Palaeodietary isotope studies have long assumed C_4 signals in South American archaeological populations to be due to the consumption of maize (Zea mays), which in turn, underlie interpretations important social processes. We presents δ¹³C data from wild plants (n=89) from the south coast of Peru, which may have been significant in the diets of humans and animals in the past. A combination of these with previously published results from domesticates of the Andean region (n=144) brings the proportion of C_4 species likely to have contributed to the human dietary isotopic signal, whether directly or indirectly, to almost one third. This undermines the widespread assumption that maize is the only plant to contribute a C_4 signal to diets. By considering both direct and indirect routes whereby C_4 plants may have contributed to the human isotopic signal we show the need for a reassessment of how palaeodietary studies are interpreted in the Andes, and perhaps elsewhere in the Americas.LC would like to thank the AHRC, the Anthony Wilkins Fund and the Santander Universities Grant for Travel to Latin America for enabling this research. TCO would like to thank the Wellcome Trust.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s10745-012-9509-0
