1. Cohen, M. N. The Food Crisis in Prehistory (Yale University Press, 1977).
2. Harlan, J. R. & De Wet, J. M. J. Some thoughts about weeds. Econ. Bot. 19, 16–24 (1965).
3. Hillman, G. C., Colledge, S. M. & Harris, D. R. in Foraging And Farming: The Evolution Of Plant Exploitation (eds Hillman, G. C., Colledge, S. M. & Harris, D. R.) 240–268 (Unwin Hyman, 1989).
4. Zeder, M. A. & Smith, B. D. A conversation on agricultural origins. Curr. Anthropol. 50, 681–690 (2009).
5. Elbaum, R., Zaltzman, L., Burgert, I. & Fratzl, P. The role of wheat awns in the seed dispersal unit. Science 316, 884–886 (2007).