“The whole world is mostly perennials,” says USDA geneticist Edward Buckler, who studies corn at Cornell University. “So why did we domesticate annuals?” Not because annuals were better, he says, but because Neolithic farmers rapidly made them better—enlarging their seeds, for instance, by replanting the ones from thriving plants, year after year. Perennials didn’t benefit from that kind of selective breeding, because they don’t need to be replanted. Their natural advantage became a handicap. They became the road not taken.
National Geographic goes back to the fork and rounds up the perennial grain story. Nothing new for readers here, of course, but good to see it in the mainstream. And if you want to see one reason why perennial grains are a good idea, just look at the picture above the article. Easily worth 1000 words.
Why did early farmers select annuals if they were no better? Diamond has argued that they simply used the best plants that were out there and that agricultural societies began where they did because that’s where the few really good food plants were.
Or, should we compare perennial teosinte vs. annual teosinte (but if domestication was based a freak mutation, what could the stone-agers do?).
Perennial rice vs annual rice? There is no perennial rice in China, where rice was domesticated. They tried in India to make modern rice perennial, but yields were low, disease was high. Perhaps they should try harder. Well, I guess they do that at the Land Institute.
You never know, but I would think that it might be a general trait of perennials to put much energy in survival (those deep roots), and less in seed. Which is OK if you eat the roots (or tubers for that matter), but not great if you want the seed.
And we do have domesticated perennials: apples, potatoes (yes, it is a perennial), … Was there no selection for better types in these crops?
Correction: Dorian F. pointed out that rice in China was domesticated from a perennial (the Indian rices are derived from an annual). But it was not dropped. Rather, it was turned into an annual (and still has some perenniality in it left: it ratoons). He mentioned that barley was also selected from a perennial, but farmers annualized it; and that the same was done in the 20th century with what is called “wild rice” in the USA. So this little piece of evidence is that farmers did take the perennials road, but that along the way they selected them into annuals.
Gosh I’m not sure about barley. What’s the evidence for that one?
Aren’t some forms of Teosinte also perennial? I don’t know to what extent they contributed to maize.
Robert: Spot on about the partitioning of production by annuals into (edible) seed. But the key seems to me to be the persistence of the seed of the annual versus the perenniation body (underground storage organ?). What kind of ecology would favour buried seed over buried rhizomes and tubers? One possibility is long dry seasons with above ground disturbance by fire or flood. Most of our early Old World cereals (wheat, barley, sorghum) had awns allowing seed to insert itself deep in cracks in the soil to escape fire and a large enough seed to rapidly dominate subsequent vegetation. Ditto for rice, which could survive flood buried in silt. I think the promotion of agroecology/more diversity has missed out on the ecology of domestication, in habitats that favour large seeded annuals over perennials, which produces monodominant stands of highly edible cereals. In contrast, in regions with less of a dry season, perennial fruits, nuts, and tubers flourish better. The people who domesticated plants knew this and went for quality over quantity: there is no sign that all the current recommendations for ever more diversity take this highly skilled selection of appropriate annual, large-seeded cereal domesticates on board.
Not necessarily all that “spot on”. One would indeed be foolish to try and breed perennial cereals if resource partitioning were fixed. Fortunately it isn’t. The Land Institute has a quite a lot of evidence showing both heritable variation in seed size and mass and responsiveness to selection. Here’s one, and an earlier one, and a very old one indeed. Clearly they have been aware of the problem from the start. Equally clearly, seed yield should not be the only desirable output of more sustainable farming systems.
Perhaps you can improve perennials and make them like annuals, except for the dying bit, I do not know, but can you have the partitioning of wheat and also have 10 m deep roots?
But back to Buckler who said that that perennial plants have been left behind because they did not go through as many cycles of selection, and hence lost comparative advantage. It sounds good, but what is the evidence? What would be a good example of a perennial species that was left behind?
The earliest crops in the fertile crescent were annuals. It would be nice to have examples of a cereal or pulse-like plants that were common in early agriculture in a region but were dropped a long time ago.
Had oaks been annual, would all those cycles have led to the fixation of an always-sweet mutation and would we be eating acorn-bread today? Almonds? I guess trees have other issues: it took a long time before they bore fruit. But would that be a more persuasive general reason why perennials were dropped (if that is the case), that it takes longer to establish a productive perennial crop? Well, perennial (non-tree) plants were domesticated (indeed often in wetter areas, as Dave points out): banana, cassava, still going strong.
Buckler also says “The whole world is mostly perennials”. That is surely true in terms of land cover; but is it also true in terms of the number of species that an aspiring neolithic farmer could choose from? Would a stone-age food gatherer in the orient have gotten more food from perennial than from annual herbs? (By the way, there is a paper about the disadvantage of cultivation in PNAS this week).
Jeremy: The Land Institute has done a lot of work pushing boulders up hills with little to show for it. Our earliest farmers domesticated annual cereals all over the place – I think with justification. For example, Harlan argued that annual species tend to yield more and be more dependable than perennials. And also with reference to wild rices in West Africa, he noted that the annual Oryza barthii seeds abundantly, but O. longistaminata, a perennial, is relatively shy seeded: I’ll go along with this. And in perennial grassland there is the constant problem with fire taking out your crop in the dry season. Why try for perennials when there is minimum till?
There are some excellent larger-seeded perennial grasses such as Spartina spp., Glyceria fluitans and Distichlis palmeri but these grow in mud and are protected from fire. There is also perennial sorghum in Northern Kenya – but this grows in sandy river beds in semi-desert out of harms way from fire and pests.
I have never subscribed to the multifunctional outputs of supposedly sustainable farming systems adopted by developed countries and imposed on developing countries. At a time of greater demand for food and fewer government subsidies for environmental outputs of farming, the developed countries that persist with the multifunctional way and other costly approaches to food production will end up importing soya and maize from Brazil.
Harlan, J.R., (1989) Wild-grass harvesting in the Sahara and Sub-Sahara of Africa. In: Harris, D.R. and Hillman, G.C. (eds.) Foraging and Farming: the Evolution of Plant Exploitation. Unwin Hyman, London, UK, pp. 79-98.
Is nipa (Palmer’s grass), Distichlis palmeri an example of a locally important perennial grain that was dropped. But when, and why? Was it ever cultivated?
Could be remarkable crop, as it grows in salt water. According to Richard Felger, “World hunger can be addressed by developing mesquite and nipa as new global aridland crops.” It is going to be a cliffhanger with salt tolerant rice, no doubt.