No answers: we just don’t know. But Bruce Smith, whose book on The Emergence of Agriculture remains one of the best, recently told an audience at Harvard University that although most people see domestication as “a before-and-after kind of event, with hunter-gatherers before and farmers afterward. The reality … was likely far more complex.”
Hard to argue with that, especially in light of increasing evidence that people were both altering the environment to favour wild food sources and cultivating plants without domesticating them. Smith talked a bit about which plants were domesticated — “early-succession species that did well in disturbed environments that humans could create for them” — but not, at least according to the reports, about whether there’s any scope for additional domestications. We’ve asked before: are there any species that people should be cultivating, and possibly domesticating, now that they have so far ignored? My own contenders would be perennial grains. The plants are there; they just need a few thousands year’s work.
Smith’s lecture was part of a series called Food for Thought. ((Harvard brains hard at work.)) We missed one by my old mucker Richard Wrangham, of How Cooking Made Us Human, but tomorrow, 23 February, Samuel Myers will “discuss troubling trends, including climate change and increased threats from pests and pathogens that may constrain the world’s resources, requiring new approaches to sustainable agriculture.” I wonder whether agricultural biodiversity will feature. Someone go, and tell us.
Thanks for alerting us to this lecture and this series. More than 20 years ago, when working on a book, I was (and still am) honored to have Jack Harlan reading the drafts. On the subject of the origins of agriculture, Jack chided me for relying too heavily on his own work. He told me I should be paying more attention to Bruce Smith. Faced with the choice of receiving something like a Nobel Prize or this compliment, frankly, it would be a close call for me.
We who love diversity and love agricultural history should revel in the complexity of the subject. Smith’s profound and insightful work adds so much. I only wish more of us appreciated it. If more did, imagine how differently we in the genetic resources community might see the world. It would, actually, change the world.
In Bruce Smith’s talk on plant domestication he argued that: “[crop] Plants tended to be early-succession species that did well in disturbed environments that humans could create for them.” Well and good for the time after early crops were already grown in fields but Smith is harking back a bit to the ‘crops as weeds’ theories of decades ago that did not take us far.
Melinda Zeder and Bruce Smith in Current Anthropology 50, 681 (2009) recognize the current impasse in crop origins – “talking past each other in a crowded room”. And this despite excellent field research and accumulating knowledge of the time(s) of agricultural origins from probably hundreds of researchers.
Given this impasse, I think ‘early succession’ and ‘disturbance’ heads us off on the wrong track. I have been re-reading Tansley’s classic paper [Tansley A G, 1935. The use and abuse of vegetational concepts and terms. Ecology 16, 284-307]. Tansley challenged early ideas of Clements and Phillips which had suggested that succession was always progressive (from simpler to more complex communities) — and always driven by biotic reactions. But Tansley argued that succession could be retrogressive, moving from more luxuriant to poorer vegetation. Tansley then suggested alternatives to “climatic climaxes”: “edaphic” climaxes determined by soil; “physiographic” climaxes determined by land-relief; “fire” climax determined by burning; and a “mowing” climax determined by periodic cutting. There is even a “plagioclimax” (bent climax) where vegetation comes into equilibrium with any factor deflecting vegetation away from the climatic climax (incidentally, Tansley’s paper has the first use of ‘ecosystem’).
Rather than pinning the ecologically-loaded term “early-succession species” — that is, wimps — on crop ancestors, let’s look at things Tansley’s way. I suggest that the massive stands of cereal crop relatives well documented in the Near East by the likes of Harlan and Zohary (and often related to the origin of agriculture) are in fact species of climax vegetation (and not successional, depending on human disturbance). But what factors determine their climax state?
There are lots of candidates: fire, edaphic features such as gravel fans cause by erosion, flooding of seasonal rivers, grazing by antelopes, and even climatic change. The Younger Dryas around 11,000 years ago was a major climate shift, coming and going in less than1000 years. Along the local ecotone between Mediterrean and Ironao-Turanian vegetation zones the Younger Dryas could have moved the forest-grassland boundary around in both directions and had a major impact on the distribution of large-seeded grasses.
Also, if early crops were directly derived from massive pure stands of wild relatives, then such crops have an ecological heritage of stability. If so, we can now stop worrying about stability based on diversity in agro-ecosystems and start worrying about just what factors once determined the obvious stability of climax vegetation of crop relatives of our major cereals.