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Demeter's legacy: rapid changes to our genome imposed by diet

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The transition from foraging to farming allowed humans to produce several foods in abundance that were previously scarce. However, early farmers had to adapt to benefit fully from this energy-rich but initially detrimental food supply. Perry et al. recently showed that natural selection has increased the copy number of a gene encoding a starch-digesting enzyme in farming populations. This study illustrates that genetic adaptation to new diets has occurred in humans since the agricultural revolution.

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Agriculture: a poisoned chalice

In most food-producing societies, the concepts of abundance and fertility are tightly linked to agriculture. For instance, Demeter, the Greek goddess of crops, was thought to bring springtime and to nourish youth. This protective role illustrates the common representation of farming as a source of health and abundance. However, archaeological records, including clear signs of anaemia in early farmers’ bones [1], clearly contradict this mythological image. The transition from hunter-gathering to

Adjusting the spit to the pot

Recent studies have demonstrated a clear role for positive selection in the evolution of Homo sapiens, despite the fact that these changes in selective pressure have occurred very recently [3]. The dietary revolution associated with farming societies might have thus imposed a selective pressure sufficiently intense to modify the expression profiles of digestive enzymes. Perry et al. [2] provide support for this idea in their recent study. They assessed the extent to which the consumption of

A vital daily amount of cereals and milk

Perry et al. did not provide classical statistical support for the action of positive selection on AMY1 copy number, because neutrality tests at the inter-species and within-species level have not yet been adapted to copy number variation. However, the widespread occurrence of high AMY1 copy number in unrelated populations with starchy diets does support the hypothesis that these human groups independently acquired extra copies by positive selection, rather than through shared ancestry. This,

Winning the evolutionary race

The observed differences in AMY1 copy number between populations of recent common ancestry (e.g. Siberian Yakut and Japanese) suggest that populations with starchy diets have obtained extra AMY1 copies over the past few hundred generations [2]. The observed frequency of the lactase-persistence allele and its associated variation are compatible with positive selection events beginning only 5000 to 12 000 years ago in Northern Europe, 1400 to 3000 years ago in the Urals, and 3000 to 7000 years ago

What drives human evolution?

Knowledge is more easily transmitted than alleles, so cultural adaptation probably played a key role during the adaptive period accompanying the agricultural revolution. Early farmers processed food to decrease its potential to cause digestive problems (e.g. by adding bacterial lactase to dairy products), thereby using their technical abilities to sustain their demographic explosion. Nonetheless, the work of Perry et al. [2] clearly demonstrates that our genes did not lag behind, but instead

Acknowledgements

Financial support was provided by Institut Pasteur, by the Centre National de la Recherche Scientifique (CNRS), and by an Agence Nationale de la Recherche (ANR) research grant (ANR-05-JCJC-0124–01). E.P. is supported by the Fondation pour la Recherche Médicale (FRM).

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