Light shed on ancient heat

Starch is not the first substance that springs to mind when someone mentions chili peppers. What one is interested in is capsaicin, heat. I mean, who cares about the starch in peppers? Linda Perry and her colleagues, that’s who, because by studying starch grains from chili peppers they have shown that peppers were domesticated far earlier, and grown far more widely, than had previously been imagined. Six thousand years ago people were growing and eating chili peppers.

Perry and her colleagues focused on starch grains characteristic of all species of the genus Capsicum. The grains are flattened discs with a central depression, a little like a red blood cell, and three of the species, C. baccatum, C. frutescens and C. pubescens, can be distinguished by distinctive features of the depression. The other two species -- C. annuum and C. chinense -- are much harder to separate from one or more of the others. But all the domesticated chili species are easy to distinguish from wild relatives by their starch grains.

The researchers washed milling stones, tools and cooking shards to obtain starch grain microfossils, and also found them in sediments. The earliest sites, like Loma Alta and Real Alto in Ecuador, are not thought to be sites of domestication of any of the five species of Capsicum. The authors conclude that “these plants must have been domesticated elsewhere earlier than 6000 yr B.P. and brought into the region from either the north or the south”. The best previous evidence was for C. chinense in Peru about 3000 years ago.

Mixed up with the chili pepper starch grains at various sites were grains from maize, achira, arrowroot, manioc, squash, potato, yam and other food species. It was evident that “sophisticated agriculture was practiced ... before the introduction of pottery”.

Quite apart from pushing back the date of domestication of chili peppers, the research is a beautiful example of the coming together of different strands to illuminate the history of domestication. Solid archaeological digs and dating, microscopy to examine remains that used to be ignored, comparative morphology to separate species from one another, cultivated varieties from their wild relatives, and modern from ancient samples. But I find myself thinking more about how those early hot-heads livened up their maize and manioc with a touch of chili, swapping seeds, swapping stories, setting fire to my imagination.

The research is published in Science but you can only access the abstract. One press release is here; another here.