Saturday, January 26, 2008

Genetic variation & cattle   posted by Razib @ 1/26/2008 09:41:00 PM

The New York Times Magazine has a long piece about replacement of Uganda's native Ankole breed with Holsteins:
"You know, in Uganda, we have to look for survival of the fittest," Mugira said once he finished sorting out the confusion. "These ones, they are the fittest," he went on to say, gesturing toward his Holsteins. In physical terms, there was really no contest between the tough Ankoles and the fussy foreign cattle, which were always hungry and often sick. But the foreigners possessed arguably the single most important adaptive trait for livestock: they made money. Holsteins are lactating behemoths. In an African setting, a good one can produce 20 or 30 times as much milk as an Ankole.

Who could complain about over an order of magnitude increase in productivity? Well:

If the Ankole cattle are able to mount a comeback, it will be because circumstances have endowed them with a unique set of defenses, both evolutionary and political. Members of President Museveni's ethnic group populate the upper ranks of Uganda's government. Some prominent Bahima have started an organization devoted to preserving Ankoles, under the patronage of a one-eyed army general who spends his free time painting rapturous portraits of cows. One afternoon, at a pricey restaurant in Kampala, I had lunch with the organization's chairman, Samuel Mugasi. Dressed in a dapper gray suit and a French-cuffed pale blue shirt, he told me he was a civil servant and part-time rancher.

"They have tasted the money," Mugasi said of the farmers who switched to Holsteins. "They are excited about having these big earnings, and they are forgetting the cultural aspect."

A lot of people talk as if white tourists in Third World countries are special in the way that they bemoan the passing of quaint "traditions" which they had enjoyed "experiencing," but which the "natives" were happy to get rid of. But this sort of patronizing and instrumental attitude toward the unwashed is universal, it seems to be an attitude correlated with leisured status. Indian Americans and Irish Americans who visit their ancestral "homelands" over the years complain about the destruction of the cultural traditions, i.e, poverty, which made their earlier experiences more "authentic: (luckily for Indian Americans who want to get in touch with their "roots" most of India is still living in authentic squalor and deprivation!).

But there's a serious case to be made for preservation of extant genetic variation. The question I have is this: how many individuals of various breeds do you really need to keep around so that diversity is preserved for future utilization? In other words, I understand the logic of adaptive acceleration where large Ne is critical to the production of rare positive mutations; but don't we get to a point of diminishing returns for populations where we're more interested in modal alleles which might be disjoint across breeds? That is, the genetic traits from breed A you want to preserve in case they come in handy are common in breed A, so you don't need that many of breed A around to serve as a reservoir. I just don't see why we need maximal diversity, it seems the sort of variation which is encapsulated by species richness is more important here than proportionally weighted diversity indexes.

In any case, as alluded to in the article, maintaining relict populations of dying breeds like this seems like a public good which any prudent government can provide. But another issue with the article is that it doesn't seem like the author is a science writer, so he engages in the fallacy of blending genetics. For example:
...And something else is being obliterated: genes. Each time a farmer crossbreeds his Ankoles, a little of the country's stockpile of adaptive traits disappears. It isn't easy to measure genetic "dilution." What is evident, however, is that the Ankoles possess much worth saving. For instance, their horns, often seen as ornaments, actually disperse excess body heat.
I guess it's nice that he put quotes around dilution, but the rest of the article suggests to me that the author hasn't internalized that genetics is discrete, and that information isn't destroyed through cross-breeding. Rather, it seems that a good program of cross-breeding could result in a superior breeds of Holstein optimally suited to the local climate. That's what happened with indigenous African lineages as they hybridized with introduced South Asian ones 2,000 years ago to produce the Ankole according to the article! This sort of piece in a widely circulated publication such as The New York Times Magazine could have been a serious examination of agricultural and quantitative genetics, and just how much we depend on these unsexy sciences to feed the world. As it is, there's a lot of hand-waving scare-mongering....