Evolutionary Arms Race

Human beings did not invent pesticides. Plants and fungi got there way before us. Humans in general have learned practically nothing from their experiences.

Consider the tobacco plant. Highly poisonous to insects, its presence in a garden, or its leaf extracts sprayed over an infestation, can keep crawly plant predators at bay. Or there are endophytic fungi, which intertwine their thread-like mycelial bodies all throughout the body of a plant alongside its cells, such that when predators attempt to eat the plant, they're repelled.

It used to be that plants were almost all inhospitable to animals. The older plant families, your ferns, cycads, horsetails, these are plants that are either poisonous outright or contain very little in the way of animal nutrition. (And for the purposes of discussion, it should be remembered that insects, spiders and worms, etc., are also animals.) Then a fascinating thing happened - some plants evolved parts that were intended to be eaten by animals. You could also say that they started producing non-toxic, edible starches in quantities never before encountered.

The flowering plants - which includes all our major food crops, because the grain-bearing grasses are also flowering plants, really the vast majority of human food - took a major detour from previous plant strategies, which had been all about developing enough toxins to keep yourself from being eaten. When you can't run away, this is a significant problem. So before, plants would develop toxins, and animals would develop immunities, then the cycle would start all over again.

Flowering plants instead evolved strategies like making most of their body parts poisonous, but having very tasty pollen so that insects would help them mate instead of having to rely solely on wind or water dispersal. Or putting starchy, tasty, fleshy wrappers around their hard and toxic-laced seeds, so animals would eat the fruit on the one hand, but perform the very useful service of carrying their seeds far away on the other. Endless variety, endless mixes of the various survival strategies. Flowering plants went on to become the largest family of plants, even though they were the most recent to evolve.

There's a fairly obvious lesson in the story. Consider this, from Sandra Steingraber's 1997 book, "Living Downstream", p. 152:

... In 1950, fewer than 20 species of insects showed signs of pesticide resistance. By 1960, Rachel Carson had documented an alarming 137 species resistant to at least one pesticide and urged that we should hear in this statistic the early rumblings of an avalanche. She was right. By 1990, the number of pesticide-resistant insect and mite species stood an 504.

In creating pests impervious to the arsenal of chemical weapons directed at them, the story of herbicides reiterates the story of insecticides. Herbicide-resistant weeds are not mentioned in Silent Spring, as they did not yet exist. Today, weed scientists have identified 273 such species. In tracing the explosion of herbicide resistance among weed species that began in the late 1980s, researchers conducting a recent study were forced to conclude that the "short-term triumphs of new pest control technologies have carried with them the seeds long-term failure." ...

Evolution doesn't work like this out of intent, obviously, even though it makes it easier to talk about it to speak as though that were true. This response to survival pressure over time is simply how species of living things are affected by their environment - the ones left standing by the latest catastrophe have more offspring and dominate the genetic makeup of the next generation. For insects, and many plants, whose lives are so much shorter than our own, this happens very fast.

So the long term effects of a strategy of total war against pests on our part have been the creation of ever greater numbers of pests resistant to our best weapons. Clever, clever us.

(Photo credit: Natasha Chart)