New York University, USA
An evolutionary geneticist wonders why certain crops were ‘invented’ not once but multiple times.
Crop species have always captured my imagination — perhaps because Darwin saw domestication as a model for the evolutionary process, or maybe because I am an inveterate foodie. Whatever the reason, I work on the evolution of crop species as diverse as rice, barley and cauliflower, using genomic methods to trace their origins.
I was struck by two recent molecular studies that indicate that key crops may have evolved more than once in association with different cultures, after Neolithic farmers began to cultivate various wild plants and select desirable traits 12,000 years ago.
Rice seems to have originated from the wild rice Oryza rufipogon separately in China and in India and southeast Asia (J. P. Londo et al. Proc. Natl Acad. Sci. USA 103, 9578–9583; 2006). Meanwhile, barley, which originated once in the Fertile Crescent — a region defined by an arc through Lebanon, Syria, Turkey and Iraq, and home to the oldest archaeological evidence for agriculture — may also have had a second origin in present-day eastern Iran (P. L. Morrell and M. T. Clegg Proc. Natl Acad. Sci. USA 104, 3289–3294; 2007).
Previous genetic mapping studies of the loss of seed shattering in rice and barley suggests that the trait is controlled by different genes in different lineages of these crops. This makes sense in the light of a multiple-origins scenario.
The pattern is not unique — cattle, sheep and goats were also domesticated multiple times. So did different cultures learn how to go about domesticating wild plants and animals from each other, or did they arrive at the same evolutionary solutions independently when faced with similar challenges? Hopefully the genetic data will motivate archaeologists to dig for evidence of how groups of people went about developing these crops.