This volume takes a new approach to bridging the cultures of science and the humanities. The editors and contributors formulate how to develop a new shared framework of consilience beyond mere interdisciplinarity, in a way that both sides can accept.

In the study reported here we examined the impact of population size and two proxies of risk of resource failure on the diversity and complexity of the food-getting toolkits of hunter–gatherers and small-scale food producers. We tested three hypotheses: the risk hypothesis, the population-size hypothesis, and a hypothesis derived from niche construction theory. Our analyses indicated that the toolkits of hunter–gatherers are more affected by risk than are the toolkits of food producers. They also showed that the toolkits of food (...) producers are more affected by population size than are the toolkits of hunter–gatherers. This pattern is inconsistent with the predictions of both the risk hypothesis and the population-size hypothesis. In contrast, it is consistent with the predictions of the niche construction hypothesis. Our results indicate that niche construction has affected the evolution of technology in small-scale societies and imply that niche construction must be taken into account when seeking to understand technological variation among food producers and the technological changes that occurred in association with the various transitions to farming that have occurred over the last 10,000 years. (shrink)

In 1923, Sir Arthur Keith proposed that many common back problems are due to the stresses caused by our evolutionarily novel form of locomotion, bipedalism. In this article, we introduce an updated version of Keith’s hypothesis with a focus on acquired spinal conditions. We begin by outlining the main ways in which the human spine differs from those of our closest living relatives, the great apes. We then review evidence suggesting there is a link between spinal and vertebral shape on (...) the one hand and acquired spinal conditions on the other. Next, we discuss recent studies that not only indicate that two common acquired spinal conditions—intervertebral disc herniation and spondylolysis—are associated with vertebral shape, but also suggest that the pathology-prone vertebral shapes can be understood in terms of the shift from quadrupedalism to bipedalism in the course of human evolution. Subsequently, we place the aforementioned findings under an umbrella hypothesis, which we call the “Evolutionary Shape Hypothesis.” This hypothesis contends that individuals differ in their propensity to develop different acquired spinal conditions because of differences in vertebral shape that relate to the evolutionary history of our species. We end the article with some possible directions for future research. (shrink)

Variation in the durations of exclusive breastfeeding (exBF) and any breastfeeding (anyBF) is associated with socioecological factors. This plasticity in breastfeeding behavior appears adaptive, but the mechanisms involved are unclear. With this concept in mind, we investigated whether durations of exBF and anyBF in a rural Maya population covary with markers of a form of socioecological change—market integration—and whether individual factors (individual learning, physiological plasticity) and/or learning from others in the community (social learning, norm adherence) mediate these changes. Using data (...) from 419 mother-child pairs from two Guatemalan Maya villages, we fit a bivariate linear mixed model. The model compared exBF and anyBF among children from households of varying degrees of market integration whose mothers follow what we inferred to be local infant-feeding norms. It controlled for other factors expected to affect breastfeeding durations. We found evidence that exBF is associated with whether mothers follow their population’s infant feeding norms, but no evidence that exBF is associated with the household’s level of market integration. Conversely, anyBF is significantly associated with the household’s market integration, but not with the villages’ inferred norms. Because deviations from exBF norms are likely to result in infant mortality and reduced fitness, we hypothesize that the incentive to conform is relatively strong. Relatively greater individual plasticity in anyBF allows mother-child pairs to tailor it to socioecological conditions. Deviations from anyBF norms may be tolerated because they may provide later-life health/fitness payoffs, while posing few risks to infant survival. (shrink)