Many of our staple food crops, including wheat, oats, barley, rye and maize, are members of the grass family which have become greatly modified since the dawn of agriculture by inadvertent and later deliberate human selection. It is possible that we too have become genetically modified over the millennia to increase our tolerance of cereals, in a way parallel to our evolution of tolerance to milk. Starchy cereals such as wheat and oats cannot have featured prominently in our diets before the Agricultural Revolution. Unlike oranges and strawberries, cereal seeds do not 'want' to be eaten. Passing through an animal's digestive tract is no part of their dispersal strategy, as it is of plum and tomato seeds. On our side of the relationship, the human digestive tract is not able, unaided, to absorb much nutriment from seeds of the grass family, with their meagre starch reserves and hard, unsympathetic husks. Some aid comes from milling and cooking, but it also seems conceivable that, in parallel with the evolution of tolerance to milk, we might have evolved an increased physiological tolerance to wheat, compared to our wild ancestors. Wheat intolerance is a known problem for a substantial number of unfortunate individuals who discover, by painful experience, that they are happier if they avoid it. A comparison of the incidence of wheat intolerance in hunter-gatherers such as the San, and other peoples whose agricultural ancestors have long eaten wheat, might be revealing. If there has been a large comparative study of wheat tolerance, like the one that has been made of lactose tolerance across different tribes, I am unaware of it. A systematic comparative study of alcohol intolerance, too, would be interesting. It is known that certain genetic alleles make our livers less capable of breaking down alcohol than we might wish. In any case, co-evolution between animals and their food plants was nothing new. Grazing animals had been exerting a kind of benevolent Darwinian selection on grasses, guiding their evolution towards mutualistic co-operation, for millions of years before we started domesticating wheat, barley, oats, rye and maize. Grasses flourish in the presence of grazers, and they probably have been doing so for most of the 20 million years since their pollens first announce them in the fossil record. It is not, of course, that individual plants actually benefit by being eaten, but that grasses can withstand being cropped better than rival plants can. My enemy's enemy is my friend, and grasses, even when grazed, thrive when herbivores eat (along with the grasses themselves) other plants that would compete for soil, sun and water. Grasses became ever more able to thrive in the presence of wild cattle, antelopes, horses and other grazers (and eventually lawnmowers), as the millions of years went by. And the herbivores became better equipped, for example with specialised teeth, and complicated digestive tracts including fermentation vats with cultures of micro-organisms, to flourish on a diet of grass. This isn't what we ordinarily mean by domestication, but in effect it is not far from it. When, starting about 10,000 years ago, wild grasses of the genus Triticum were domesticated by our ancestors into what we now call wheat, it was, in a way, a continuation of what herbivores of many kinds had been doing to the ancestors of Triticum for 20 million years. Our ancestors accelerated the process, especially when we later switched from inadvertent, accidental domestication to deliberate, planned selective breeding (and very recently scientific hybridisation and genetically engineered mutations) The Ancestor's Tale, Richard Dawkins

• published: 25 Feb 2011
• views: 4312