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For the vast majority of the history of our kind we were in some ways no more sophisticated than crows, which use sticks to poke around in promising holes. Eventually, of course, we discovered fire and invented stone tools, which then led to guns, pesticides and antibiotics. Using these tools, we encouraged the survival of favorable species such as wheat and yeast needed for beer and cows for meat and milk—a garden of delights.
But we also encouraged a garden of neglect—a surprising number of resilient pests that have been able to survive in spite of our weapons. These species are now coming back to haunt us as toxins, pathogens or worse. Here are ten ways we have helped this garden of neglect prosper.
1. SHARP ROCKS, SOFT FLESH. In the beginning someone held aloft a sharpened rock. "Progress!," he screamed out, or maybe, "Ouch!," depending on which end he grabbed. With that first stone weapon and its many pointy descendants, life changed. Our initial impact would have been small. However, by 10,000 years ago we had extinguished many of the largest species on Earth—mastodons, mammoths, American cheetahs, giant kangaroos and many more. In our wake, we left behind smaller species more able to reproduce rapidly or escape detection in the first place.
As humans came to rely on tools to survive, those with hands better able to make and wield those tools were more likely to pass their genes to the next generation. Mary Marzke at Arizona Sate University in Tempe argues that hand bones of humans are quite different from those of other primates because of our use of tools. Our hands are better able to manage the subtle grips necessary for making and using tools to maim or kill other species. In response to our first tools the animals around us changed. So did we.
2. BIG FISH, LITTLE FISH. Not only have we altered the course of big game evolution on land but we've also effectively reduced the size of fishes in the sea. Fishermen prefer to catch big fishes, and fishing regulations tend to prohibit the harvest of the smallest individuals of a species. In response, fishes have evolved the ability to reproduce at a smaller size and/or younger age. If they can breed before they get big enough to be harvested their genes stand a much higher chance of being passed on. American plaice, Atlantic cod, Atlantic herring, Atlantic salmon, brook trout, and chinook salmon all have appeared to grow more slowly and/or to reproduce at smaller sizes where and when they are heavily fished (Jorgenson et al., 2007; Palcovacs, 2011) Once, a large cod could eat a small boy. Now, a small boy could almost eat an entire cod.
3. RESISTANCE IS FUTILE. Bacteria have been evolving in response to threats from other species, including fungi, for hundreds of millions of years. Bacteria and fungi compete for food and often do so using chemical warfare. A fungus evolves an antibiotic and bacteria evolve resistance, so fungi evolve a new antibiotic. Recently, though, things changed. We invented (or rather stole from fungi) antibiotics, which allowed us to kill bacteria—and, importantly, treat bacterial infections. However, by using them too much, too incompletely or too indiscriminately we cause bacterial strains resistant to our drugs to evolve. Unlike fungi, we cannot retaliate by simply evolving new antibiotics. Hundreds of bacterial lineages have evolved resistance to more than a dozen of our antibiotics. In response, we are forced to discover new antibiotics, an endeavor that has proved ever more difficult.
4. GOING (ANTI)VIRAL. Viruses generally evolve even more quickly than bacteria. For example, multiple drugs for HIV infection are taken together as a cocktail for one reason: the HIV virus evolves quickly. The cocktail slows the evolution of full resistance. Even if HIV evolves resistance to one drug, the odds it will evolve complete resistance to all three are far lower. Similarly, the flu that usually starts each year in Asia is different by the time it reaches North America. The flu virus evolves to get by not only as a function of how we respond to it but also in response to our population size and patterns of movement. It, and other viruses, even evolve within our bodies. The virus that makes you sick is almost inevitably different than the one you give someone else.