Biological Anthropology Essay

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The closest mammalian relatives of the human species are the apes (chimpanzee, gorilla, orangutan, and gibbon), monkeys (the catarrhine cercopithecoids in the Old World, and platyrrhines in the Americas), and prosimians. Together these form the Order of Primates. Biological anthropology is the study of the biology of human and other primate species from an evolutionary and comparative perspective. It is concerned with the nature of the evolutionary process and with modes of adaptation to the environment. In continental Europe, the field of anthropology has been identified broadly with biological science, as distinct from ethnography, since the founding of the Société d’Anthropologie in Paris in 1859 by Paul Broca (Barnicot in Harrison et al. 1964) and of the journal Archiv für Anthropologie in Göttingen in 1861 by von Baer (Schwidetzky 1992). In the anglophone world, the term anthropology is sometimes used exclusively to denote social or cultural anthropology, although by etymology it embraces both fields.

Biological anthropology comprises five general subdisciplines: human evolution, primatology, human genetics, the study of human physical growth, and human ecology. The first two subdisciplines have sometimes been termed ‘physical anthropology’ in contrast to the second three as ‘human biology’; ‘biological anthropology’ embraces both. The field has been grounded in the natural sciences and medicine rather than social studies, which on their own have been thought not to provide the requisite biological competence (Harrison et al. 1964). Despite numerous assertions of the need to integrate these various subdisciplines with archaeology, social anthropology and associated social science fields, in practice few have succeeded in this aim since Franz Boas.

Human Evolution

Evolutionary studies in biological anthropology have focused on establishing the taxonomic (classificatory) and phylogenetic (evolutionary) relationships between fossil and living primates. In theory, phylogeny provides the necessary basis for taxonomy; but in practice, preliminary phylogenies can permit taxonomy to proceed. The method of cladistic taxonomy, which has become widely used, proceeds by first demonstrating primitive and derived characteristics of the members of a group, and then determining the derived characteristics shared among them (Groves 1989). The term hominid refers to populations and species with which humankind shares an evolutionary history excluding any other living primate. The hominid lineage is thought to have evolved between 5 and 10 million years ago. Studies of hominid evolution have attempted to explain where, how and why the human species evolved, hence a longstanding preoccupation with relationships between fossil hominids and their only surviving subspecies Homo sapiens sapiens (Foley 1987). However, the co-existence in the fossil record of species of Australopithecus and Homo indicates that the study of hominid origins is not to be equated with that of human origins (Lewin 1993).

These studies have an historical basis in the comparative anatomy which flourished in the eighteenth century. Their development was greatly influenced by the nineteenth-century works of Charles Darwin and T.H. Huxley which sought to take the study of humankind away from theology and bring it within the scope of natural history. Their more distant intellectual origins are sometimes sought in the works of Aristotle.

The advent of statistical techniques introduced by Quetelet, Galton and Pearson in the late nineteenth and early twentieth centuries enabled biometric approaches to become sophisticated (Boas 1938 [1911]; Barnicot in Harrison et al. 1964; Aiello 1992). A major problem has been separating the anatomical variation characteristic within a species from that expected between species. The use of functional anatomy and environmental physiology, and of comparison between the fossil record and field studies of extant primates in their social and environmental context, has allowed questions such as ‘Why are humans bipedal? Why hairless? Why human?’ to be asked and in some respects answered. Several competing phylogenies have been proposed and remain controversial.

In the 1970s, approaches from evolutionary ecology stressed the importance of understanding the ecological context in which evolutionary developments occurred. This has underpinned approaches to quantifying the costs and benefits of alternative evolutionary strategies. These strategies can be framed in terms of ‘r’ and ‘K’ selection models. The term ‘r’ refers to selection for high reproductive turnover associated with small body size and relatively immature (altricial) state at birth. ‘K’ refers to selection for a low reproductive rate according to the limits of the ‘carrying capacity’ of the ecological niche; and is associated with relatively advanced (precocial) developmental state at birth (Pianka 1988). Humans show some characteristics of both; and primates in general bear precocial offspring (Foley 1987).

For a large-bodied primate, the human shows a relatively large brain and a long period of childhood dependence. Various theories of nutritional constraints on the origins of these properties have been proposed. Some physical properties may take their form and size purely as a function of body weight. Allometry is a method of comparing animals by scaling features according to body size, and has therefore been an important tool in the analysis of primate relationships. It has been used to argue the central importance of energetic constraints on brain development in determining peculiarly human characteristics (Martin 1983).

The origins of the hominid adaptation of parental provisioning of offspring, extended dependency during childhood and large body size, have been sought in meat-eating, hunting or scavenging, and tool use. Studies of dental development suggest that an extended childhood was not present in the Australopithecines or Paranthropines. However, the nature and extent of meat acquisition and consumption in hominid evolution is a matter of controversy (Ulijaszek and Strickland 1993).

The human species has often been distinguished from others on the grounds of language, which is itself construed to be essential to ‘culture’ as a non-biological trait. Theories of the evolution of language are therefore of great importance. It has been argued that language origins lie in cognitive abilities rather than in properties of non-verbal communication (gesture/ call) which are shared by all primates (Burling 1993). However, there may also be advantages of social lubrication which are afforded by grooming behavior in non-human primates. These advantages may be more efficiently achieved by linguistic means in the human, therefore supporting larger social groups (Aiello and Dunbar 1993).

Primatology

Much of humankind’s evolution has taken place in the Tropics. Most contemporary non-human primates inhabit tropical or subtropical climates, although they have not always done so. The skeletal structure, body size, social behavior and ecology of non-human primates vary considerably across species; and within species there is behavioral variation across ecological zones. Almost all primates are intensely social. Field studies have concerned the social structure and behavior of primate groups, the biological and social control of reproduction, foraging patterns, and the relationships between these components of primate social systems. These studies comprise primate sociobiology; and in that one aim is to explain the evolution of such diversity, it contributes to the broader study of human evolution.

Behavioral studies of primates have used methods of animal ethology. These can give four kinds of explanation for why certain behavioral patterns exist: proximate causes, lying in immediate motivation or physiological processes; ontogenetic causes, which attribute cause to lifetime experiences during development; functional explanations, which attribute causality to the purpose of the behavioral pattern; and evolutionary explanations, which indicate the sequence of behavioral changes leading to the evolution of the pattern in question. These levels of explanation may interact. Thus all four types of explanation are needed if behavioral patterns are to be explained as part of an integrated biological system (Dunbar 1988). These types of explanation have tended to treat food and its distribution, the avoidance of predators, and the need to locate mates, as primary determinants of species biology including morphology and life-history patterns. Some have preferred to think of primates in terms of their ecology and behavior as adaptations which themselves result in morphological characteristics (Harrison et al. 1988).

Application of these methods and concepts to human populations comprises human sociobiology, which can be defined as the systematic study of the biological basis of human social behavior. Early attempts to develop this approach attributed to patterns of human social or cultural diversity a presumptive genetic basis (Durham 1991). This has been controversial among social anthropologists, and in its crudest form this approach is reminiscent of correlations between racial, cultural and mental variation which were postulated in the decades preceding World War II. These were examined critically by Franz Boas (1938 [1911]). However, the development of theories of the coevolution of biological and cultural characteristics, acknowledging the ways in which they may interact, has been fruitful in the study of diverse marriage patterns, colour terminology, analysis of incest prohibitions, patterns of milk use, and cannibalism (Durham 1991). Apparent conflicts between approaches taken in non-human primate studies and the concerns of sociocultural anthropology are reconcilable, argues Strier (2003), by exploring variation within non-human primate populations.

Human Genetics

The Darwinian theory of evolution by natural selection has been central to the development of biological anthropology. Early workers tended to explain human diversity in terms of migrations and intermixtures. Mendelian (particulate) inheritance of some features was postulated by showing that the variability of quantitative characters in groups of mixed parentage was greater than that of each parental group (Boas 1938 [1911]). It was not until immunological and biochemical methods enabled identification of blood groups, abnormal haemoglobin variants, and enzyme polymorphisms that particulate inheritance of such specific traits could be demonstrated (Barnicot, in Harrison et al. 1964). The ‘molecular revolution’ of the 1980s enabled even more sophisticated analysis of how trait inheritance via DNA research (O’Rourke 2003). The study of genetic variation within and between human populations, and that of processes of natural selection through effects of isolation, migration and differential reproductive success, have become well established. For example, the changing prevalence of non-insulin-dependent diabetes in Polynesians has been attributed to the effects of selection against a genotype which, under less affluent conditions, would have had energy-conserving advantages.

A fundamental question has been the degree of interaction between genetic and environmental sources of human biological variation. This has been investigated for many characteristics, including stature, obesity, the milk-sugar digesting enzyme lactase, types of muscle fiber, and IQ. However, the method of comparing identical twins reared together with those reared apart does not adequately separate variation due to genetic inheritance from that attributable to non-genetic inheritance, and tends to overestimate the genetic contribution. Other statistical methods attempt to overcome this problem (Shephard 1988). At the subcellular level, the conventional distinction between genetic and environmental sources of phenotypic variation is hard to maintain. There is a growing literature on the ways in which nutrients and genes interact to influence gene expression.

The ability to identify individuals by their genetic profiles is useful in forensic investigations. The subdiscipline of forensic anthropology has used a variety of methods of DNA fingerprinting. It has therefore had an important role in public practice, and enabled the determining of relationships between ethnic groups. Mitochondrial DNA is inherited through the maternal line and comparison across populations suggests their degree of genetic relatedness. On this basis, relationships between genetic and linguistic classifications of human groups have been examined. The method has also been used to argue that Homo sapiens sapiens originated in Africa rather than in different regions of the world.

In many societies, marriage between close consanguineous relatives is expected to occur, for example between first cousins or between uncle and niece. This has raised questions about the genetic consequences of such marriage patterns and their implications for health. Some studies have reported a high incidence of congenital malformations and post-natal mortality in the offspring of such unions in South Indian groups. Such marriage patterns may be linked to social controls over property and its inheritance. Studies have also been made of assortative mating for social economic or anthropometric characteristics, and of the relationship between such traits and reproductive success. These illustrate ways in which biological and social anthropological interests can converge: namely in studies of how social stratification may work as a vehicle for processes of natural selection in human groups.

Auxology

Auxology is the study of growth and development. The classical interest of biological anthropologists in the comparative anatomy of human groups is represented in many respects by contemporary anthropometric studies. Growth performance in children is a sensitive index of influences of infectious or congenital disease, nutrition, levels of physical activity, and to some degree mental development. As such, the measurement of growth in height, weight and body composition has been an important means of rating the general physical well-being of populations. Growth performance has been known to mirror social economic inequalities since the mid-nineteenth century (Tanner 1988), and has therefore become a means of identifying vulnerable groups, and of monitoring and evaluating the physical correlates of welfare policies.

The development of growth references as yardsticks for measuring growth performance has relied primarily on longitudinal or semilongitudinal studies over extended periods. These have been made on ostensibly healthy Caucasian children resident in Europe or North America and have been recommended by the World Health Organization for general use. It has been argued that differences in linear growth performance between reference populations and healthy, well-off study populations tend to be small compared to differences between rich and poor groups within a given study population. If this were true, then there would be a strong case for using a single universal growth reference. However, patterns of growth in height and weight during childhood in healthy study populations do not seem to follow a constant relationship to reference patterns. It has therefore also been argued that there are ethnic differences in genetic growth potential, or in growth pattern appropriate to the local ecology, which may justify the development and use of locally specific references. Universal references may be valuable as a yardstick for the general comparison of groups, locally specific references for the screening of individuals for a particular purpose.

Linear growth is closely associated with rate of maturation, which is in turn related to changes in body composition (relative fatness) and differs according to sex. The nature of this relationship can only be investigated fully in longitudinal studies, such as that conducted at the Fels Institute in America since 1929. Populations in which children show low stature at any given age tend also to be slow to mature and to reach puberty comparatively late. High median ages at menarche of over 18 years have been recorded in Papua New Guinea. However there is no simple relationship between growth performance, reproductive function, and the demographic structure and dynamics of populations. It has been speculated that body fatness itself influences reproductive function, and therefore provides a link between energy balance and reproductive performance. However, this is probably related to one of various stressors of which the effects are mediated by endocrinological mechanisms which are poorly understood (Mascie-Taylor and Lasker 1991).

Human Ecology

Ecology is the study of the interaction between organisms and their environment. Human ecology in general studies the adaptations which human groups make to their environment (see also ecological anthropology). Contemporary studies expand the concept of ‘ecology’, engaging fruitfully with a broad array ecology’s social dimensions (Leslie and Little 2003). This approach includes studies of the epidemiology of infectious disease, patterns of nutrition, reproductive function, demography, human exploitation of and impact on natural resources, and the implications which these various factors may have for each other and for practical policy.

Different diseases affect different human and non-human populations, age groups and the sexes with varying duration, severity and consequences for health and survival. The subject of epidemiology investigates these patterns. Anthropological inquiries of this kind have addressed the historical significance of disease patterns in human populations (Fenner 1980). Some have examined their interaction with household structure, living density and nutritional status. Assessment of the nutrition of human groups is an important practical issue. The validity of applying a single universal set of physical measures, for example those derived from healthy Western children, to all populations regardless of ethnic background, remains a matter of debate.

Factors influencing human reproductive function include level of physical exercise, dietary pattern, age, emotional stress, and other factors which act through endocrinological mechanisms. These factors show that human fertility is susceptible to regulation through several biological and social means, and that it is possible to understand some of the observed variation in fertility behavior in these terms (Mascie-Taylor and Lasker 1991). These investigations therefore contribute to the understanding of demography, the study of population structure and dynamics.

Human interactions with the environment have often been investigated using methods of energy flow analysis. This method became prominent in the early 1970s, after sharp increases in the price of fossil fuels raised public awareness of limits to energy resources. Studies by zoologists, anthropologists, geographers and others attempted to quantify the magnitude of energy inputs to, and outputs from, systems of food acquisition. Quantification of energy flows allows analysis of monetary and non-monetary subsistence patterns, and therefore the comparison of different systems by criteria of energetic efficiency. Ranking societies by these criteria allows analysis of broader relationships between human health and civilization (Boyden 1987). Some such studies have been criticized for methodological deficiencies, reductionism, sociological naivety, lack of attention to the household rather than the whole community, and failure to consider seasonal variation. Nevertheless, quantification of energy flows remains an important tool in the analysis of the biology of human subsistence patterns.

Across all categories of biological anthropology, epistemological shifts in anthropology as a whole have begun to spur debate, with regard to both theoretical assumptions and ethical practice. Consciousness of the impact of research on subjects has come to the fore, in relation to nonhuman primates, human remains, and living populations (Turner 2005). While repatriation is one well-explored ethical domain, the ethically questionable practice of ‘owning’ genetic material is also especially contested (Marks 2002b). However, the putative ‘holism’ of anthropology has come under serious threat as biological anthropology has contended with these epistemological shifts. Although the existence of a past Boasian holism is arguable (Borofsky 2002), more pertinently even superficial institutional holism was at risk as several high-profile departments in the United States fractured along cultural and biological lines in the late twentieth and early twenty-first century. Recognizing biological anthropologists’ sense of marginalization within the discipline as a whole, some have called for a greater engagement of biological anthropologists with professional organizations, and increased efforts to communicate the relevance of biological anthropological to central concerns of the discipline, for example, race, reproduction, gender, violence, language, cognition, technology and death (Calcagno 2003). The ability of biological anthropology to negotiate fraught domains of ethics and relevance will be critical not just for the subfield, but for anthropology’s broader claims of disciplinary holism.

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