Category Archives: Archaeology and anthropology

Archaeology and anthropology

Michael Purugganan

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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.

Dolores R. Piperno

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National Museum of Natural History, Washington DC, and Smithsonian Tropical Research Institute, Balboa, Republic of Panama

An archaeologist tells how her research interest sheds light on the history of her favourite fruit.

My mother gave me a lot of sage advice during my childhood. This sometimes countered prevailing wisdom, such as her recommendation that I should eat bananas, not apples, every day.

The nutritional qualities of bananas were underappreciated when I was growing up in Philadelphia, Pennsylvania, although their value as a crop had been recognized millennia before.

A recent paper (B. Lejju et al. J. Archaeol. Sci. 33, 102–113; 2006) reports that bananas were being cultivated in Africa as long as 5,000 years ago.

The investigators reached this conclusion by studying phytoliths — highly durable pieces of silica that form in plant cells — that had been dug up in Uganda. I use phytoliths (and starch grains) in my own research into the history of agriculture, so it was more than just my fondness for bananas that drew me to this paper.

Phytoliths tell us which crops grew where and when, and so in turn can teach us about human cultures. Part of what makes this finding interesting is that bananas aren’t native to the African continent. Wild bananas grow in eastern Asia, Australia and Melanesia. Hence the Ugandan bananas represent ancient human transport, probably through trade across the Indian Ocean with societies that were already growing the plant.

The age of the banana phytoliths also rivals presently available dates for the domestication of important, indigenous plants such as sorghum. However, I suspect that when phytolith and starch-grain analysis is applied to the history of native African crops, the date of their domestication will be pushed further back.