ABSTRACT
The common element of all but one of the chapters in this section is the use of stable isotope analyses to characterize and quantify the use of maize in human diet in the Americas (Chapter 21 will be discussed separately). These chapters exploit the fact that maize uses the Hatch-Slack, or C4 photosynthetic pathway, whereas the majority of wild plants used either as cultigens or consumed by herbivorous sources of protein use the Calvin-Benson, or C3, pathway. This distinction results in a large difference in the 13C/12C ratio in the products of photosynthesis in these plants as well as all other biochemical species in them (including proteins). Specifically, the average δ13C of C3 plants is around −26‰, whereas C4 plants today have δ13C values averaging around −12‰. Both of these would have been shifted to values about 1.5‰ more positive in the preindustrial era before the beginning of large-scale burning of fossil fuel. Modern mass spectrometry can easily detect differences in δ13C of 0.1‰, although in most cases larger differences between populations (about 1‰) would be needed to establish significant differences in use of maize in diet, and so on.
