Biogeochemical methods using stable isotopes and trace elements have been increasingly developed and applied to reconstruct modern and ancient breastfeeding and weaning practices of mammals, including humans, because they offer direct proxies for the dietary intake of subadults. Carbon, nitrogen, and oxygen isotopes have been used to evaluate breast milk lipid, protein, and water intake, respectively. Carbon and sulfur isotopes have been used to estimate the content of weaning foods. The elemental concentrations of Sr and Ba in subadult tissues differ because of the dietary change during the weaning process. For analyses, various tissues have been used, such as hair, nail, blood, and feces for modern mammals and bone and teeth for ancient ones. Of these, trace element analysis of tooth enamel offers a good opportunity for the reconstruction of breastfeeding and weaning practices of the more distant past at finer resolution, although further understanding of the metabolism of trace elements is necessary. There are various tissue-and element-specific advantages and disadvantages, and a combination of different proxies can illuminate practices from various viewpoints. Finally, applying the geochemical reconstruction of breastfeeding and weaning practices to human ecology, primatology, and paleoanthropology is important; basic studies of the underlying physiological mechanisms and technical improvements in the analyses will further highlight avenues for future research. Yrbk Phys Anthropol 156:2-21, 2015. V C 2014 American Association of Physical AnthropologistsThe reconstruction of breastfeeding and weaning practices (BWPs) of ancient human and other mammalian species is one of the most important fields in anthropology, archaeology, evolutionary biology, and history. Infant feeding practices affect the overall health of the population because diet, health status, and growth at a young age have profound effects on an individual's later life (Dettwyler and Fishman, 1992;Katzenberg et al., 1996;WHO, 1998WHO, , 2009Lewis, 2007). Breastfeeding and weaning practices can be viewed from the evolutionary perspectives of life history theory, parental investment, child development, social system, and reproductive strat-

BackgroundNitrogen isotope analysis of bone collagen has been used to reconstruct the breastfeeding practices of archaeological human populations. However, weaning ages have been estimated subjectively because of a lack of both information on subadult bone collagen turnover rates and appropriate analytical models.MethodologyTemporal changes in human subadult bone collagen turnover rates were estimated from data on tissue-level bone metabolism reported in previous studies. A model for reconstructing precise weaning ages was then developed using a framework of approximate Bayesian computation and incorporating the estimated turnover rates. The model is presented as a new open source R package, WARN (Weaning Age Reconstruction with Nitrogen isotope analysis), which computes the age at the start and end of weaning, 15N-enrichment through maternal to infant tissue, and value of collagen synthesized entirely from weaning foods with their posterior probabilities. The model was applied to 39 previously reported Holocene skeletal populations from around the world, and the results were compared with weaning ages observed in ethnographic studies.ConclusionsThere were no significant differences in the age at the end of weaning between the archaeological (2.80±1.32 years) and ethnographic populations. By comparing archaeological populations, it appears that weaning ages did not differ with the type of subsistence practiced (i.e., hunting–gathering or not). Most of -enrichment (2.44±0.90‰) was consistent with biologically valid values. The nitrogen isotope ratios of subadults after the weaning process were lower than those of adults in most of the archaeological populations (−0.48±0.61‰), and this depletion was greater in non-hunter–gatherer populations. Our results suggest that the breastfeeding period in humans had already been shortened by the early Holocene compared with those in extant great apes.

The Okhotsk people were sedentary hunter-gatherer-fishers who lived and prospered in Sakhalin, Hokkaido, and the Kurile Islands during the fifth-thirteenth centuries AD. They expanded rapidly along the north-eastern coast of Hokkaido where archaeological evidence suggests an increasing dependence on hunting marine mammals. In this study, we present the results of carbon and nitrogen isotope analyses of 18 faunal (including two domesticated dogs) and 58 adult human skeletons excavated from the Moyoro site of the Okhotsk culture in eastern Hokkaido. Although the mean human isotope ratios did not differ between sexes, the variances of carbon isotope ratios were significantly greater in males. Carbon and nitrogen isotope ratios suggest that the Moyoro humans and dogs heavily depended on marine foods for their dietary protein intake. The Bayesian mixing model suggests that humans obtained a maximum of 80-90% of their dietary protein from marine mammals, whereas domesticated dogs obtained 2-33%, 3-40%, and 5-45% of dietary protein from brackish-water fish, marine fish, and marine mammals, respectively. This suggests an avoidance of significant dietary overlap between the sympatrically living humans and dogs at the Moyoro site. Significant maritime adaptation would have enabled the subsistence of the Okhotsk people in the harsh northern environment of Hokkaido.

It has been hypothesized that nitrogen fixation occurs in the human gut. However, whether the gut microbiota truly has this potential remains unclear. We investigated the nitrogen-fixing activity and diversity of the nitrogenase reductase (NifH) genes in the faecal microbiota of humans, focusing on Papua New Guinean and Japanese individuals with low to high habitual nitrogen intake. A 15N2 incorporation assay showed significant enrichment of 15N in all faecal samples, irrespective of the host nitrogen intake, which was also supported by an acetylene reduction assay. The fixed nitrogen corresponded to 0.01% of the standard nitrogen requirement for humans, although our data implied that the contribution in the gut in vivo might be higher than this value. The nifH genes recovered in cloning and metagenomic analyses were classified in two clusters: one comprising sequences almost identical to Klebsiella sequences and the other related to sequences of Clostridiales members. These results are consistent with an analysis of databases of faecal metagenomes from other human populations. Collectively, the human gut microbiota has a potential for nitrogen fixation, which may be attributable to Klebsiella and Clostridiales strains, although no evidence was found that the nitrogen-fixing activity substantially contributes to the host nitrogen balance.

The urbanization of the city of Edo, the capital of premodern Japan, has been assumed to be not as a result of natural increase but that of in-migration although this assumption has never been verified. To obtain information on natural fertility in Edo, we analyzed stable carbon and nitrogen isotopes in 46 adult and 84 subadult human skeletons excavated from the Hitotsubashi site (1657-1683 AD: the early Edo period), Tokyo, Japan and reconstructed their breastfeeding period, one of the most important determinants of fertility. Adult females are significantly more depleted in (15) N by 0.7‰ than adult males, suggesting a dietary differentiation between sexes and/or the effect of pregnancy. The changes in the nitrogen isotope ratios of subadults suggest that supplementary foods were introduced around the age of 0.2 years and weaning ended around 3.1 years, which agrees with descriptions in various historical documents of the period. The duration of breastfeeding in the Hitotsubashi population was relatively longer than those in modern industrial and traditional societies and four previously reported populations in medieval and in the industrial England. As later weaning closely associates with longer inter-birth interval for mothers, our data suggest a lower natural fertility for the Hitotsubashi population. Assuming that the proportion of married people was also lower in the major cities of the earlier Edo period, our results support the assumption that Edo developed and increased its population by attracting immigrants during urbanization.