One of the nice things about being slow off the mark is that sometimes someone else will do the job for you. So it was with the splashy story in Mother Jones about the decline in apple diversity in supermarkets. Instead of having to point out some of the misleading hyperbole in that story, I can just point you to Alex Tabarrok, an economist with an interest in agriculture and diversity. Better yet, it offers me an opportunity to set Tabarrok himself straight. The view of diversity espoused by “the innovative Paul Heald and co-author Sussanah (sic) Chapman” that Tabarrok lauds is not one shared by many actual plant geneticists. You can talk about variety names, or allele combinations, or genetic distances, and get whatever answer you’re looking for; diversity is higher, lower or unchanged.
The geographical scale over which you measure diversity matters too, and Tabarrok explains that well:
Consider the simplest model (based on Krugman 1979). In this model there are two countries. In each country (or region), consumers have a preference for variety but there is a tradeoff between variety and cost, consumers want variety but since there are economies of scale – a firm’s unit costs fall as it produces more – more variety means higher prices. Preferences for variety push in the direction of more variety, economies of scale push in the direction of less. So suppose that without trade country 1 produces varieties A,B,C and country two produces varieties X,Y,Z. In every other respect the countries are identical so there are no traditional comparative advantage reasons for trade.
Nevertheless, if trade is possible it is welfare enhancing. With trade the scale of production can increase which reduces costs and prices. Notice, however, that something interesting happens. The number of world varieties will decrease even as the number of varieties available to each consumer increases. That is, with trade production will concentrate in say A,B,X,Y so each consumer has increased choice even as world variety declines.
I think something similar can be said of plant breeding. The number of parents in a popular variety’s pedigree may be higher today than it used to be, but the number of parents contributing to today’s popular varieties would, I reckon, be lower than it was, say, 50 years ago.
Looking at Krugman’s model of apple globalization from the Himalayas, an article in the Christian Science Monitor informs us that the first Red Delicious apples arrived their in 1916 in the care of Samuel Evans Stokes, a Quaker Missionary from Philadelphia. Stokes thought apples would flourish in the Shimla hills, and they did. But the climate that attracted Stokes and his apples has changed, and Indian orchardists are finding it hard to respond. Some are apparently giving up on Red Delicious and trying Fuji, Gala and other, newer varieties that may prove better (and happen to be favoured by global apple markets). Some are even switching away from apples.
So, is diversity increasing or decreasing? I’m not getting into that.
Jeremy: The easiest way of `not getting into that’ is to look at `nature’ and ask ourselves under what conditions does diversity matter. Unstressed conditions – lots of moisture, sunlight, warmth, enough nutrients to be shared out – gives lots of species diversity as in tropical forests and seas; stressed condition – cold, dry, salty, seasonally flooded, oligotrophic, disturbed – gives low biotic diversity and natural monodominance. Arable farming is imposed stress on everything but the crop and (some) below-ground biodiversity. The result is crop monocultures that mimic monodominance in nature (perhaps the same for cows and sheep as mimics of natural herds). The recent promotion of agroecology does not understand the `culture’ bit of agriculture: the need to till fields and sow seed to reduce the bad bits of agrobiodiversity. Ecologist have noted the `paradox of the plankton’ – why so many species in an apparently uniform environment? The paradox of diversity to me is Phragmites australis – masses of monodominance in wetlands all over the place. How does it manage?
Tabarrok makes a good point, but his claim that “trade… is welfare enhancing” isn’t entirely convincing. The decreasing local and global diversity of cultivars grown (in his model) increases risks of occasional widespread crop failures, perhaps outweighing average-year increases in consumer choice.