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Committee on Population; Division of Behavioral and Social Sciences and Education; National Research Council; Weinstein M, Lane MA, editors. Sociality, Hierarchy, Health: Comparative Biodemography: A Collection of Papers. Washington (DC): National Academies Press (US); 2014 Sep 22.

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Sociality, Hierarchy, Health: Comparative Biodemography: A Collection of Papers.

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1Sociality, Hierarchy, Health: Comparative Biodemography

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In the nearly 20 years since the first meetings that resulted in the publication of Between Zeus and the Salmon (National Research Council, 1997), biodemography as a discipline has flourished, generally proceeding in three complementary directions. Along one line, biosocial surveys have proliferated. Initiatives as diverse as the Health and Retirement Study1 and its offshoots; Midlife in the United States;2 the National Social Life, Health, and Aging Project;3 and the Taiwan biomarker study, Social Environment and Biomarkers of Aging Study4 have been providing social and demographic data that also incorporate a wide range of biomarkers. This line of research is explored in three National Research Council (NRC) volumes: Cells and Surveys (2001), Biosocial Surveys (2007), and Conducting Biosocial Surveys (2010).

In a second line of research, diverse studies of the biodemography of longevity have been thriving, with much of the work led by contributors to the 1997—as well as to this—volume: Steven Austad, James Carey, Caleb Finch, Hillard Kaplan, Ron Lee, James Vaupel, and Ken Wachter. The first paper in this volume, by Kenneth Wachter, is particularly helpful in looking back at a condensed history of biodemographic research on longevity and forward to much of the workshop. A third direction, on the biodemography of reproduction, was followed in Offspring, which was published by the National Academies Press in 2003 (National Research Council, 2003).

Development of this volume was prompted by the sense that it would be a good time to revisit both the theoretical underpinnings of biodemography and the empirical findings that have emerged over the past two decades. This introduction does not pretend to be a comprehensive summary of the contents of this volume; rather, it is an admittedly idiosyncratic tour through some of the key areas of inquiry, important workshop discussions, and intellectual foci of the individual papers.

The steering committee for the workshop that led to this volume was charged with commissioning papers that would examine cross-species comparisons of social environments with a focus on social behaviors along with social hierarchies and connections, to examine their effects on health, longevity, and life histories.

A large charge! The result is far ranging, covering a broad spectrum of human and nonhuman animals, exploring a variety of measures of position in social hierarchies and social networks, and drawing links among these factors to health outcomes and trajectories. The scope of biodemography—with apologies to T.S. Eliot5— has been substantially expanded beyond the mere birth, copulation, and death of a cannibal isle. Clearly, no single workshop or volume can cover everything related to comparative biodemography. This workshop did not address, for example, the kinds of genetic and social changes that have occurred over the last ten thousand years or so since people began living in settled communities, the effects on health of sedentary group life, or the genesis and increase in hierarchy in human societies.

Notably missing from among the papers in this volume is consideration of migration. Surely, migration is linked to social connection, given the large remittances that migrants often send to their natal home, and to hierarchy, given the variable social and economic niches that migrants occupy. The workshop touched on it indirectly in discussions of the movement of young male baboons away from their maternal groups, and in comments about swarming bees, but there was no thorough consideration of it.

Also missing is consideration of ape social systems, especially those of chimpanzees and bonobos, and their implications for health and longevity, a topic that is receiving increasing attention. Among chimpanzees, females migrate and males remain in natal territory, cortisol is positively correlated with rank in males but negatively correlated among females (Muller and Wrangham, 2004; Emery Thompson et al., 2010), and females mate with all or most adult males in their community during estrus (Emery Thompson, 2013). All of these characteristics unfold in ways that affect profiles of stress over the lifecourse, and sex and rank differences in morbidity and mortality. More generally, the workshop papers and discussions addressed only a limited number of species; it must be considered a start on comparative biodemography.

In addition to members of the original cast of Zeus mentioned above, the workshop was enriched by the contributions of biologists and anthropologists—as well as a few new demographers and epidemiologists—who brought new perspectives, data, and analysis to the fore: Chris Kuzawa and Dan T.A. Eisenberg, Anne Bronikowski and her colleagues, Steve Suomi, Michael Marmot and Robert Sapolsky, Paul Hooper and his colleagues, John Wingfield, Karen Ryan, Jenny Tung, Kenneth Weiss, Jonathan Stieglitz and his colleagues, Brian Johnson, Peter Ellison and Mary Ann Ottinger, Joan Silk, Susan Alberts and her colleagues, Janet Mann, John Haaga, David Miller, and Jeffrey Kahn. Papers from most of the presenters at the workshop are included in this volume, and video-recordings of the workshop talks by those authors and discussants who have agreed are available at UCTV Seminars.6


Intergenerational transfers were a recurring theme in the presentations, papers, and discussions (see, for example, papers in this volume by Hooper, Gurven, and Kaplan, by Lee, by Stieglitz and co-authors, and by Wachter). Mostly, intergenerational transfers are from older to younger generations. Genetic material is a fundamental form of downward intergenerational transfer; transfers of wealth taking the form of food or other resources figure prominently in life histories. A particularly interesting form of intergenerational transfer is position in social hierarchy—an inheritance that has a strong effect on health. As noted in presentations by Alberts and her coauthors, by Suomi and his collaborator, and by Silk, among both baboons and rhesus macaques, infants inherit their mothers' position in the social hierarchy. Generally speaking, as discussed in the presentation of Michael Marmot, among humans in industrialized settings, higher position in hierarchy is associated with better health and lower mortality. And, while less documented than in humans (see Finch and Singer), position in hierarchies among nonhuman primates is also directly related to health. If position in hierarchies is determined by parents' status, then changes in opportunities for upward mobility will affect the health of the inheritors. The extent to which social mobility has declined, or whether indeed it has declined, in industrialized nations has become a matter that is much discussed in the popular press, although the scholarly evidence appears to be mixed. But, if it is true that social mobility is declining, it has important consequences for improving the health of future generations and addressing social disparities in health.

The so-called “grandmother hypothesis” is part of an ongoing discussion about life history theory—the tradeoffs and relationships among reproduction, longevity, and senescence. Humans typically enjoy a long post-reproductive life, although this is rare among other species. The question is, why do women live past menopause? An important aspect of this post-reproductive life is the contribution made to their descendants by post-reproductive humans, mothers in particular. The grandmother hypotheses—there are various formulations—seek to attribute this post-reproductive period to improved survival of those descendants. The paper by Hooper and colleagues suggests an amendment to the grandmother hypothesis, with evidence of large flows of resources from older men to their adult children and to their grandchildren. The importance of grandfathers, and the role of men in general, has been underappreciated in models of human life history evolution, and in the health and well-being of three generations of individuals.

The paper by Ellison and Ottinger puts forward important insights drawn from comparative data. They argue that an incremental approach, as proposed, for example, by Chu and Lee (2013), is central to the explanation, but make an interesting case for an alternative evolutionary pathway. These authors suggest that post-reproductive survival has been lengthened rather than reproduction ending early; their conclusion is that “post-reproductive life selects for ‘grandmotherly’ behavior, not the other way around.” This issue was further discussed at the workshop. Given that there is significant intra-population variability in ages of last reproduction, menopause, and death, and in rates of aging, it is clear that natural selection is continually acting on aging in both reproductive and other organ systems. Thus, a fundamental question is why natural selection has favored similar rates of reproductive aging among humans and apes, but a much longer lifespan in humans. Another question is whether reproductive aging differs between chimpanzees and humans in the extent to which physical condition determines age of last reproduction, with, as suggested by Emery Thompson et al. (2010), the effect of physical condition being much stronger in chimpanzees.

Not all intergenerational transfers are downward, and as noted by Ellison and Ottinger, their proposed pathway allows for upward contributions from individuals who have not yet reached reproductive maturity, an opening for what they term “indirect reproductive effort.” Such upward transfers should be familiar, at least to demographers, from explanations of fertility transitions that posit that changes in the direction of intergenerational transfers contribute to declines in fertility. Even when net flows are downward across generations, day-to-day flows tend to go in both directions in small-scale human economies, revealing the importance of social integration to individual health and survival.

The paper by Lee focuses on his work on the role of intergenerational transfers in life history theory. Underlying his work is how consideration of intergenerational tradeoffs enhances the classical, typically intra-individual, understanding of allocations among growth, maintenance, survival, and reproduction. Using both simulation and analytic techniques, he develops a set of six hypotheses that form the basis of an ambitious empirical research agenda. One hypothesis—that the parent that is more involved in care or transfers to the child will live longer—is well supported by evidence among humans and baboons (see, for example, the paper by Alberts and her colleagues and discussion of it below). Another hypothesis, addressed by Ellison and Ottinger, is that post-reproductive life is associated with longer dependency of offspring. As noted below, documentation of extended post-reproductive life in the wild is sparse, but it will be enlightening to start looking at data that address this hypothesis and the others Lee proposes.

Like Lee, the paper by Hooper and his colleagues explores human life histories, providing a framework for understanding how links among ecology, sociality, and demographic characteristics provide insight into human evolutionary history. They propose three underlying social relationships that respond, and have responded to, human ecology and which have important effects on health: kin-based altruism, cooperative pair bonds, and reciprocal cooperation. They draw on data from ethnographic research to examine interdependencies among the kinds of factors explored by Lee (longevity, post-reproductive survival, and intergenerational transfers), parental coupling and investment, and cooperative social insurance. It was especially refreshing to see a discussion of the pros and cons of using data from currently existing hunter-gatherers or forager-horticulturalists to infer information about humans' evolutionary past. All too often, it seems, the assumption is made that such populations reflect our history: “… contemporary populations,” they remind us, “are not frozen relics of the past.”

Psychological well-being and mood disorders, a dimension of health that has not been widely considered by biodemographers, is examined in light of life histories by Stieglitz and his colleagues using data from adult Tsimane forager-farmers of Bolivia. They explore whether mood disorders have an adaptive value that is linked to the ability to produce and transfer resources that improve survival of oneself or one's kin. They propose that productivity has both a direct effect on well-being and an indirect effect that is mediated by transfers of resources.


The social gradient in health, that is, that expectation of life is directly associated with position in social hierarchies as measured, for example, by education or income, is widely observed in both contemporary societies, and—as far as the data will help determine—in historical populations (Marmot and Sapolsky, Finch and Singer), but individual health conditions show more variable relationships that depend on context. Using data from baboons, “… who don't smoke, eat fast foods, or have differential access to health care depending on ability to pay,” Marmot and Sapolsky speculate that low rank itself may not be the causal agent, rather, it may be that low rank is associated with lack of control over life circumstances, which in turn lead to stress and ultimately poor health. That is, what is observed as low rank may be a proxy for psychosocial stressors that are beyond the control of the person, or baboon, who experiences them.

There may be cross-species similarities among primates (including humans) in the role of stress in mediating the relationship between low status and poor health and mortality outcomes. At the same time, it is likely that the relationships among resources, social status, and health will vary across human societies depending upon numerous factors. Whether access to food energy is a constraint on health is one example: the relationship between socioeconomic status and obesity varies by sex, ethnicity, race, and country, and those factors interact in complex ways.

The understanding that mind and body are intimately linked has a venerable history: “The body's mischiefs, as Plato proves, proceed from the soul: and if the mind be not first satisfied, the body can never be cured.”7 The paper by Karen Ryan focuses, in particular, on mechanisms that link chronic exposure to stress with metabolic disease and health. One such mechanism is stress-induced chronic activation of the immune system, which appears to play an important role in the development of metabolic diseases such as obesity, cardiovascular disease, and Type-2 diabetes. As described by Ryan, a recent area of research elaborates the relationships among inflammation, the microbiome, and health. One hypothesis of interest is that psychosocial stress causes changes in gut microbiota, which in turn stimulates the immune system, ultimately leading to chronic metabolic disease.

Evidence from biosocial surveys is mixed. Links between self-reported stress (both perceived stress and stressors) and measures of overall physiological dysregulation were weak in work reported by Glei, Goldman, and their colleagues (Glei et al., 2007). In support of Ryan's hypothesis, however, there is some evidence of an association between exposure to stressors and inflammation (Glei et al., 2013a). Comparative work also suggests that perceived stress is associated with cardiovascular and metabolic markers and inflammation, at least in some populations (Glei et al., 2013b).


E.M. Forster exhorts, “Only connect!”8 For both human and nonhuman animals, connection matters. The importance of social connections reverberated throughout the workshop and appears throughout this volume. The paper by Joan Silk provides an excellent example of the effects of social relationships. The work of Silk and her colleagues, first among the Amboseli baboons and later elaborated observing the Moremi baboons, shows strong evidence of stable social bonds, with grooming partners generally drawn from close kin, but existing even among females that had no close relatives. The connections had important consequences for health: females with strong social connections had greater longevity and better infant survival than those with weaker connections. Position in hierarchy had no effect on infant survival although higher position was associated with greater longevity.

A comparison of the chapters that focus on social relationships among baboons with those on humans reveals an important difference. Social support is critical in the lives of both species, but among baboons, most support is utilized in competitive relationships with other group members; that is, social support in baboons appears to be largely a zero sum game with clear winners and losers. It has been proposed (e.g., Alexander 1974) that predation risk motivates grouping in primates, and the complex social relationships that result help manage the competition generated by group life. In contrast, among humans, social support and transfers of resources generate positive surpluses by buffering risk, providing help in times of illness, increasing resource production through cooperation, accruing gains from a division of labor by age and sex, and creating intergenerational assistance in human capital formation. Of course, competition and status striving is a feature of human social relationships that parallel those of baboons.

The importance of social connection for human health was dramatically illustrated by Finch and Singer. They presented work by Singer and Ryff (1999) and Ryff et al. (2001), who used data from the Wisconsin Longitudinal Study.9 Both men and women who had positive relationship pathways, that is, who had at least one very caring parent when they were growing up and who had a good relationship during adulthood, had lower health risk profiles than those on negative pathways. What is especially striking about the relationship pathways is how much they moderate the effects of disadvantageous economic conditions. Among people who had negative economic pathways (either persistently poor or declining), those who also had negative relationships were two or three times as likely to have high health risk indexes as those with positive relationships. More generally, variability in a health risk index was lower among study participants who had positive relationships than among the participants who had negative relationships. Finch and Singer conclude that “with positive relationships across life, health is less dependent on money.” Perhaps this finding offers some hope if indeed society is facing dwindling levels of social mobility: “Only connect!”


A central challenge for biodemographers is elegantly stated in the paper by Tung: “Biodemographers are fundamentally interested in real populations—in which individual genetic effects will generally be modest, and individual study subjects will be genetically diverse.” As noted by Wachter, “the scientific returns from biodemographers doing the same kinds of studies that biomedical and genetic researchers are already doing seem modest.” What then, can biodemographers contribute? There was considerable debate on this question during the workshop. One promising area is the kind of work being done by Wachter in stochastic vitality models and in non-linear mutation accumulation. The extent to which model calibration can be achieved using the kinds of genome-wide data that are becoming increasingly available remains to be seen. Wachter appears to be cautiously optimistic.

The mathematical work by Wachter and his colleagues relaxes some of the more restrictive assumptions of earlier models, and imagines genetic variants with effects throughout life. The effects of different mutants on mortality are allowed to change non-linearly with age. These more recent models can be integrated more easily with physiological processes and are more realistic than earlier formulations, yet they still predict that specific kinds of mutants will be selected out of the population more slowly than others (those whose effects increase with age, such as one that might increase LDL cholesterol, for an example not used by Wachter). Given rates of entry of new mutants and rates of exit through selection, there will be a tendency toward age-based genetic load that can account for Gomperz-like aging.

Discussion and exchanges that followed Wachter's presentation point to the direction for the future. Wachter acknowledges that the genetic load explained by mutation accumulation theory is just a tiny part of the genome, and that optimizing selection on genes with pleiotropic effects is a major driver in genetic architecture. The question of what the aging process and mortality curve would look like in the absence of genetic load remains unanswered. So, there is now some clarity of purpose for future research to (1) integrate optimality and mutation accumulation approaches into more adequate theories of genetic architecture and phenotypic changes with age; (2) understand why there is so much persistent heritability of what appear to be important traits that presumably should have been fixed by selection; and (3) discover what genetic architecture underlies both heritability and plastic responses to different environments.

The paper by Weiss is far more cautious about the potential contributions of genetics research; indeed, the apt word might be “pessimistic.” While agreeing in principle that genetics can be used to understand causal mechanisms that underlie age patterns of mortality and morbidity and ultimately life histories, he is not sanguine about “when, where, or even whether a genomic approach is justified.” He identifies a number of core constraints for such an enterprise, including: (1) Identification of causal variants of interesting phenotypes is limited by somatic mutation combining with genetic mutation that combine to create imprecise mappings. (2) Most genes regulate or process other genes, therefore DNA sequences operate only in the context of multi-way interactions that may not occur in the locations where the interacting factors are produced. Thus, local gene function cannot be understood from local mapping “hits” alone. (3) Epigenetic effects that affect gene action can mimic familial correlations and can also involve enzymes that are coded by genes located elsewhere in the genome. In short, it's complicated. And, as noted above, the effects of genes cannot be separated from the context in which they operate.

Context, context, context. It was a recurring theme throughout the workshop, and recurs throughout the papers in this volume. Here, we present a few examples. Weiss talks not only about the context of multiway interactions at the micro level, but also the context of the genomic background and environmental experience of each individual. Kuzawa and Eisenberg provide additional examples of how context plays into intergenerational transmission of environmental effects in their paper. Substantial notice has been given to the effects of early environmental experience on adult outcomes both in humans and nonhuman animals, but their paper and presentation highlight the pathways through which environmental effects can be transmitted to descendants: phenotype-to-phenotype transmission via placenta, breast milk, or parental behavior; direct germline epigenetic inheritance; and possibly, plasticity in telomere length as a potential transgenerational influence on lifespan. These pathways can affect such characteristics as obesity and diabetes, metabolism, stress physiology, memory, affect regulation, and even mortality.

Weiss proposed one potential direction for further research to be drawn from synthesizing these papers. He suggested that, at least for the time being, genetic work should be focused on the few diseases for which large effects of single nucleotide variants can be detected. Another possibility is that attention should be directed to understanding the sources of missing heritability by taking advantage of what is now known about regulation of gene expression, and by building more adequate functional models of interactions among genes. Models of the functional design underlying important biological traits, such as energy management, inflammation, and social interactions, should help guide the search for organizational principles underlying gene regulation, gene-gene interactions, and gene-by-environment interactions. Such models may help identify the processes underlying the heritability of complex phenotypes.

Tung's paper proposes a second potential direction for future research, one that also emphasizes the importance of functional analysis. She argues that studying the functional organization of the genome, particularly its role in gene regulation, is a fruitful approach to understanding the comparative biodemography of aging. The core idea is that measures that get at variation in gene regulation, especially when viewed across the genome, can provide insight into how variation in environmental factors, including social experience, affect aging. Her paper lays out an ambitious agenda for integrating studies of population health and aging on the demographic side with, on the genetics side, functional genomic strategies for understanding the effects of the social environment.

Context matters for genes. It matters for individuals. It matters for societies. It matters for frogs and baboons, for turtles and humans, for macaques and snakes and birds. Very simply, it matters.


When Between Zeus and the Salmon was published in 1997, the application of ethics to biodemography seemed simpler—although maybe it wasn't. Drosophila and nematodes are not warm and cuddly, and their use in experiments on longevity did not immediately raise the kinds of questions that come up when primates and other vertebrate animals are subjects of study, when anthropology and biology are integrated into biodemography. Even in the 1990s, there was discussion of the results of the experimental manipulation of rodents and monkeys; it's just that not much time was spent in consideration of the ethics of “animal models.” This workshop highlighted the increase in cross-disciplinary integration, and also threw a spotlight on lack of sophistication regarding the ethics of nonhuman animal research and on human research in the age of “big”—no, make that “massive”—data. The workshop presentations stimulated discussion about the scientific necessity for and ethical considerations in captive-animal research.

One concern that arose in discussion is the inherent tension between the overwhelming scientific imperative of making data available for all researchers and the equally compelling need—indeed, it's usually a promise—to protect the confidentiality and privacy of those who provide cheek swabs or other specimens to researchers. These competing goals are not new, but they have taken on new and increased urgency: The greater expense of studies leads to greater pressures to make data publicly available, and the need for greater statistical power encourages pooling data across studies, while increasing internet access to data makes individual privacy and the confidentiality of data ever-receding targets. Conducting Biosocial Surveys (National Research Council, 2010) made a start on considering these issues—at least with respect to the proliferating number of demographic surveys that incorporate the collection of biospecimens. A strong recommendation in that volume was that data sharing plans be carefully designed and vetted; a corollary was that the National Institutes of Health (NIH) prepare and publish guidelines for acceptable plans. The conclusions regarding protecting confidentiality are particularly instructive. Other recommendations (pp. 76-79) included the following: explicit informed consent for any uniquely identifying data (including genetic data); encryption of such uniquely identifying data on institutional or personal computers; sharing data that change little over time only under restricted conditions; the development by the NIH of standards and procedures for sharing confidential data; periodic expert audits of confidentiality and computer security. To date, few of these recommendations have been implemented, but perhaps the proposed changes to the Common Rule10 on human subjects, if they are adopted, will address many of these concerns.

Studies of nonhuman animals were a more prominent part of this workshop than those related to previous NRC biodemography publications. In his commentary, Jeffrey Kahn suggested that the criteria the NIH now applies to the use of chimpanzees in research could serve as a starting point for developing guidelines for the use of other nonhuman primates and other animals. He put forward three (minimal) criteria proposed for the use of chimpanzees in research: (1) that the research be critical to human health, not just “interesting”; (2) that no other acceptable model is available; and (3) that it would be unethical to perform the research on human subjects. Chimpanzees in Biomedical and Behavioral Research: Assessing the Necessity (National Research Council, 2011) also mandated that the animals be maintained in ethologically appropriate environments and that the animals “acquiesce” (i.e., do not object) to the research.

These guidelines themselves raise additional questions, for example, how “acquiescence” to invasive experimentation can be a meaningful indication of “agreement,” or how such acquiescence—assuming it could be obtained—could be separated from a response to positive (or negative) reinforcement. How necessary is experimental research on nonhuman animals? As reported in the NIH Record,11 former NIH Director Elias Zerhouni has argued that “we need to refocus and adapt new methodologies for use in humans to understand disease biology in humans” because it is becoming clear that animal research on human diseases is not producing the results that are needed.

Since its original publication, the chimpanzee report has been modified to permit non-invasive behavioral observation on chimpanzees in their natural environments. The papers in this volume attest to the methodological advances that have been made in measuring stress, health, and social relationships among nonhuman primates in that context.


Humans are complex, nonhuman animals are complex, and all exist within different contexts. But, despite the differences between mice and men—as Marmot and Sapolsky note, humans are not “simply baboons in clothes”—perhaps we can learn from studies of nonhuman animals. The contribution by Alberts and her colleagues takes a fresh look at the male-female mortality paradox by comparing data on baboons and humans. Briefly, the “paradox” is the observation that while women live longer than men in virtually all modern societies, they also suffer from poorer health. The Alberts et al. wide-ranging review of the available historical data suggests that for humans, with some exceptions, both the female advantage in mortality and the health-survival disjunction is evident. Among baboons, however, while females experience lower mortality, there is little evidence to suggest that females have worse health. They conclude that the delayed mortality advantage has a long evolutionary history, but the male health advantage does not. They propose explanations: (1) that the rapid changes in sex steroid concentrations observed in women over age 50 are not seen in baboons, and (2) that the measures of health that are typically used for women are impossible to collect among wild baboons. These proposals themselves lay out an agenda for future research. One might speculate about how their results link back to the evolutionary pathway proposed by Ellison and Ottinger regarding post-reproductive survival. What would be seen if post-reproductive baboons were commonly observed? Or what could be learned about the paradox if it were possible to measure health in the few other species (some toothed whales for example, see Ellison and Ottinger in this volume) that have long periods of post-reproductive life?

Papers by Johnson and Carey and by Miller and Bronikowski and their colleagues take us farther afield, into the realms, respectively, of social insects (particularly honeybees) and ectothermic vertebrates (specifically painted turtles, garter snakes, and yellow-legged frogs). What are the commonalities? Like many of the papers discussed here, the work by Johnson and Carey points to the importance of considering multiple levels of investigation, from molecular and individual to colony (or society) and the role of intergenerational transfers in survival, growth, and reproductive success. Miller, Bronikowski et al. report that environmental factors, including stress, affected mortality of the animals they studied, and like humans and the rhesus macaques discussed by Suomi at the workshop, the quality of early life experience and subsequent resilience were related: among the long-lived ecotype garter snakes, inferior early life conditions provided inadequate preparation for substandard subsequent environmental circumstances. Evidently, even among garter snakes, the arm of childhood reaches long and strong into later life.


All aspects of people's lives, from birth to death, are affected by their social relationships and their larger social context. In this, there is continuity with many nonhuman primate relatives. Interdependence is deeper in the human case, however, because a division of labor in the production of resources, and the redistribution of those resources, are universal features of human societies.

Scientists are now getting a glimpse of the mechanisms through which social conditions can affect gene activity, both within the lives of individual organisms and across generations. Still missing, though, is a functional understanding of those mechanisms. It is not known, for example, whether patterns of methylation during development and aging represent adaptive responses to phenotypic conditions. Still, in light of what appears to be a long evolutionary history of social interdependence in our species and in our ancestral primate line, it seems likely that natural selection has acted on how gene activity—and cellular machinery more generally—change in response to changes in social environments and phenotypic conditions. Development of theory that considers functional relationships may help organize the complexity of those mechanisms.

Initial attempts to explain significant variation in health through the identification of single nucleotide polymorphisms may be faltering, and more of the same may produce diminishing returns. However, scientists are coming to a deeper understanding of the nature and nurture duality. These insights have come about not simply through blurring the distinctions between the two, but through a more nuanced grasp of their interplay over diverse time scales during the life course of organisms and over evolutionary time. There is no map for how to explore this new territory, but a greater integration of bench science with research into the life histories of whole organisms in their social contexts and natural habitats is a path forward.


We thank Barbara Torrey for her thoughtful suggestions for this introduction, Jeffrey Kahn for his patient and constructive comments on the section on ethics, Dana Glei for her summary of findings on stress and dysregulation, and James Carey for his video-recordings of workshop presentations and discussions. The Behavioral and Social Research Division of the National Institute on Aging has been a stalwart supporter of biodemography, providing not only material support, but vision. In particular, Richard Suzman has been unflagging in his efforts to promote and defend the field; he has encouraged, engaged, argued, periodically prodded, kibitzed, inspired, and served as a catalyst for new collaborations and the opening of new areas of research. As biodemographers, we have incomplete and imperfect data, and we are but imperfect scientists with perpetual—as Richard has eloquently put it—training wheels on as we repeatedly enter into new areas of research with new challenges. Following his example of courage, we soldier on. It's a wonderful time for biodemography.


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Elliott, T.S. (1932). Sweeney Agonistes: Fragments of an Aristophanic Melodrama. Fragment of an Agon. London, England: Faber and Faber.


Burton, R. (1631). The Anatomy of Melancholy. [Reprinted 1924.] New York: Empire State Book Company (p 358).


Forster, E.M. (1910). Howard's End. London, England: Edward Arnold.

Copyright 2014 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK242461


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