The Beak of the Finch: Chapter 18 Summary & Analysis

Martin Taylor, a researcher in the Grants’ subterranean lab at Princeton, receives huge shipments of moth specimens every day from all across the U.S.’s Cotton Belt. He grinds the moths up in a mortar and pestle to extract their DNA. Taylor is studying the moths because they have, over the years, developed a peculiar and stunning resistance to pesticides. The moths that were able to tolerate initial sprayings of DDT in the 1940s passed on their genes to their offspring—and now, no matter how big the dose of DDT, the moths are able to survive it. The moths have developed resistances to other pesticides, as well. The pesticides’ inability to kill the moths, which feed on cotton, is panicking farmers across the region. It’s also an example of “visible evolution.”

Other insects, too, are rapidly developing complete immunity to commercially available pesticides. Some insects have evolved chemical antidotes to pesticides, or ways of dodging the poison such as by letting a poison-afflicted appendage fall from their body. These evolutionary mechanisms can develop over the course of a single growing season, which also spans multiple generations of the insects.

By studying the moths’ DNA, Taylor is working to determine how, biologically, the insects are resisting—and what this might mean for other species with which they share DNA. The moth’s gene that allows it to resist the pesticide is the same gene that many pesticide-resistant flies have—which shows that these “fixed categories” of different species are not as fixed as certain people (cotton farmers, especially) would like to think.

“Resistance movements” like this one are happening throughout the natural world. After the arrival of antibiotics in western hospitals in the 1950s, antibiotic-resistant bacteria appeared within just a year. Now, antibiotic resistance is being termed a “global epidemic.” Bacteria like E. coli grow so rapidly that when dosed with an antibiotic, the few surviving cells in the colony are able to replace their lost numbers within a day or two. The insides of a human body, then, becomes a site of natural selection and evolution in progress.

Investigators have fully mapped the genetic sequences of many kinds of viruses—but the sequences of viruses are always changing. Viruses evolve at a mutation rate of about a million times the rate of the human body—the weapon of the virus, Weiner writes, “is variation itself.” And viruses are constantly evolving—they are “our only real competition for domination of the planet,” says one microbiologist. The harder we attack bacteria through antibiotics, viruses through therapeutics, or cancers through chemotherapy, the more ably these rapidly growing resistance cells evolve. In other words, “whenever we aim at a species point-blank […] we drive its evolution.”

Elephants in regions of Africa where poaching is common have begun to evolve to be tusk-less. In order to protect the resource that humanity is “point-blank” trying to take from them, they are evolving in a way that’s detrimental to their short-term well-being but essential to their long-term survival. The same kind of things are taking place in fisheries. Fish are becoming smaller, since bigger fish are the ones prized by fishermen and the consumers they sell to.

The moths are evolving at a rate faster than what Taylor can keep up with. But farmers are still trying to shoot at them “point-blank.” Ironically, the more preventative spraying these farmers do, the more capably they arm the evolving moths against their attacks. The more pressure humanity places on bacteria or moths or fish, the more we force them to evolve around that pressure. What humans call “control” is merely, to these organisms, a change that must be met, and a challenge to which they must rise.