Friday, April 7, 2017

Plants vs Zombies: The GMO Edition

I know. It's been a while... Things are a bit rough. I've written a few pieces over on Medium, if you want to check them out.

So, in this blog post, I wanted to write about "superweeds", what they are, how they're related to GMOs, and some misconceptions about them. The first thing to know is that "superweed" is not a scientific term. Searching through the NIH's database of scientific publications, I only found one paper with the term "superweed", and it's a commentary, not a research article. Yet "superweed" is a term used ALL the time on websites that lobby against GMOs, like this article entitled "Superweeds: A Frightening Reality" written by the "Just Label It" campaign. 

My understanding of the term and its use is that "superweed" describes weeds that don't get killed by herbicides. They don't grow faster or stronger than other weeds. They arise due to selective pressure from the herbicide. Spouse, don't freak out. I'm going to explain this to you in detail, using your favoritest of analogies: zombies.

Imagine that the zombie apocalypse takes places tomorrow and is caused by a virus. Imagine that 1% of the human population had some sort of mutation in their DNA that made them resistant to the virus. That means that only 1% of the human population would survive. It also means that 100% of surviving humans are resistant to the zombie virus. The surviving humans would mate with one another and from that point onward, all humans would have the mutation that makes them resistant to the zombie virus (assuming, of course, that humans wouldn't mate with zombies... That would make a crazy scifi movie...). You could say that the surviving humans are "superhumans". 

But did the zombie virus cause the mutation? No, it did not. The superhumans were there all along. The zombie virus placed pressure on the system, and the mutant humans were "selected" because they lived.

A mutation that's shared by 1% of humans is a relatively large number of people. Why would so many humans have it? Well, maybe it makes humans resist other viruses too and gives them some sort of advantage. Or maybe at some point throughout the course of our evolution, there was a similar virus that wiped out a good chunk of our population, and our ancestors (human or not) survived because of the mutation. But since there hasn't been a zombie virus since that ancient plague, we haven't really needed that mutation. With no selective pressure, it may be why most humans no longer have the mutation.

But let's assume that there has never been any pressure for this mutation to remain in our population. In that case, very, very, very few humans, if any at all, would have the mutation making them resistant to the zombie virus. It would be pure luck if a human had that particular mutation, since mutations happen randomly in our DNA.Given how our species reproduces, there would need to be two humans who won this genetic lottery at the same time in history and in close proximity of one another, so that they could mate and have superhuman offspring. Otherwise, humans would get wiped out.

Pretty unlikely, right? Still, the zombie virus did not cause the mutation. 

Now, if the zombie apocalypse were part of a plan of some evil mastermind, the villain's best chance of success would be to release two viruses into the environment at the same time: let's say a zombie virus and a flesh-eating virus. The odds of a single individual or population being resistant to both viruses would be extremely, extremely, rare. 

So, that's probably as far as I can take the zombie apocalypse analogy.

Weeds that are resistant to herbicides are bound to arise, even with the best of herbicides. The same is true of antibiotic resistant bacteria. Given enough time, they'll be found. If a herbicide is well designed, no existing weeds will be resistant to it (i.e, in our analogy, a good herbicide wouldn't leave 1% of weeds behind). This is tricky, because there are so many different weeds to combat. But, the herbicides don't cause the resistance. Neither do antibiotics. Resistant bugs and resistant weeds win the genetic lottery and thrive. Since bacteria don't need to mate, it's even easier for an antibiotic resistant bug to spread.

Weeds that evolve to become resistant to herbicides have existed WAY before GMOs, because we've been using herbicides in agriculture before GMOs were commercialized. There are even weeds that have evolved to look like crops, so that they can evade hand-weeding. It is for these reasons that farmers are encouraged to practice good management to control weeds. This means that they're encouraged to rotate crops, to use herbicides that impact the plant in different ways, and to use mechanical methods to kill weeds, too. And although we may not like it, using two different herbicides makes sense and ag companies are starting to introduce GMOs with the ability to resist two herbicides. The odds of getting a weed that is resistant to both herbicides is much less, but again, it's only a matter of time before one arises.

Glyphosate has been a pretty good herbicide in terms of the development of herbicide resistant weeds. But because it was used on so many acres of land, the odds of finding a weed that "won the genetic lottery" increased. Consequently, glyphosate-resistant weeds have been identified in many areas and are a problem for some farmers. 

The term "superweed", when used in the context of the GMO debate, evokes imagery of a weed that's about to take over the planet. As I highlighted at the beginning of this piece, you'll see references to superweeds all over anti-GMO websites. Herbicide resistant weeds are a problem in agriculture, but it's far from being unique to GMO crops. So ask yourself why such language is being used, and be aware if its because the website in question is trying to manipulate your emotions.

For more on this topic, I encourage you to read this 2-page summary on superweeds or to look at this website. And follow @wyoweeds and @LynnSosnoskie on twitter (can't stress this enough).

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