Monday, August 26, 2013

GM plants: when the evolutionary issues trump all others

We discussed GM technology and some of the debate about it on Friday.  Today we're addressing some other aspects of the debate that may not be as clear even to many of the disputants over the issues. These are issues that are relevant to things we often talk about here on MT.

Flavr Savr tomatoes engineered to delay ripening; Wikipedia
Why not GM?
There are numerous reasonable objections to genetic modification, some of which we touch on below.  We ignore the ill-informed reactions -- such as that tomatoes with a fish gene inserted will taste fishy, or that orange trees with a spinach gene will produce green fruit.

One objection is economic.  It is a resistance to the greedy monopoly of economic control of farming, and the exploitation of domestic and (especially) developing-world farmers.  It offends a sense of equity. 

Another source of resistance is epidemiological.  It is the distrust of the produce itself, such as that it might trigger unexpected toxic or allergic reactions. We always eat foreign proteins (we're not corn or chickens, after all), and unless we're allergic, we readily digest them, and reap their nutritional benefits.  Still there are concerns that some GMOs may engender reactions.  There have been various claims, few if any strongly as yet substantiated, for other sorts of effects (such as on fertility). 

A third is sociological, involving resistance to the displacement of more putatively sustainable multicrop, multispecies, mixed, smaller scale farms by huge monocropping.  For long-term sustainability, mixed crops save soil from runoff, require less fertilizer, fewer pesticides and are more natural.  Small, mixed farms are run by communities of local farmers, not itinerant workers, and so on. 

And, there is the evolutionary objection, which is related to the sociological objection.  The latter is in some ways the most scientifically inflammatory, or so it would seem.  It is this that is most relevant to MT and our personal interests in evolutionary genetics. The idea is that if you make a crop inedible, or make it resistant to pesticide, you put heavy selection pressure on pests, animal and plant, eventually favoring those with resistance mutations--and then you've got a real problem on your hands. Wild crops may gain transgenes through cross pollination (see Friday's post), and crop diversity, a major evolutionary asset, will be reduced. Further, as with antibiotic resistance, every herbicide or pesticide that can no longer be used is an economic jolt to farmers practicing conventional agriculture.  Evolutionary biologists opposing the Monsantoizing of the world point this out, and have done, in quite strong terms--and their warnings have been born out repeatedly.

However, this objection is not always warranted; again, not all GM is alike. Many GM changes should not have particular evolutionary implications. Transgenes that keep fruit from spoiling, or that affect its taste or color seem like examples. While such changes dramatically affect the plant or animal's reproductive fitness through the intense artificial selection that is agriculture, it's harder to envision these transgenes conferring a fitness advantage for related species if they escaped into the wild, such as is seen with pesticide or herbicide resistance.

The transgene would perhaps be more likely to have negative implications (just because it's a random gene tossed into the genomic mix of the recipient wild species). But most likely it would be selectively neutral--that is, it would have no effect on the recipient species reproductive chances.  In this case, the most likely fate of the transgene is to be lost just by chance--because this is the typical fate of any mutational change in any species.  But even if it persisted, it would have no implications for agriculture.

This seems to be the story of golden rice, with the transgenic modification to make vitamin A in rice, a potential boon to many underdeveloped countries where vitamin A deficiency is highly prevalent and rice is heavily the staple food.  A Sunday NY Times commentary discusses the issues.  The article doesn't describe the transgenic engineering that was done, but it does note that it's not a particularly strange modification, even for plants, it's developed by a non-profit institution, and the farmers can replant seeds they've grown.  So many of the ethical objections would seem to be avoided.  Still, there appear to be many reflex objections of a generic type.

Could something go awry with this plant, densely used in very widespread and global areas?  Any new gene could, in principle, interact somehow with local pests from bacteria to insects, and it is plausible in principle that some allergic or other reactions could occur.  However, this seems far less likely compared to GM species engineered in relation to strong selection involved with agents like antibiotics, pesticide and herbicide resistance.  So such objections do, at this point, seem rather a stretch, unless one is just nostalgic for some supposed good old days in agriculture.  After all, artificial selection has been tinkering with all our domesticates' genomes for millennia.  On the other hand, if someone really is pining for older ways, that's a legitimate viewpoint (even if it may ignore the real-world plight of our heavily populated globe).

Whatever one feels about GM plants, a productive debate can only happen if people actually understand the issues.  It is perfectly legitimate to object to economic, epidemiological, sociological, or evolutionary aspects of GM foods.  But many have opposite views, and are unconcerned about the industrialization aspects, for example (after all, many have jobs related to industrial ag).  In any case, it is not legitimate to mix issues.  That can't move the debate forward.

Whether GM crops are here to stay or will be displaced for either scientific or political reasons, only time will tell.  That there are very serious evolutionary issues is by now very clear indeed.  To many, they trump all the other issues.  In any case, while the epidemiological and sociopolitical sides of GM technology's impact are absolutely suitable for the policy arena, they are largely separate from the issues stemming from the evolutionary problems.

If the evolutionary issues prove to be intractable--if agribusiness can't keep one step ahead of natural selection, then we will eventually, maybe even rapidly, revert to other means of maintaining high global agricultural output.  If the problems can be addressed by big-science methods, then the overall economics--whether you like it or not--may well leave them in the driver's seat of future agriculture.  However the issues play out, billions of peoples' lives will be affected.


Jim Wood said...

As you point out, GM genes that "escape" into wild species are likely to be selected against or, at worst (from our point of view), to be selectively neutral. I think I might put it a bit more strongly. Artificial selection in crops (and in animal domesticates) is a continual struggle against natural selection, and crop plants that go "wild" seem very often to go through intense selective pressure against the very traits that humans selected for. So maybe selective neutrality is unlikely?

On the other hand, one can envision more troubling scenarios. There are weed species (in rice, oats, etc.) that are very closely related to the domesticates they exploit. If a GM gene for herbicide resistance were to get into one of those species, it could decimate this year's crop. Even supporters of GM need to contemplate the potential risks on a case-by-case basis.

Anyway, I salute you and Anne for the last two days' posts, which present one of the most balanced treatments of GMOs I've ever read.

Jim Wood said...

Point of clarification. When I said "If a GM gene for herbicide resistance were to get into one of these [weed] species, it could decimate this year's crop," I was assuming, of course, that the herbicide in question was used on this year's crop. Otherwise I would guess that the weed would be at a selective disadvantage.

MRR said...

While I have appreciated having a different take on GMOs through these posts, I must admit to being lost on what the point of this last post is.

If anything, I feel that it is being confused by the need to get to a conclusion about "GMOs".

Some GMOs produce insecticides, and suffer from problems associated to insecticide production, while others produce vitamin A, and do not.

Some GMOs are produced by big business, are patented, and are used in intensive agriculture, but none of this is evidently (as far as I understand) carried by the technique of genetic modification used.

I feel that the discussion would be clarified if there was an admission that GMOs are not really a thing, but a technique which can produce diverse things.

As a result of this confusion, the authors do not seem to be able to discuss Golden Rice without raising issues about Big Ag or monoculture. Which are distinct issues in my humble opinion.

Ken Weiss said...

That is what the rice paper is concerned with, I think--the spread of resistance to the related weeds

Ken Weiss said...

I am travelling and don't have easy access to references, but the idea about 'reversion to type' as it was called when domesticates were let loose and they returned to be more like the wild relatives as a major issue in the Victorian age.

Indeed, it was related to the title Wallace used in his 1858 Ternate manuscript on natural selection, that was read to the Linnaean Society along with Darwin's notes that introduced evolution.

Ken Weiss said...

I would not argue with your suggestion about clarification, but basically I would say that the issues related to GMOs are intertwined, not simple. People pick and choose evidence to defend their predilections, which they hold for whatever reason, selfish or otherwise.

But I think if we want any sense of clarity we need to disentangle the motivations and isolate particular issues. Spread to wild relatives, evolution of resistance, economic exploitation, and so on are such issues. They are related, but I think need to be recognized as not being identical.