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.     

What makes us human? Answers from evolutionary anthropology

Today, scholars from numerous and highly diverse fields are not only addressing the question of what makes us human, but also seeking input from other disciplines to inform their answers to this fundamental issue. However, for the most part, evolutionary anthropologists are not particularly prominent in this discussion, or at least not acknowledged to be. Why is this the case? One reason may be that although evolutionary anthropologists are uniquely positioned to provide valuable insight on this subject, the responses from any one of us are likely to be as different as the research specializations and intellectual experiences that we bring to the table. Indeed, one would anticipate that a paleoanthropologist would not only have different views than a primatologist, geneticist, or behavioral ecologist, but from other paleoanthropologists as well. Yet if asked by a theologian, psychologist, or political scientist, and perhaps most importantly, by any curious person outside the walls of academia, do we have a response that most evolutionary anthropologists could agree on as reflecting our contributions to the understanding of being and becoming human? Our introductory textbooks usually begin with this fundamental question, yet seldom produce a concise answer. © 2012 Wiley Periodicals, Inc.     

The Importance of Population Growth and Regulation in Human Life History Evolution

Explaining the evolution of human life history traits remains an important challenge for evolutionary anthropologists. Progress is hindered by a poor appreciation of how demographic factors affect the action of natural selection. I review life history theory showing that the quantity maximized by selection depends on whether and how population growth is regulated. I show that the common use of R, a strategy’s expected lifetime number of offspring, as a fitness maximand is only appropriate under a strict set of conditions, which are apparently unappreciated by anthropologists. To concretely show how demography-free life history theory can lead to errors, I reanalyze an influential model of human life history evolution, which investigated the coevolution of a long lifespan and late age of maturity. I show that the model’s conclusions do not hold under simple changes to the implicitly assumed mechanism of density dependence, even when stated assumptions remain unchanged. This analysis suggests that progress in human life history theory requires better understanding of the demography of our ancestors.     

There is an obstetrical dilemma: Misconceptions about the evolution of human childbirth and pelvic form

Compared to other primates, modern humans face high rates of maternal and neonatal morbidity and mortality during childbirth. Since the early 20th century, this “difficulty” of human parturition has prompted numerous evolutionary explanations, typically assuming antagonistic selective forces acting on maternal and fetal traits, which has been termed the “obstetrical dilemma.” Recently, there has been a growing tendency among some anthropologists to question the difficulty of human childbirth and its evolutionary origin in an antagonistic selective regime. Partly, this stems from the motivation to combat increasing pathologization and overmedicalization of childbirth in industrialized countries. Some authors have argued that there is no obstetrical dilemma at all, and that the difficulty of childbirth mainly results from modern lifestyles and inappropriate and patriarchal obstetric practices. The failure of some studies to identify biomechanical and metabolic constraints on pelvic dimensions is sometimes interpreted as empirical support for discarding an obstetrical dilemma. Here we explain why these points are important but do not invalidate evolutionary explanations of human childbirth. We present robust empirical evidence and solid evolutionary theory supporting an obstetrical dilemma, yet one that is much more complex than originally conceived in the 20th century. We argue that evolutionary research does not hinder appropriate midwifery and obstetric care, nor does it promote negative views of female bodies. Understanding the evolutionary entanglement of biological and sociocultural factors underlying human childbirth can help us to understand individual variation in the risk factors of obstructed labor, and thus can contribute to more individualized maternal care.     

Resolving the Anti-Antievolutionism Dilemma: A Brief for Relational Evolutionary Thinking in Anthropology

ABSTRACT   Anthropologists often disagree about whether, or in what ways, anthropology is "evolutionary." Anthropologists defending accounts of primate or human biological development and evolution that conflict with mainstream "neo-Darwinian" thinking have sometimes been called "creationists" or have been accused of being "antiscience." As a result, many cultural anthropologists struggle with an "anti-antievolutionism" dilemma: they are more comfortable opposing the critics of evolutionary biology, broadly conceived, than they are defending mainstream evolutionary views with which they disagree. Evolutionary theory, however, comes in many forms. Relational evolutionary approaches such as Developmental Systems Theory, niche construction, and autopoiesis–natural drift augment mainstream evolutionary thinking in ways that should prove attractive to many anthropologists who wish to affirm evolution but are dissatisfied with current "neo-Darwinian" hegemony. Relational evolutionary thinking moves evolutionary discussion away from reductionism and sterile nature–nurture debates and promises to enable fresh approaches to a range of problems across the subfields of anthropology. [Keywords: evolutionary anthropology, Developmental Systems Theory, niche construction, autopoeisis, natural drift]     

The effects of residential ecology on patterns of child work and mother's reproductive success among Indo-Fijians

A central question in human life history theory surrounds the rapid pace of reproduction of human mothers. Accordingly, evolutionary anthropologists have debated who provides assistance to human mothers and how. Here, we develop an embodied capital framework (i.e., a parental investment strategy focused on improving the adult productivity of offspring) to understand urban–rural differences in the extent to which children help to underwrite the costs of their dependence among Indo-Fijians. We employ multiple regression analysis to explore the relationships among various categories of helpful activity, residential ecology and mother's reproductive success and show that, while rural children work more overall compared to urban children, childcare is the only productive activity with any relationship to mother's reproductive success. We conclude by providing support for the general idea that children are potentially important sources of allomaternal help, but emphasize the need for more nuanced models of how such help is provided.     

Grandmother hypothesis and primate life histories

The adaptive significance of midlife menopause in human females has long engaged the attention of evolutionary anthropologists. In spite of extensive debate, the problem has only recently been examined in the context of primate life histories. Here I extend those investigations by comparing life history traits in 16 primate species to test predictions generated from life history theory. In humans, late ages of maturity and higher than expected birth rates are systematically associated with extended postmenopausal longevity. Links among these adjustments on the primate pattern can explain how selection could slow somatic senescence without favoring extension of the fertile span. This conclusion is consistent with the observation that our fertile spans are similar to those of other pongids. The shape of the argument herein demonstrates the utility of life history theory for solving problems of adaptive evolution in female life history traits, with consequences for broader arguments regarding human evolution.     

Cooperation and the evolution of intelligence

The high levels of intelligence seen in humans, other primates, certain cetaceans and birds remain a major puzzle for evolutionary biologists, anthropologists and psychologists. It has long been held that social interactions provide the selection pressures necessary for the evolution of advanced cognitive abilities (the 'social intelligence hypothesis'), and in recent years decision-making in the context of cooperative social interactions has been conjectured to be of particular importance. Here we use an artificial neural network model to show that selection for efficient decision-making in cooperative dilemmas can give rise to selection pressures for greater cognitive abilities, and that intelligent strategies can themselves select for greater intelligence, leading to a Machiavellian arms race. Our results provide mechanistic support for the social intelligence hypothesis, highlight the potential importance of cooperative behaviour in the evolution of intelligence and may help us to explain the distribution of cooperation with intelligence across taxa.     

The concepts of asymmetric and symmetric power can help resolve the puzzle of altruistic and cooperative behaviour

Evolutionary theory predicts competition in nature yet altruistic and cooperative behaviour appears to reduce the ability to compete in order to help others compete better. This evolutionary puzzle is usually explained by kin selection where close relatives perform altruistic and cooperative acts to help each other and by reciprocity theory (i.e. direct, indirect and generalized reciprocity) among non‐kin. Here, it is proposed that the concepts of asymmetry and symmetry in power and dominance are critical if we are ever to resolve the puzzle of altruism and cooperation towards non‐kin. Asymmetry in power and dominance is likely to emerge under competition in nature as individuals strive to gain greater access to the scarce resources needed to survive and reproduce successfully. Yet asymmetric power presents serious problems for reciprocity theory in that a dominant individual faces a temptation to cheat in interactions with subordinates that is likely to far outweigh any individual selective benefits gained through reciprocal mechanisms. Furthermore, action taken by subordinates to deter non‐reciprocation by dominants is likely to prove prohibitively costly to their fitness, making successful enforcement of reciprocal mechanisms unlikely. It is also argued here that many apparently puzzling forms of cooperation observed in nature (e.g. cooperative breeding in which unrelated subordinates help dominants to breed) might be best explained by asymmetry in power and dominance. Once it is recognized that individuals in these cooperative interactions are subject to the constraints and opportunities imposed on them by asymmetric power then they can be seen as pursuing a ‘least bad’ strategy to promote individual fitness – one that is nevertheless consistent with evolutionary theory. The concept of symmetric power also provides important insights. It can inhibit reciprocal mechanisms in the sense that symmetric power makes it easier for a cheat to appropriate common resources while incurring fewer penalties. Nevertheless under certain restrictive conditions, symmetric power is seen as likely to promote direct reciprocity through ‘tit for tat’.     

The adaptive nature of culture

Some have argued that the major contribution of anthropology to science is the concept of culture. Until very recently, however, evolutionary anthropologists have largely ignored culture as a topic of study. This is perhaps because of the strange bedfellows they would have to maintain. Historically, anthropologists who claimed the focus of cultural anthropology tended to be anti‐science, anti‐biology, or both. Paradoxically, a segment of current mainstream cultural anthropology has more or less abandoned culture as a topic. It is particularly ironic that in spite of a growing awareness among evolutionary anthropologists that culture is critical for understanding the human condition, the topic of culture has fallen out of favor among many “cultural” anthropologists. ^1,2     

Evolutionary psychology and the generation of culture,part I: Theoretical considerations

Culture is the ongoing product of the evolved psyches of individual humans living in groups. Progress in our understanding of culture as a phenomenon depends on progress in uncovering the nature of the evolved mechanisms that comprise the human psyche, including but not limited to those responsible for learning. Actual attemps to specify information processing mechanisms that could, in fact, perform tasks humans routinely perform have demonstrated that the human psyche cannot, even in principle, be comprised only of a general purpose learning mechanism or any other general purpose mechanism, such as an inclusive fitness maximizer. Instead, the human psyche appears to consist of a large number of mechanisms, many or most of which are special purpose and domain-specific. The output of these mechanisms taken together constitutes the “private culture” of each individual, and the interactions of these private cultures lead to the cross-individual patterns of similarity that have led anthropologists to think typologically of social groups as having “a” culture. The construction of a scientific theory of culture requires as its building blocks specific models of these psychological mechanisms, and so evolutionary anthropology depends on the forging of an evolutionary psychology. The most productive application of evolutionary biology is, therefore, in the study of the psychological mechanisms that generate and shape culture, rather than in the attempt to impose on cultural change too close a parallel to population genetics and organic evolution.     

Evolutionary Contributions to Solving the ��Matrilineal Puzzle��

Matriliny has long been debated by anthropologists positing either its primitive or its puzzling nature. More recently, evolutionary anthropologists have attempted to recast matriliny as an adaptive solution to modern social and ecological environments, tying together much of what was known to be associated with matriliny. This paper briefly reviews the major anthropological currents in studies of matriliny and discusses the contribution of evolutionary anthropology to this body of literature. It discusses the utility of an evolutionary framework in the context of the first independent test of Holden et al.'s 2003 model of matriliny as daughter-biased investment. It finds that historical daughter-biased transmission of land among the Mosuo is consistent with the model, whereas current income transmission is not. In both cases, resources had equivalent impacts on male and female reproduction, a result which predicts daughter-biased resource transmission given any nonzero level of paternity uncertainty. However, whereas land was transmitted traditionally to daughters, income today is invested in both sexes. Possible reasons for this discrepancy are discussed.     

Sexual dimorphism in the human post-reproductive life-span: Possible causes

The fact that human females exhibit a post-reproductive life-span (menopause) and males do not is considered in evolutionary perspective. Two possible non-adaptive (incidental) explanations are discussed and rejected on available evidence. This sex difference is then considered as a possible adaptive response to differential parental investment tendencies of the two sexes. This hypothesis is evaluated in the context of sexual selection theory and the pattern of other observed sex differences in Homo sapiens. Finally, an attempt is made to explain the emergence of contemporary human investment patterns in terms of the changing patterns of parental certainty brought about by the Neolithic revolution. Cross-cultural data on investment patterns by subsistence type are used to test this hypothesis.     

Cryptic Evolution: Does Environmental Deterioration Have a Genetic Basis?

Cryptic evolution has been defined as adaptive evolutionary change being masked by concurrent environmental change. Empirical studies of cryptic evolution have usually invoked a changing climate and/or increasing population density as the form of detrimental environmental change experienced by a population undergoing cryptic evolution. However, Fisher (1958) emphasized that evolutionary change in itself is likely to be an important component of "environmental deterioration," a point restated by Cooke et al. (1990) in the context of intraspecific competition. In this form, environmental deterioration arises because a winning lineage has to compete against more winners in successive generations as the population evolves. This "evolutionary environmental deterioration" has different implications for the selection and evolution of traits influenced by resource competition than general environmental change. We reformulate Cooke's model as a quantitative genetic model to show that it is identical in form to more recent developments proposed by quantitative geneticists. This provides a statistical framework for discriminating between the alternative hypotheses of environmental change and environmental deterioration caused by evolutionary change. We also demonstrate that in systems where no phenotypic change has occurred, there are many reasonable biological processes that will generate patterns in predicted breeding values that are consistent with what has been interpreted as cryptic evolution, and care needs to be taken when interpreting these patterns. These processes include mutation, sib competition, and invisible fractions.     

The State of Biological Anthropology in 2008: Is Our Discipline Strong and Our Cause Just?

ABSTRACT   Biological anthropologists inform a largely professional discourse on the evolutionary history of our species. In addition, aspects of our biology, the ways in which we vary, and certain patterns of behavior are the subjects of a more public and popular conversation. The social contexts in which we work not only define our times but also produce the anthropologists that in turn construct an emergent understanding of our species' (and our societies') inner workings. In this review of scholarly production, I focus on developments within a selection of "sub-subdisciplines" that were particularly influential in bending the arc of biological anthropology in 2008, namely: evolutionary medical anthropology, anthropological neuroscience, forensic anthropology, primatology, and paleoanthropology. Ultimately, this review demonstrates, yet again, anthropology's great contribution: the ability to incorporate new technologies and research methodologies into a synthetic and integrative interdisciplinary approach toward the elucidation of human behavior, evolution, and biocultural engagements with the environment. [Keywords: biological anthropology, year in review, 2008, science and society]     

Biological anthropology of aging--past,present and future

Biological anthropologists have a strong tradition of studying growth and development and research on aging has been limited. This paper explores the past and current contribution of biological anthropologists to the field of aging through an examination of the American Journal of Physical Anthropology (AJPA) and the American Journal of Human Biology (AJHB). It is clear from this survey that biological anthropologists and human biologists have predominantly studied growth and developmental processes relative to aging. However, there is a trend of increasing interest in aging over time. In the AJHB, papers discussing chronic disease were predominant, followed by reproductive aging (19%), bone aging (15%) and body composition (10%). Within the AJPA, the majority of articles were in the field of human biology (43%) and bioarchaelogy (42%) with a lesser contribution from primatology (14%) and dermatogliphics (1%). Biological anthropologists still have great potential to make contributions to gerontology with our evolutionary and holistic perspectives and focus on cross-cultural research.     

Symmetric competition as a general model for single-species adaptive dynamics

Adaptive dynamics is a widely used framework for modeling long-term evolution of continuous phenotypes. It is based on invasion fitness functions, which determine selection gradients and the canonical equation of adaptive dynamics. Even though the derivation of the adaptive dynamics from a given invasion fitness function is general and model-independent, the derivation of the invasion fitness function itself requires specification of an underlying ecological model. Therefore, evolutionary insights gained from adaptive dynamics models are generally model-dependent. Logistic models for symmetric, frequency-dependent competition are widely used in this context. Such models have the property that the selection gradients derived from them are gradients of scalar functions, which reflects a certain gradient property of the corresponding invasion fitness function. We show that any adaptive dynamics model that is based on an invasion fitness functions with this gradient property can be transformed into a generalized symmetric competition model. This provides a precise delineation of the generality of results derived from competition models. Roughly speaking, to understand the adaptive dynamics of the class of models satisfying a certain gradient condition, one only needs a complete understanding of the adaptive dynamics of symmetric, frequency-dependent competition. We show how this result can be applied to number of basic issues in evolutionary theory.     

The psychology of primate cooperation and competition: a call for realigning research agendas

Cooperation and competition are two key components of social life. Current research agendas investigating the psychological underpinnings of competition and cooperation in non-human primates are misaligned. The majority of work on competition has been done in the context of theory of mind and deception, while work on cooperation has mostly focused on collaboration and helping. The current impression that theory of mind is not necessarily implicated in cooperative activities and that helping could not be an integral part of competition might therefore be rather misleading. Furthermore, theory of mind research has mainly focused on cognitive aspects like the type of stimuli controlling responses, the nature of representation and how those representations are acquired, while collaboration and helping have focused primarily on motivational aspects like prosociality, common goals and a sense of justice and other-regarding concerns. We present the current state of these two bodies of research paying special attention to how they have developed and diverged over the years. We propose potential directions to realign the research agendas to investigate the psychological underpinnings of cooperation and competition in primates and other animals.     

Monogamy,strongly bonded groups,and the evolution of human social structure

Human social evolution has most often been treated in a piecemeal fashion, with studies focusing on the evolution of specific components of human society such as pair‐bonding, cooperative hunting, male provisioning, grandmothering, cooperative breeding, food sharing, male competition, male violence, sexual coercion, territoriality, and between‐group conflicts. Evolutionary models about any one of those components are usually concerned with two categories of questions, one relating to the origins of the component and the other to its impact on the evolution of human cognition and social life. Remarkably few studies have been concerned with the evolution of the entity that integrates all components, the human social system itself. That social system has as its core feature human social structure, which I define here as the common denominator of all human societies in terms of group composition, mating system, residence patterns, and kinship structures. The paucity of information on the evolution of human social structure poses substantial problems because that information is useful, if not essential, to assess both the origins and impact of any particular aspect of human society.     

New phylogenetic information suggests both an increase and at least one loss of cooperative breeding during the evolutionary history of Aphelocoma jays

Efforts to identify ecological and life history factors associated with cooperative breeding have been largely unsuccessful, and interest is growing in the role of phylogenetic history in determining the distribution of this social system among lineages. In birds, cooperative breeding is distributed non-randomly among lineages, suggesting that phylogenetic inertia may play an important role in determining its distribution. The bird genus Aphelocoma has been particularly well studied because, although it is a relatively small genus, it shows broad among-lineage variation in level of cooperation. Previous analyses described an unusual unidirectional pattern of evolutionary loss of cooperation in Aphelocoma. Here, historical reconstructions based on new phylogenetic data suggest that evolutionary changes in cooperation have been bidirectional, with at least one gain and at least one loss over relatively recent timescales. This result emphasizes that, although history plays an important role in determining the incidence of cooperative breeding, cooperative behavior can switch relatively quickly in evolutionary time and may be influenced by the ecological context within which particular populations are distributed.