Barry Bogin

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa

Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa. DOI: http://dx.doi.org/10.7554/eLife.09560.001

Evolution of the Human Life Cycle

Social mammals have three basic stages of postnatal development: infant, juvenile, and adult. Some species also have a brief female post‐reproductive stage. The human life cycle, however, is best described by five stages: infant, child, juvenile, adolescent, and adult. Women in both traditional and industrial societies may also have a long post‐reproductive stage. Analyses of bones and teeth of early hominids who died as subadults suggest that the evolution of the new life stages of childhood and adolescence are not of ancient origin. The current human pattern evolved after the appearance of Homo erectus. It is possible that evidence for the existence of the post‐reproductive stage for women will also be recoverable from the fossil record because the hormonal changes associated with menopause have profound effects on bone density and histology of tubular bones. It is hypothesized that the new life stages of the human life cycle represent feeding and reproductive specializations of the genus Homo.

Leg length, body proportion, and health: a review with a note on beauty.

Decomposing stature into its major components is proving to be a useful strategy to assess the antecedents of disease, morbidity and death in adulthood. Human leg length (femur + tibia), sitting height (trunk length + head length) and their proportions, for example, (leg length/stature), or the sitting height ratio (sitting height/stature × 100), among others) are associated with epidemiological risk for overweight (fatness), coronary heart disease, diabetes, liver dysfunction and certain cancers. There is also wide support for the use of relative leg length as an indicator of the quality of the environment for growth during infancy, childhood and the juvenile years of development. Human beings follow a cephalo-caudal gradient of growth, the pattern of growth common to all mammals. A special feature of the human pattern is that between birth and puberty the legs grow relatively faster than other post-cranial body segments. For groups of children and youth, short stature due to relatively short legs (i.e., a high sitting height ratio) is generally a marker of an adverse environment. The development of human body proportions is the product of environmental x genomic interactions, although few if any specific genes are known. The HOXd and the short stature homeobox-containing gene (SHOX) are genomic regions that may be relevant to human body proportions. For example, one of the SHOX related disorders is Turner syndrome. However, research with non-pathological populations indicates that the environment is a more powerful force influencing leg length and body proportions than genes. Leg length and proportion are important in the perception of human beauty, which is often considered a sign of health and fertility.

Language and life history: a new perspective on the development and evolution of human language

It has long been claimed that Homo sapiens is the only species that has language, but only recently has it been recognized that humans also have an unusual pattern of growth and development. Social mammals have two stages of pre-adult development: infancy and juvenility. Humans have two additional prolonged and pronounced life history stages: childhood, an interval of four years extending between infancy and the juvenile period that follows, and adolescence, a stage of about eight years that stretches from juvenility to adulthood. We begin by reviewing the primary biological and linguistic changes occurring in each of the four pre-adult ontogenetic stages in human life history. Then we attempt to trace the evolution of childhood and juvenility in our hominin ancestors. We propose that several different forms of selection applied in infancy and childhood; and that, in adolescence, elaborated vocal behaviors played a role in courtship and intrasexual competition, enhancing fitness and ultimately integrating performative and pragmatic skills with linguistic knowledge in a broad faculty of language. A theoretical consequence of our proposal is that fossil evidence of the uniquely human stages may be used, with other findings, to date the emergence of language. If important aspects of language cannot appear until sexual maturity, as we propose, then a second consequence is that the development of language requires the whole of modern human ontogeny. Our life history model thus offers new ways of investigating, and thinking about, the evolution, development, and ultimately the nature of human language.

Eight thousand years of economic and political history in Latin America revealed by anthropometry.

Human growth in height may be used as a cumulative record of the nutritional and health history of a person or a population, and often reflects the economic, social and political environment in which those people live. This paper explores the relationship between growth in height and the economic, social and political environment in Latin American populations. Adult height is analysed over an 8250 year period. It is shown that economic, social and political change prior to the European conquest of the Americas resulted in positive and negative trends in mean stature. Following the European conquest, there was a decline in mean adult stature in Middle and South America that continued until about 1939. From 1940 to 1989 there was a trend for increasing mean stature. A negative trend in stature for children is found in a second analysis. Economic decline and political unrest in Guatemala since 1978 is associated with a significant decline in the mean stature of 10- and 11-year-old children from families from very high, moderate, and very low socioeconomic status.

Plasticity, political economy, and physical growth status of Guatemala Maya children living in the United States

Migration of Maya refugees to the United States since the late 1970s affords the opportunity to study the consequences of life in a new environment on the growth of Maya children. The children of this study live in Indiantown, Florida, and Los Angeles, California. Maya children between 4 and 14 years old (n = 240) were measured for height, weight, fatness, and muscularity. Overall, compared with reference data for the United States, the Maya children are, on average, healthy and well nourished. They are taller and heavier and carry more fat and muscle mass than Maya children living in a village in Guatemala. However, they are shorter, on average, than children of black, Mexican-American, and white ethnicity living in Indiantown. Children of Maya immigrants born in the United States tend to be taller than immigrant children born in Guatemala or Mexico. Families that invest economic and social resources in their children have taller children. More economic successful families have taller children. Migration theory and political economy theory from the social sciences are combined with plasticity theory and life history theory (parental investment) from biology to interpret these data.

Measurement of growth variability and environmental quality in Guatemalan children.

The measurement of within-population growth variability may be a sensitive indicator of environmental quality. Specifically, it is hypothesized that within-population variability will increase in adverse environments. To evaluate this hypothesis the variability in stature growth of three samples of Guatemala school children (5-10 years old) is assessed. These samples include high socioeconomic status (SES) ladinos (84 boys and 98 girls) and low SES ladinos (136 boys and 101 girls) living in Guatemala City and very low SES Mayan Indians (139 boys and 73 girls) living in a rural town near the city. SES is used as a proxy for environmental quality. The coefficient of variation (CV) for distance achieved at each age, or for the increment of growth from age to age, is used as the measure of variability. The three samples differ significantly for variability in stature growth, both for the distance and the increments of growth. Low SES urban ladinos have the largest variability. Very low SES Mayan children have coefficients of variation that are sometimes equal to, and sometimes either larger or smaller than, CVs for the high SES ladinos. The results show that degree of environmental adversity does not correlate uniformly with growth variability. Factors such as rates of infant and early childhood mortality and the greater heterogeneity of the low SES urban environment, compared with the high SES urban or low SES rural environments, may account for differences in the CV in these three samples.

Childhood, adolescence, and longevity: A multilevel model of the evolution of reserve capacity in human life history

The grandmother hypothesis (GH) of Hawkes et al. ([1998]: Proc Natl Acad Sci USA 95: 1336–1339) finds that selection for lower adult mortality and greater longevity allow for the evolution of prolonged growth in human beings. In contrast, other researchers propose that the evolution of the human childhood and adolescent stages of life history prolonged the growth period and allowed for greater biological resilience and longevity compared with apes. In this article, the GH model is reanalyzed using new values for some of its key variables. The original GH set the age at human feeding independence at 2.8 years of age (weaning) and used demographic data from living foragers to estimate average adult lifespan after first birth at 32.9 years. The reanalysis of the GH uses age 7.0 years (end of the childhood stage) as the minimum for human feeding independence and uses data from healthier populations, rather than foragers, to derive an estimate of 48.9 years for average adult life span. Doing so finds that selection operated to first shorten the infancy stage (wean early compared with apes), then prolong the growth period, and finally result in greater longevity. The reanalysis provides a test of the reserve capacity hypothesis as part of a multilevel model of human life history evolution. Am. J. Hum. Biol. 2009.

Fatness biases the use of estimated leg length as an epidemiological marker for adults in the NHANES III sample

BACKGROUND We analyse the NHANES III sample to assess the suitability of measured stature and sitting height to estimate leg length (tibia + femur) and predict fatness. High rates of overweight in the United States population may lead to greater gluteo-femoral fat mass which will increase sitting height and artificially decrease estimates of both absolute and relative leg length. METHODS The analyses include 3076 women and 3233 men, 20.0-49.9 years of age of White, Black or Mexican-American ethnicity. The poverty index ratio, measured stature, sitting height, upper leg length, weight, four skinfolds, buttocks circumference and elbow, biacromial and biiliac breadths were extracted from the database. The sitting height ratio, % body fatness, % upper leg length (ULL/stature), and other indices were estimated. Correlation and principle component analysis were used to assess the relationship between measures of body fatness, relative leg length and the other variables. RESULTS For adults in the NHANES III % body fat is more strongly correlated with buttocks circumference (r = 0.87 and 0.78 for women and men), than with any measure of estimated leg length (rs range from -0.28 to -0.10 for both sexes). Principle components analysis separates fatness, stature and estimated leg length into uncorrelated factors for this sample. CONCLUSION Reports of a negative association between leg length and fatness for adults of the NHANES III are likely spurious, due to greater gluteo-femoral fat thickness increasing sitting height. Future rounds of the NHANES, and similar surveys in other nations with high body fat populations, should measure lower extremity length directly to better assess its relationship to health and disease risk.

Economic and Anthropological Assessments of the Health of Children in Maya Immigrant Families in the US

Immigration from developing countries to the US generally increases access to health care and clean water, but it also introduces some unhealthy lifestyle patterns, such as diets dense in energy and little regular physical activity. We present a transdisciplinary model of child health and examine the impact of immigration on the physical growth and health of Maya children in Guatemala and the US. Maya-American children are much taller and have longer legs, on average, than their counterparts in Guatemala. This suggests that immigration to the US improves their health. However, the Maya-American children also are much heavier than both Guatemalan Maya and White American children, and have high rates of overweight and obesity. Quantile regression analysis indicates that Maya are shorter except in the upper tail of the stature distribution, and have higher Body Mass Index (BMI) in the tails, but not in the middle of the BMI distribution. Leisure time spent in front of a television or computer monitor tends to raise BMI in the middle and lower tail of the distribution, but not in the upper tail.