The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Introduction Part I: 1. The Steppe Highway: the rise of pastoral nomadism as a Eurasian phenomenon 2. Bronze, iron and gold: the evolution of nomadic cultures on the northern frontier of China Part II: 3. Beasts and birds: the historical context of early Chinese perceptions of northern peoples 4. Walls and horses: the beginning of historical contacts between horse-riding Nomads and Chinese states Part III: 5. Those who draw the bow: the rise of the Hsiung-nu Nomadic Empire and the political unification of the Nomads 6. From peace to war: China's shift from appeasement to military engagement Part IV: 7. In search of grass and water: ethnography and history of the North in the Historian's Records 8. Taming the North: the rationalization of the nomads in Ssu-ma Ch'ien's historical thought Conclusion.

Ancient China and its Enemies: The Rise of Nomadic Power in East Asian History . By Nicola Di Cosmo. Cambridge: Cambridge University Press, 2002. ix, 369 pp. $70.00 (cloth).

The two East Asian millets, broomcorn (Panicum miliaceum) and foxtail millet (Setaria italica), spread across Eurasia and became important crops by the second millennium BC. The earliest indisputab...

http://journals.sagepub.com/doi/pdf/10.1177/0959683616641742

Millet cultivation across Eurasia: Origins, spread, and the influence of seasonal climate

By the late third/early second millennium BC, increased interconnectivity in the mountains of Central Asia linked populations across Eurasia. This increasing interaction would later culminate in the Silk Road. While these populations are typically lumped together under the title of ‘nomads’, a growing corpus of data illustrates how diverse their economic strategies were, in many cases representing mixed agropastoral systems. These Central Asian low-investment agropastoralists are responsible for connecting the great centers of plant domestication, and through a process of experimentation and exchange shaped economies across the Old World. In this article, I synthesize the evidence for the movement of agricultural technology through this region, which ultimately brought southwest Asian and East Asian crops together for the first time. By the Late Bronze Age, a specific package of agricultural crops had developed across the entire mountain corridor, including broomcorn millet, peas, naked six-row barley, and highly compact free-threshing wheat. Each of these crops has a distinct narrative, and I approach the topic of their spread individually. I also show that agriculture did not spread across the steppe during the Bronze Age and that crops cultivated in the forest-steppe of Eastern Europe were distinct from those of the mountain corridor.

Agriculture in the Central Asian Bronze Age

The history of cultural exchange in prehistoric Eurasia (CEPE) has been widely investigated. Based on archaeological evidence, this process is thought to date back to at least the early Bronze Age, although details about timings and routes remain unclear. It is likely that CEPE promoted the spread and exchange of crops that originated in different parts of Eurasia; since these remains can be definitely identified and directly dated, they provide ideal research materials to explore the history of CEPE. In this paper, we review the available archaeobotanical evidence and direct radiocarbon dates for crop remains, alongside carbon isotopic data from human bones unearthed from prehistoric sites in Eurasia, in order to investigate the history of the spread of millet crops, and wheat and barley, that were first domesticated in the eastern and western parts of Eurasia during prehistoric times. In combination with other archaeological evidences, we discuss the history of CEPE. Our results suggest that wheat and barley were domesticated in western Asia around 10500 a BP, spread into Europe and western Central Asia before 8000 a BP, and reaching eastern Central Asia and northwestern China between 4500 and 4000 a BP. Data show that both broomcorn and foxtail millet were domesticated in eastern Asia before 7700 a BP, spread into eastern Central Asia between 4500 and 4000 a BP, and into western Asia and Europe prior to 3500 a BP. Wheat, barley, and millet crops were first utilized together in eastern Kazakhstan within Central Asia around 4400 a BP, the region where earliest CEPE is likely to have taken place. These crops were mixedly used mainly in eastern central Asia and northwest China between 4500 and 3500 a BP, and then across the Eurasia before 2200 a BP. The results of this study suggest that transcontinental CEPE might have been initiated during the fifth millennium, before intensifying during the Bronze Age to lay the foundations for the creation of the ancient Silk Road during the Han Dynasty (between 202BC and 220AD).

Exploring the history of cultural exchange in prehistoric Eurasia from the perspectives of crop diffusion and consumption

https://isiarticles.com/bundles/Article/pre/pdf/17124.pdf

Katherine Haas

Papers

Subsistence and social change in central Eurasia: stable isotope analysis of populations spanning the Bronze Age transition