Category: Domestication

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European aurochs DNA in domestic cattle

A study  ((Edwards CJ et al., 2007. Mitochondrial DNA analysis shows a Near Eastern Neolithic origin for domestic cattle and no indication of domestication of European aurochs. Proceedings Royal Society B 274:1377-1385)) just published by the Royal Society sheds some light on the genetic relationship between the European auroch and modern European cattle breeds. Cattle were initially domesticated perhaps around 10,000 years ago in Mesopotamia, and independently in India and probably Africa. As animal agriculture spread into Europe from the Middle East, domesticated cattle must have coexisted with wild European aurochs for some time, since aurochs in Europe didn’t die out until much later (in fact, the last aurochs appear to have lived in Poland around 1627). Analysis of contemporary as well as ancient mitochondrial DNA from Middle Eastern and Central European archaeological sites now seems to suggest that European cattle originated solely from Middle Eastern aurochs, and that no introgression of European auroch genes into domesticated cattle occurred during their long coexistence.

However, an earlier study  ((Götherström A et al., 2005. Cattle domestication in the Near East was followed by hybridization with aurochs bulls in Europe. Proceedings Royal Society B 272:2345-2350)) did show that there had indeed been introgression of auroch Y chromosomes into Northern and Central European domestic cattle and that these Y chromosome markers still exist in some European breeds. Of course, what might seem contradictory really isn’t: mitochondria are strictly inherited from one’s mother, and the mating of domestic cows with auroch bulls wouldn’t have left any mitochondrial evidence. It would be interesting to know whether such hybridization occurred surreptitiously or intentionally, which of course would suggest that early framers knew something about the benefits of cross-breeding.

From H. Michael Kubisch.

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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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