not a consequence of poverty. Females (N = 59) showed a best height estimate of 160.0 cm. Less comparative data are available, but this too seems average for the time. A brief discussion of secular trends, changing income inequity and fluctuating stature from the 18th through 20th centuries puts this finding in context.

Stature variation in the British American Colonies: French and Indian War records, 1755-1763

Personnel records kept by military units of American colonials during the French and Indian War (1755-1763) are analyzed for relationships between environmental factors and stature. A robust American economy and direct access to high-quality food were apparently critical to tallness of this white American male sample. American-born men were taller at all ages than those who had migrated from Europe. January temperatures, rural versus urban birth, and ethnicity also showed stature relationships within the American-born group; thermal effects were by far the strongest of the non-nutritional factors.

Skeletal stature compared to archival stature in mid-eighteenth century American: Ft. William Henry

Fourteen soldiers buried at Ft. William Henry, New York, between 1755 and 1757 are compared for stature to a sample of 2,232 New York Provincial soldiers measured anthropometrically in 1760. The William Henry stature mean of 177.3 cm is significantly higher than that of the Provincials (169.7 cm), and their variation of stature is significantly lower-suggesting that the cemetery population was a select group. A historical explanation is offered for this unexpected finding.

Human nasal protrusion, latitude, and climate

Relationships between morphological features of human skeletal nasal protrusion, latitude, and climate were investigated. Craniofacial dimensions and indices determined by Woo and Morant (1934) on a world sample of 55 skeletal populations were used as dependent variables. Sample sizes were as low as 39 in some calculations because either skeletal or geographic data were missing. Thirteen climatically related averaged variables, for each population's provenience, were the independent variables. Multivariate techniques of bivariate correlation, multiple regression, and partial correlation were applied. A strong, Statistically significant cline of increasing nose protrusion, with decreasing absolute humidity and with increasing latitude, was found. Cold climatic variables appeared to be of greater importance than warm measures. Similarly, absolute humidity was found to be a much better predictor of nose protrusion than was relative humidity.

Human facial temperatures in natural and laboratory cold

Asian, European, and American Indian men were subjected to craniofacial cooling to determine relative ranking and temperature curves for various facial skin sites. Moving and still air 0 degrees C to -35 degrees C in both laboratory and subarctic outdoor settings were used. The objective was to examine resistance to facial frostbite. Facial temperatures stabilize well above freezing even under quite cold conditions and this conclusion is congruent with low incidences of facial frostbite. Racial differences in face temperatures were clearly shown at only the malar eminence, and there was some evidence that exercise can be used to enhance facial circulation. These results and those of other studies reviewed demonstrate that facial sites cooled by convection are usually ranked from forehead (warmest) through malar, cheek, and chin, to nose (coldest). When cooled by still air, the sites tend to retain that same ranking, but there is more variation in ranking.