Chemistry Reference
In-Depth Information
any region of the world thus makes it possible to establish whether the
plant is of type C3 or C4 (Stanford 1993; Van der Merwe 1982).
When plants are consumed as food by herbivorous animals, the iso-
topic signatures in the plants are passed on to the consumers. Therefore,
provided the isotopic signatures of C3 and C4 plants are known, deter-
mining the isotopie signatures in the tissues of herbivorous animals enables
one to determine the relative amounts of C3 and C4 plants that the animals
consumed as food, and to reconstruct their diets. Moreover, since carnivo-
rous and omnivorous animals, including humans, feed on herbivorous
animals as well as on plants, determining the isotopic signatures of the iso-
topes of carbon in tissues of ancient animals and humans makes it possi-
ble to elucidate the components of their diets.
Many isotopic studies provide perspectives on particular aspects of
ancient diets. In the American continent, for example, maize, a
C4
plant, was
a dominant food that played a fundamental role in the development of pre-
historic societies, and its consumption had important health significance. A
study of isotopes in human bone from eastern North America revealed when
maize was adopted as a food and when it became a major component of
human diets. Isotopic analyses of carbon from human tissues disclosed that,
before the ninth century C.E., C4 plants had little or no place in human diets.
Soon afterward, however, C4 plants became part of the diet, a change that
grew more pronounced with the passing of time. By the thirteenth century
C.E., C4 plants (maize) seem to have become a primary human food, repre-
senting as much as 70% of the diet of the inhabitants of the North American
woodlands, for example. A similar change detected also in human remains
from Panama and Venezuela (although the change occurred at different
times than in North America) points to the introduction, also into these
regions, of the cultivation of C4 plants (Ambrose 1987; Larsen 1997). In the
Old World, maize become part of the human diet only after discovery of the
Americas. Other C4 plants, identified in human remains from before that
time, have been studied, including sorghum in Nubia (White and Schwarcz
1989) and millet in central Europe (Murray and Schoeninger 1988) and north-
ern China (Schwarcz and Schoeninger 1991).
Also the stable isotopes of nitrogen, like those of carbon, are fraction-
ated when nitrogen is incorporated into the plants. Determining the isotopic
ratios between nitrogen-15 and nitrogen-14 in animal remains also reveals
information on the diets of ancient animals and humans (White 1999; de
Niro 1987).
