Can We Feed an Expanded Population?

One argument you often see is that our farmland can easily feed even more people and that our technology will see that famines are a thing of the past. I am going to suggest that this may be an overenthusiastic view of our ability. First, the world is losing a surprising amount of good soil every year, to water and wind erosion. Seawater rising will remove a lot of prime agricultural land, but there is a much worse problem that needs attention. The 18th May edition of Science had some information that might give cause to rethink any optimistic view. Our high intensity agriculture depends on keeping pests, weeds and fungi at bay, and much of that currently depends on the heavy use of certain chemicals. The problem is what we are trying to keep at bay are gradually evolving resistance to our agents.

Looking at fungicides first, there are basically four classes of fungicides licensed for use, and some of these, such as the azoles, have a number of variations, but the variations tend to be those to differentiate the compounds from someone else’s, and to get around patents. The fundamental activity usually comes from one chemical group. As an example from antibiotics, there are a large number of variation on penicillin, but they all have beta lactams, and it is the beta lactams that give the functionality, so when bugs evolve that can tolerate beta lactams, the whole set of such penicillin-like drugs becomes ineffective. For fungi, the industrial scale production of single crops in some regions optimises the chance of a fungus developing a resistance, and there appears to be the possibility of gene transfer between fungi.

This has some other downstream issues. Thus medical advances lead to people having a much better chance of survival through cancer treatments, but they then become more susceptible to fungi. Apparently Candida auris is now resistant to all clinical antifungals, and is a worse threat in hospitals because it can survive most standard decontamination procedures. A number of other fungi are very threatening in clinical situations.

So what can be done about fungi? Obviously, seeking new antifungals is desirable, but this is a slow process because before letting such new chemicals out into the environment, we have to be confident that there will really be benefits and the chemicals are sufficiently effective under all circumstances, and we also need to know there are no unintended consequences.

Insecticides and herbicides (and following the article in Science, these will be collectively termed pesticides) have the same problem. It was estimated that even now the evolution of such resistance costs billions of dollars in the US. With regard to weeds, in 1996 plants were produced that were not harmed by glyphosate, and the effectiveness of this led to over 90% of US maize, soy and cotton being planted with such plants. (Some will recall the fact that some were bred so the plants did not produce viable seed, and further seed had to be purchased from the company that developed the plant.) Now there are at least forty serious weeds that have developed resistance to glyphosate. Plants have been engineered that are resistant to chemicals mimicking previous herbicides but the weeds are defeating that. Weed species have evolved to resist every known herbicide, and no herbicide has been developed with a new mode of action over the last thirty years.

In agriculture, it is easy to see how this situation could arise. When you spray a crop, not every part of every plant gets the same amount of spray. Some of what you don’t want will survive in places where the dose was less than enough. From the farmer’s point of view, this does not matter because enough of the pests have been dealt with that his return is not hurt by the few that survive. However, the fact that some always survive is just what evolution needs to develop life forms capable of resisting the chemicals.

So, what to do? Obviously, more effort is required, but here we meet some problems that might be intractable. Major companies have to invest large amounts of money to provide a possible solution, and they will only do so when there are likely to be guaranteed very large sales. However, to defeat resistance, it is most desirable to pulse agents, thus using agent A one year, agent B the next, and no repeat for a number of years. That maximises the chance of avoiding the generation of further resistance, but what company wants to participate in the sort of sales future? We could try natural procedures and live with the fact that yields are lower, but that implies we really do not want to eat that much more, which in turn suggests population growth needs to be curbed. Unfortunately, there are no easy answers.

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