Category: Domestication

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A prickly question

Carciofi

Dealing with a Carciofo alla Giudea I seldom wrestle also with the more fundamental existential question of what exactly an artichoke is. A flower, of course, although for the most part one is eating bracts and the receptacle. A thistle, too. But beyond that, I have to confess I have never really considered relationships among the various varieties of artichoke nor between the artichoke and its obvious cousin the cardoon (where one eats the blanched petiole, preferably in a tasty bechamel sauce).

Real taxonomists, of course, consider this sort of question all the time. And by and large they have concluded that in the genus Cynara the cultivated artichoke is C. scolymus, with cardoon — wild and cultivated — in a separate species, C. cardunculus. Then again, maybe they all belong to C. cardunculus. And how did they evolve? As crops, artichoke and cardoon are pretty recent, only a couple of thousand years old at most. Which wild species were they selected from?

I need concern myself with these prickly issues no more. A recent paper ((G. Sonnante et al. (2007) On the origin of artichoke and cardoon from the Cynara gene pool as revealed by rDNA sequence variation. Genetic Resources and Crop Evolution 54: 483-495. DOI – 10.1007/s10722-006-9199-9)) from the Institute of Plant Genetics in Bari is clear: artichokes and wild and cultivated cardoons belong to a single species, C. cardunculus. How exactly they evolved is less clear. Cardoon and artichoke were domesticated separately and independently, the artichoke around 2000 years ago and the cardoon 1000 years later “at the beginning of the second millennium AD”. Where all this happened is still mysterious. Artichoke’s origins are probably to the east, while the cardoon was domesticated in northern italy, southern France and Spain. But some of the wild “cardoons” of Spain, which differ considerably from those in the eastern Mediterranean, might be feral artichokes.

All of which is delicious. But beyond knowing more about artichoke and cardoon, these findings should also feed into the rational conservation of the species’ biodiversity, being undertaken thanks to a euros 4 million project in Italy ((For which we thank the photograph above.)).

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Lactose tolerance: independent origins and strong selective pressure

Michael Kubisch has submitted another post, based on an article in Nature Genetics. Unfortunately the full article and a News and Views piece about it are behind a paywall. However, I’ve done some sleuthing to find a few links that give more details on the story, which I’ve added at the end. As Michael noted, the article is “not about genetic diversity of agricultural species, but how agriculture has affected human genetic diversity”. That’s good enough for us.

The ability to digest lactose, one of the primary carbohydrates in milk, varies widely among adult human populations. In some European countries nearly 90% of individuals can tolerate lactose, while the incidence in some Asian countries is as low as 1%. The inability to digest lactose is caused by a decline in lactase, the enzyme that breaks down lactose into sugars that can be absorbed into the blood stream. This decline starts shortly after weaning and most likely reflects the fact that until animals were domesticated, milk was simply not a staple of human diets. Lactose tolerance, or lactase persistence as it is sometimes called, in turn is facilitated by a continuous production of lactase throughout adulthood. Not surprisingly, lactase persistence appears to be closely linked to whether a population has traditionally practiced a pastoral or an agricultural lifestyle.

This new study examined the incidence of lactase persistence in several African populations. Based on analysis of genetic markers the authors of the study conclude that the trait appears to have evolved not only independently from Europe, but also more than once in Africa itself. Given that the prevalence of the trait is so high in some populations and domestication of milk-producing animals only goes back 12000 years or so, which is a mere blink of an eye in evolutionary times, milk consumption must have provided a significant benefit for human survival.

Those links:

 

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Hai chihuahua!

A DNA study suggests that small dogs started to appear about 10,000 years ago as a result of a mutation in a single gene (called IGF-1). I wonder if something similar will be found in other domestic animals.

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Domestication

Michael’s post on water buffalo genetic diversity and domestication reminded me that I was intending to point you all in the direction of Dienekes’ Anthropology Blog. Although Dienekes mainly blogs about the genetic diversity and evolution of humans, he does occasionally link to papers on animal domestication and related issues. He has an RSS feed, which makes it easy to monitor his blog. In the past couple of years he has pointed to interesting papers on:

Incidentally, a great paper reviewing the use of genetics and archaeology to document domestication came out last year and you can see the abstract here. Now, what’s really needed is for someone to bring together the human, livestock and crop genetic data.