Strategies for risk communication: evolution, evidence, experience.

This volume presents the proceedings of the symposium entitled Strategies for Risk Communication: Evolution, Evidence, Experience. The symposium was held in Montauk, Long Island, New York on May 15-17, 2006. It explored practical methods and robust theories of risk communication informed by recent research in risk perception, neuroscience, and the evolutionary social sciences. The symposium focused on what experimental, survey, and brain imaging research has uncovered about how humans process and perceive uncertainty and risks and what the evolutionary history of humans suggests about how we understand and respond to risks. The purpose of the symposium and of this collection of papers is to begin to synthesize the findings from these diverse fields and inform the development of practical strategies for risk communication.

Evolved altruism, strong reciprocity, and perception of risk.

Humans have a long history of coping with particular recurring risks. We expect natural selection to have resulted in specific physiological and psychological adaptations that respond well to these risks. Why, then, does it seem so difficult to communicate risk? We suggest that the human mind has been structured by natural selection to use a mental calculus for reckoning uncertainty and making decisions in the face of risk that can be substantially different from probability theory, propositional calculus (logic), or economic rationality (utility maximization). We argue that this is because of the unique armamentarium of strategies humans have evolved to cope with the risks faced during our long history living as hunter-gatherers. In particular, we believe the risk of social contract violation (not contributing a fair share to cooperative endeavors) was an important selective factor because reciprocity, reciprocal altruism, and cooperation are primary adaptations to the most important risks our ancestors faced.

Demography, life history, and social structure in Propithecus diadema edwardsi from 1986-2000 in Ranomafana National Park, Madagascar.

Prosimian lemurs differ fundamentally from anthropoid primates in many traits related to social structure. By exploring the demography of Milne-Edwards' sifakas (Propithecus diadema edwardsi), and comparing it to other well-studied primates, we explore the effect of demographic and life-history factors on social structure. Specifically, we compare lemur survivorship and fertility patterns to two published composite models: one created for New World and another created for Old World monkeys. Using longitudinal data collected on individual Propithecus diadema edwardsi from four study groups from 1986-2000 in Ranomafana National Park, Madagascar, we quantify 1) group composition, 2) birth seasonality, 3) interbirth interval, 4) life-table values, and 5) population growth estimates. The mortality, survivorship, and life-expectancy schedules indicate high infant and juvenile mortality. Fertility remains high until death. The intrinsic rate of increase and net reproductive rate indicate a shrinking population. We suggest that high mortality rather than low fertility causes the observed population decline. While sifaka survivorship closely resembles New World patterns, fertility resembles Old World patterns, i.e., like New World monkeys, few sifakas survive to reproductive age, and those that do, reproduce at a slow rate resembling the Old World pattern. This necessarily impacts social structure. An adult sifaka at the end of her lifespan will have one only daughter who survives to reproductive age, compared to 3.4 for New World or 2.7 for Old World monkeys. Demography limits the formation of large kin-based groups for sifakas, and survivorship and fertility patterns do not easily permit sifakas to form large same-sex family groups.

Evolutionary approach to below replacement fertility.

The large human brain, the long period of juvenile dependence, long life span, and male support of reproduction are the co-evolutionary result of the human niche based on skill-intensive techniques of resource accrual. The regulation of fertility under traditional conditions is based upon a co-evolved psychology and physiology where adjustments of investment in offspring depend upon the returns to skill and mortality hazards. When all wealth is somatic, the hormonal system controlling ovulation and implantation translates income into genetic descendants. In modern society the existence of extra-somatic wealth is a critical condition to which our evolved proximate physiological mechanisms do not respond. However, psychological mechanisms regulating parental investment in offspring quality may lead to greater and greater investment in own and offspring education, a smaller desired family size, a delay in the onset of reproduction, and a reduction in the total numbers of offspring produced. This delay in reproduction can cause many individuals to produce fewer children than desired because fecundity falls during the reproductive part of the life course. As more individuals in a society follow this pattern, more will fail to reach their desired family size. At the same time the effective use of birth control decreases the numbers of families producing more children than desired. Below replacement fertility can result. Predictions from this model were tested using data from the National Survey of Families and Households and the Albuquerque Men study.