Predictors of milk cortisol in North American women.

OBJECTIVES: Human milk content varies across mother-child dyads, environments, and populations. Among the hormones in milk is cortisol, a glucocorticoid; its impact on the breastfeeding child is unknown. Milk cortisol may constitute a signal to the child's developing physiology which can shape characteristics (e.g., growth, temperament) to prevailing environmental conditions. This exploratory study evaluated the maternal, breastfeeding, and infant characteristics associated with milk cortisol. METHODS: We evaluated archived milk specimens for cortisol using enzyme immunoassay and employed an information-theoretic approach to assess associations between milk cortisol and participant characteristics with linear regression modeling. Because we employed secondary data, information for some variables likely to impact milk cortisol variation (e.g., time of day, socioeconomic status, maternal or infant body mass index, milk energy density) was unavailable. RESULTS: Participants were 48 lactating mothers from upstate New York, aged 21-40 years. Milk cortisol ranged from 0.098 to 1.007 µg/dL. Child age ranged from 1 to 26 months. In linear regression employing best fit modeling criteria, milk cortisol increased with child age (B: 0.069; p: .000; a 7.1% increase in milk cortisol for each month of child age), while child symptoms of illness (B: -0.398; p: .057; a 33% decrease) and consumption of complementary foods (B: -.525; p: .020; a 41% decrease) were associated with lower milk cortisol. CONCLUSIONS: We speculate that increasing milk cortisol with child age plays a role in signaling development (e.g., as increasing independence increases risk for injury and other negative health outcomes), independent of the maternal stressors we could capture.

Evolutionary Strategies for Body Size.

Humans show marked variation in body size around the world, both within and among populations. At present, the tallest people in the world are from the Netherlands and the Balkan countries, while the shortest populations are central African Pygmies. There are genetic, genetic plasticity, developmental, and environmental bases for size variation in Homo sapiens from the recent past and the present. Early populations of Homo species also have shown considerable size variation. Populations from the present and the past are also marked by sexual dimorphism, which, itself, shows group variation. There is abundant evidence for the effects of limited food and disease on human growth and resultant adult body size. This environmental influence has been reflected in "secular trends" (over a span of years) in growth and adult size from socioeconomic prosperity or poverty (availability of resources). Selective and evolutionary advantages of small or large body size also have been documented. Heritability for human height is relatively great with current genome-wide association studies (GWAS) identifying hundreds of genes leading to causes of growth and adult size variation. There are also endocrinological pathways limiting growth. An example is the reduced tissue sensitivity to human growth hormone (HGH) and insulin-like growth factor (IGF-1) in Philippine and African hunter-gatherer populations. In several short-statured hunter-gatherer populations (Asian, African, and South American), it has been hypothesized that short life expectancy has selected for early maturity and truncated growth to enhance fertility. Some island populations of humans and other mammals are thought to have been selected for small size because of limited resources, especially protein. The high-protein content of milk as a staple food may contribute to tall stature in East African pastoral peoples. These and other evolutionary questions linked to life history, male competition, reproduction, and mobility are explored in this paper.

Coming to grips with economic development: Variation in adult hand grip strength during health transition in Vanuatu.

OBJECTIVES: To determine whether (1) maximal handgrip strength (HGS) is associated with inter-island level of economic development in Vanuatu, (2) how associations between island of residence and HGS are mediated by age, sex, body size/composition, and individual sociodeomographic variation, and (3) whether HGS is predictive of hypertension. MATERIAL AND METHODS: HGS was collected from 833 adult (aged 18 and older) men and women on five islands representing a continuum of economic development in Vanuatu. HGS was measured using a handheld dynamometer. Participants were administered in an extensive sociobehavioral questionnaire and were also assessed for height, weight, percent body fat, forearm skinfold thickness, forearm circumference, and blood pressure. RESULTS: HGS was significantly greater in men than in women regardless of island of residence. HGS was also significantly positively associated with inter-island level of economic development. Grip strength-to-weight ratio was not different across islands except in older individuals, where age-related decline occurred primarily on islands with greater economic development. HGS significantly declined with age in both men and women. CONCLUSION: HGS is positively associated with modernization in Vanuatu, but the relationship between HGS and modernization is largely due to an association of both variables with increased body size on more modernized islands. Further research on the role of individual variation in diet and physical activity are necessary to clarify the relationship between HGS and modernization.

Physical anthropology in 1918 and the founding of the U.S. journal.

In 1918, the first issue of the American Journal of Physical Anthropology was prepared and distributed by Ales Hrdlicka, the Curator of Physical Anthropology at the Smithsonian Institution. This was a singular act, both in the general and specific sense. It was the first journal of physical anthropology published in the United States, and it was a sole effort by Hrdlicka, who was committed to promoting and recognizing physical anthropology as a new science in America. On this 100th anniversary of the founding of the journal, Hrdlicka's efforts were successful: physical/biological anthropology is a strong and timely discipline that represents a major area of scientific research today.

Grip strength and body composition in Turkana pastoralist children and adolescents.

OBJECTIVES: In an earlier study, age changes and sex differences in grip strength were documented for adult Turkana pastoralists of Kenya (Little and Johnson, 1986). The objective here is to characterize age changes and sex differences in grip strength of Turkana children and adolescents in the context of arm lean tissue composition, and in comparison with other African, African-American, and non-Western populations. METHODS: Anthropometric measurements, derived body composition values, and grip strength measures (maximum voluntary contraction) were taken on a sample of 232 nomadic Turkana pastoralist children (94 boys and 138 girls) aged 3 to 21 years. Relationships were tested between grip strength (in Newtons) and mid-upper arm (brachium) lean tissue cross-sectional areas. Comparisons were made among several different ethnic groups. RESULTS: Turkana children and adolescents had low arm muscle (derived lean tissue) and grip strength values when compared with U.S. NHANES percentile references. Girls' percentile rankings were greater than boys' percentile rankings for muscle and for grip strength. Both boys and girls were intermediate when compared with other non-Western populations and U.S. strength grip reference values. Correlations between grip strength and arm lean tissue areas were highly significant for both boys and girls. CONCLUSIONS: The greater relative muscle size and grip strength values of late adolescent girls compared to boys is consistent with an earlier study of adults. The difference is likely to result from greater physical subsistence activity and greater access to food in girls than in boys. Several suggestions are given to explain why Turkana youths have relatively small muscle sizes.

A half century of high-altitude studies in anthropology: introduction to the plenary session.

Until 50 years ago, high-altitude terrestrial research was conducted largely within the realm of environmental physiology, where interests were focused on physiological mechanisms and mountain exploration. Scientists from the United States, Europe, and Peru had developed sophisticated physiological models of adaptation and acclimatization to the hypoxia of high altitude, but very little research had been conducted on permanent residents, particularly natives of high altitude in the two major regions of the world-the Andes and the Himalayas. In 1962, Raul T. Baker initiated a project at the Pennsylvania State University to explore the responses of indigenous Peruvians to the major stresses at altitude: hypoxia and cold. Approaches to this early research were anthropological in perspective and centered on population-level studies with an evolutionary approach. Studies were conducted by applying a combination of physiological experimental methods, simulated field experiments, and extended anthropological field observations. Early hypotheses at this time were that heredity played a major role in the adaptive complexes in native high-altitude residents. These early hypotheses were later modified to incorporate or replace the genetic hypotheses with developmental adaptation models. A half century of research within anthropology and research in other fields has presented a vastly more complex and integrated picture of high-altitude adaptation in native residents. Recent studies incorporate physiology and oxygen transport, population and molecular genetics, reproduction, growth, and development. The history and current status of high-altitude research and its anthropological applications are treated in papers from this plenary symposium.

Joseph S. Weiner and the foundation of post-WW II human biology in the United Kingdom.

Both the United States and the United Kingdom experienced a transformation in the science of physical anthropology from the period before World War II until the post-war period. In the United States, Sherwood L. Washburn is credited with being a leading figure in this transformation. In the United Kingdom, two individuals were instrumental in bringing about a similar change in the profession. These were Joseph S. Weiner at the University of Oxford and Nigel Barnicot at the University of London, with Weiner playing the principal role as leader in what Washburn called the "New Physical Anthropology," that is, the application of evolutionary theory, the de-emphasis on race classification, and the application of the scientific method and experimental approaches to problem solving. Weiner's contributions to physical anthropology were broad-based--climatic and work physiology, paleoanthropology, and human variation--in what became known as human biology in the U.K. and human adaptability internationally. This biographical essay provides evidence for the significant influence of J.S. Weiner on the post-war development of human biology (biological or physical anthropology) inthe U.K.

Raymond Pearl and the shaping of human biology.

Raymond Pearl (1879-1940) was a significant figure in the field of biology. He founded the journal Human Biology and almost single-handedly promoted and established the scientific discipline of human biology. His scientific versatility was one of his most important features during the first four decades of the 20th century, and he played a major role in developing the fields of biodemography, human population biology, human life-cycle and life span approaches, fertility, growth, the biology of longevity and senescence, and mortality. He was one of the earliest biologists to combine biometric analyses and experimental studies to explore the dimensions of human biology. Pearl also was broadly educated in the arts, music, literature, history, the classics, and science. His writing was sophisticated and often witty, and his views were sometimes provocative and controversial. His network of colleagues and friends among the literary and science worlds was substantial. The following biographical memoir of Raymond Pearl is designed to commemorate the 80th anniversary of the founding of his journal Human Biology and is a tribute to this great scientist. Pearl's sudden death at age 61 truncated a scientific career that was one of the most productive of the 20th century.

Blood pressure and lifestyle on Saba, Netherlands Antilles.

During the 20th century, infectious disease morbidity and mortality generally waned whereas chronic degenerative diseases posed a growing burden at the global level. The population on Saba, Netherlands Antilles has recently experienced such an epidemiologic transition, and hypertension was reported to be extraordinarily high, although no prevalences have been reported and relationships with lifestyle factors associated with rapid modernization have not been explored. In this study, a medical and demographic questionnaires, as well as body composition and blood pressure measures were collected from 278 Saban men and women aged 18-91 years. When age and sex adjusted, 48% of the population was hypertensive. Age, BMI, and Afro-Caribbean descent were all associated with higher blood pressures. In a second phase, 124 individuals of the 278 were invited to receive a longer questionnaire on individual exposure to modernizing influences such as travel and education. Higher blood pressure was associated with having lived in fewer different places in the past; those who stayed only on Saba or Statia had higher blood pressures than those who had also lived in more modernized areas. However, this was no longer statistically significant after adjustment for age and BMI. Lifestyle incongruity was positively associated with higher blood pressure in that those with more discord between material wealth and income were more likely to be hypertensive, and this remained statistically significant after adjustment for age and adiposity. In summary, hypertension is highly prevalent on Saba and tended to be associated with greater age, adiposity, Afro-Caribbean ancestry, and lifestyle incongruity.

Juan Comas's summary history of the American association of physical anthropologists (1928-1968).

This translation of Juan Comas's Summary History of the American Association of Physical Anthropologists was originally published in Spanish by the Instituto Nacional de Antropología e Historia, Mexico, in 1969 (Departamento de Investigaciones Antropológicas, Publication 22). Physical anthropologists from North America and members of the American Association of Physical Anthropologists owe Juan Comas a debt of gratitude for having labored to produce this Summary History of the AAPA. There is much useful and interesting material in this document: extensive endnotes that are helpful to the historian of the profession; an appendix of the Journal issues where the proceedings of annual meetings can be found; a detailed listing of contributors of papers to annual meetings from 1930-1968; a warm acknowledgment and history of the contributions of the Wenner-Gren Foundation to biological anthropology; a history of the Yearbook of Physical Anthropology; and comments on the short-lived PA Newsletter. In addition, there are appendices with the founding AAPA Constitution and By-Laws from 1930 and as they existed in 1968. All of this synoptic information saves the reader with interests in the history of the AAPA considerable effort, especially when few university and college libraries have the full (old and new) series of the AJPA on their shelves. We have tried to provide a translation of Comas's history that is faithful to the original Spanish-language publication. In a few cases, we shortened sentences and applied a slightly more modern usage than was popular in the late 1960s.

Pubertal timing, hormones, and body composition among adolescent Turkana males.

The Turkana, like other East African pastoral groups, are known for their tall adult stature, achieved despite a blunted growth spurt during adolescence and continued growth into the early 20s. To investigate the hormonal mechanisms associated with the pattern of slow and continued adolescent growth, we collected data on hormonal status, height, weight, and trunk skinfolds and ethnographic self-reports of testicular maturation in a cross-sectional sample of 35 nomadic and 37 settled Turkana males aged 14-24. Hormonal determinations included testosterone (T), sex hormone-binding globulin (SHBG), and dehydroepiandrosterone (DHEA) in blood, in addition to urinary DHEA. Self-reports of testicular maturation showed no difference between settled and nomadic subpopulations. However, nomadic boys exhibited significantly higher levels of T, DHEA, and SHBG. Of all the hormones, only SHBG showed a significant relationship with age. Multiple regression models show blood T and SHBG to be significant independent predictors of achieved height as well as weight, controlling for age. Our results suggest that onset of puberty is substantially delayed among Turkana males, and that bioavailable T is related to growth in stature during adolescence. We suggest that SHBG acts to mediate the effects of energy availability on adolescent growth in this energetically limited population. Our findings may also have implications for understanding adolescent growth among Homo erectus.

A brief history of the Human Biology Association: 1974-2004.

Originally incorporated as the Human Biology Council in 1974, the Human Biology Association, as it has been known since 1994, has matured in the intervening 30 years to become a society that represents broadly the interests of human biologists in the U.S. and throughout the world. The purpose of this paper is to trace the development of the Association from its foundation to the present in the context of changes in the organization of the Association and in its By-Laws, officers, committees, and membership; the history of the two journals that served as the Association's official organs (Human Biology and American Journal of Human Biology); and how the annual meetings have evolved from a modest one-day plenary session to meetings that last more than two days and include a variety of scientific contributions. Highlights of the national meetings include the Raymond Pearl Memorial Lecture, the Franz Boas Distinguished Achievement Award, and the Edward E. Hunt, Jr. Student Prize.

History of migration studies in biological anthropology.

The earliest studies of human biological factors in migration in which a clear research design was employed date back to the early 20th century in the United States. Maurice Fishberg's study of Jewish migrants, published in 1905, antedated the classic study of Franz Boas initiated in 1908. There have been two main approaches. The first approach examined the impact of migration in relation to changing environment and the importance of environmental plasticity. For example, Fishberg reported that migrants had offspring different in stature from themselves and with differences thought to be due to improvements in the environment, although some selection of genetically determined traits was suggested. Subsequently, a number of research designs have been used, ranging from Boas's simple design of sedente (nonmigrant) adults and children compared with first- and second-generation migrants; Shapiro's extension of this study in Japanese migrants to Hawai'i; Goldstein's four-fold comparison of Mexican sedentes and their offspring in Mexico, and migrants to the USA and their offspring in the USA; and Lasker's extension of Goldstein's Mexican study by including comparison of sedentes with returning emigrants. More sophisticated designs were used by Harrison and Baker in examining altitude effects and changes in subsistence and lifestyle during the 1960s through to the 1980s. The second approach has focused on the effect of migration on gene flow. For example, the clinal variation of ABO blood groups in Europe and Australia is generally purported to result from past migration, although increasing random migration for blood groups is likely to eliminate clinal variation. Migration has usually been considered from a spatial (geographic) perspective, but more recent studies have also investigated the impact of social or occupational movement (social mobility) alone, or in combination with geographic migration, and tested whether such movements are selective or random for a number of biological traits.

Environmental stress and adaptational responses: consequences for human health outcomes.

With the dramatic pace of modernization of the world's population, human adaptation as a theoretical construct and paradigm will likely become a focal scientific issue involving scientists from many disciplinary areas during the 21st Century. Macro and micro environments are in rapid flux and human populations are exposed to rapid change. The concept of adaptation, at least in the field of biological anthropology and human biology, will likely remain tied to evolutionary processes and concepts of selection and fitness. In this paper, we discuss the theoretical constructs of adaptation and adaptability and select three current examples from our ongoing research that involve studies of adaptation and evolutionary processes in modernizing populations in different locations worldwide.

Energy reserves and parity of nomadic and settled Turkana women.

Members of the Turkana tribe include settled and nomadic peoples who reside in the southern part of Turkana District in the semiarid region of northwest Kenya. Nomadic Ngisonyoka Turkana keep livestock (camels, cattle, sheep, goats, donkeys), subsist principally on livestock products, and move camps frequently in search of forage for the livestock; settled Turkana cultivate foods along the principal rivers. Both nomadic and settled Turkana are subject to limited food resources on seasonal and long-term bases. Protein from meat, blood, and milk is sufficient in the diet, but food energy is limited, as are body fat reserves. Previous work has documented a decline in maternal adiposity with age in a large sample of the relatively lean nomadic women, and a negative association of fat stores with parity in a smaller sample of nomadic women. The problem of maternal depletion of fat energy reserves as a function of female reproductive history is explored in this study through anthropometry in a relatively large sample (N = 312) of nomadic and settled women. Both nomadic and settled women displayed some parity-related losses in fat stores. The relationship was stronger in the nomads, even after controlling for age. © 1992 Wiley-Liss, Inc.