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Evolutionary tradeoffs and drought-tolerant crops

The Union of Concerned Scientists recently sent me a link to a report arguing that "Genetic Engineering is not Solving Agriculture's Drought Problem." This is an issue I address in detail in my book on Darwinian Agriculture, which will be available at the upcoming Evolution Meetings in Ottawa and more widely by the end of July.

Briefly, my argument is that mutant plants with greater or less expression of existing genes must have arisen repeatedly over the course of evolution. Some of those mutants were presumably more drought-tolerant than their parents, while others were less drought-tolerant. If there were no disadvantages to a given drought-tolerance gene, then plants with that gene took over. Repeat this process of natural selection for millions of years, and there may be few remaining opportunities for further improvements that are both simple (i.e., achievable by the sort of mutations that arise reasonably often) and tradeoff-free (never having negative effects on fitness, at least in past environments). My book therefore raises doubts about increasing the expression of existing plant genes to improve drought tolerance.

This argument applies to conventional breeding, not just genetic engineering. Another key point is that some tradeoffs rejected by past natural selection may be acceptable in an agricultural context. In fact, accepting acceptable tradeoffs may often be the fastest route to progress.

It's not entirely clear, however, whether my concerns above apply to the particular transgenic crop discussed in the Union of Concerned Scientists report. Monsanto's "DroughtGard" corn (maize) contains a gene derived from bacteria. Does this gene result in a phenotype very different from any seen in the recent evolutionary history of corn? If so, then we can't assume that this approach to drought tolerance has been repeatedly rejected by past natural selection. It may never have been tested by natural selection. Rather than rejecting it on theoretical grounds, therefore, we would need actual field data to determine the advantages or disadvantages of this transgenic variety.

Of course, those data would need to come from independent tests, not run or paid for either by Monsanto or by one of their commercial competitors. Agricultural universities run such tests every year, comparing crop varieties developed by different companies and by public-sector plant breeders. I look forward to seeing how DroughtGard does in such tests.

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