Crop Origins

16 November 2008

Interview with

Martin Jones

Rice PlantChris - One of the other things that is very important to food is plant sources and one of the things that we see commonplace today in the domesticated crops we grow them in fields, we harvest them and we eat them. Was that always the case? Martin Jones is also with us from Cambridge University. Welcome Martin. What about when people began to first domesticate plants?

Martin - We've been eating grass seeds, and let's remember we've been eating them for at least 25,000 years.

Chris - How do you know that?

Martin - There are some sites, for example a site on the sea of Galilee, which captured the remains of wild barley seeds along with a whole range of other things: of fish, birds and other things they ate. They were found on the fire and in addition that site on the sea of Galilee had grinding stones. In the cracks of the stones were small bits of silica. Under a microscope we can identify them as coming from grass seeds.

Chris - So our history with plants goes back a long time. We've got that documented but it's a bit different to just go gathering plants than to just grow them for the purpose of eating them or using them. When do we think that happened?

Martin - We can see that something big happened to the form of the plants around 10,000 years ago. Between 9 and 10 thousand years ago in different parts of the world: in southwest asia but also in parts of china you can see plants changing their form. They're changing their form in such as way as they need the farmer to sew them. That's the threshold that we think of as domestication when the plant can no-longer survive in the wild. It's become dependent on the farmer to sew it.

Chris - This would have been because people were selecting breeds of plants that would give them very good yields but obviously the payback for the plant was it needed to be nurtured.

Martin - Well you can see it that way. Also it's the plant evolving so the plant is, in a sense, going for an option that's good for the plant. It's the plant evolving rather than the humans and what we can see is there's enough human predators doing certain things for the plant to switch that way. I think we're thinking of these evolutionary processes as two-sided. Both the humans and the plants are evolving together.

Chris - That would put the first farmers around 10,000 years ago. What sorts of crops were they growing?

Martin - They'd have grown crops that were slightly familiar to us. They'd have grown wheat and barley. They wouldn't be the same wheat as we have in our bread today. In fact the types of wheat, the species of wheat that they were growing are now quite rare. They have names like einkorn and emmer. There are just very few places, normally hilly places, where crop salesmen don't get to in Europe and Africa where you can find them still growing. In China they would be rice and millet. Millet we're most familiar with as birdseed but in fact a lot of people still eat millet in North China.

Chris - If you look at the genetic history of the plant what can the DNA in the plants tell you about these various transitions? How would you go about interrogating the plants genetics to find out when these transitions happened?

Martin - What we're finding the answer to that question sis changing every year. Genetics is changing so fast and what we know now is that the DNA in the plant has a massive amount of historical information about what's happened to it. That comes in two forms. On the one hand there's a lot of DNA that doesn't seem to be doing much except slowly evolving and that acts rather like the tachometer in a lorry. It traces a record of the journey the crop's taken through time. Some DNA you can treat as a marker of the journey and you can trace back the family tree of the plant and where it's spread to and where it's started from. Also the DNA that's making the bits of the plant we're beginning to realise that can tell us a lot too. The reason is that as plant agriculture spreads around the world it spreads into different environments and those genes do accordingly.

Chris - When people moved they presumably - if they had a good yielding crop they'd have taken some of it with them. So that can tell you not just where the plants went but where the people went.

Martin - In fact, now because genetics has affected every branch of archaeology you can have a group of different geneticists. You can have one looking at the human genes and forming maps and journeys of spread. You can have another geneticist looking at the crop genes and doing a map of the spread there. You can have a third set of geneticists looking at the disease genes. They're all tracking the same pathways which are the pathways of our human past.

Chris - What does this tell us about the way that humans got around the earth? What impact do the changes you see in the plants have on what we understand about early human civilisations and people getting together in communities?

Martin - One thing to bear in mind is that humans were getting round the earth before domestication happened and so on the one hand you can see humans going to the northerly latitudes way before agriculture. By 30-40,000 years ago there are humans in the Arctic Circle and that does say something about how they were interacting with animals and plants. You can see also farmers getting into the Arctic Circle. For example, we've done some work with barley and that has shown a similar picture.

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