A disproportionately large number of the most important human food plants is cyanogenic. The accumulated research of numerous people working in several different disciplines now allows a tenable explanation for this observation. Cyanogenesis by plants is not only a surprisingly effective chemical defence against casual herbivores, but it is also easily overcome by careful pre-ingestion food processing, this latter skill being almost exclusive to humans. Moreover, humans have the physiological ability to detoxify cyanide satisfactorily, given an adequate protein diet. It appears that early in the domestication of crop plants the cyanogenic species would have been relatively free of pests and competitive herbivores, as well as having good nutritional qualities, and thus ideal candidates for cultivation by the first farmers.