Copyright 2001, Environmental News Network
September 27, 2001
By David Suzuki

With 6 billion people consuming the world's resources at a phenomenal rate, human impacts on our environment are often immediate and obvious. But the changes aren't merely physical. Amazingly, humans have also become the world's greatest evolutionary force.

Evolution through natural selection is the process by which successful traits are passed on from one generation to the next. We tend to think of evolution as an entirely natural phenomenon, driven largely by geographical and biological pressures.

That may be true in a pristine environment, but few, if any, environments on Earth can be considered pristine today. Instead, we live in a world where virtually nothing is free of human influence. And a recent analysis in the journal Science argues that humans now drive evolutionary change — and it's costing us immensely.

The toll is enormous because the fields where humanity has the greatest influence on evolution also affect our lives most directly: fields like health care and food production.

Conventional farming, for example, uses vast quantities of chemical herbicides and insecticides to reduce damage to food crops from pests. But these chemicals do not kill all of the pests, and those that survive pass their genes conferring resistance on to the next generation. Using the same chemical again and again ensures that each subsequent generation of pest will be less and less susceptible to the chemical's effects. In this way, we speed up the evolutionary process, and as a result, insects and plants often develop resistance to a pesticide or herbicide within 10 years of its deployment.

In the United States alone, farmers use about 300 million kilograms of pesticides every year. Yet in spite of this huge effort, 10 to 35 percent of American crops are still lost due to damage from pests, costing the industry billions of dollars. Researchers say that some of that loss is no doubt due to evolved resistance, which pushes the need for new chemicals. But developing each new pesticide costs about $80 million, takes time, and once deployed, can have toxic side effects on other organisms.

In health care, humanity's acceleration of evolution is even more troubling. The development of antibiotics has saved the lives of millions who might otherwise have succumbed to bacterial infections. But bacteria, like insects, can evolve resistance to the drugs we use to kill them. For example, common bacterial agents like Staphylococcus aureus are now resistant to penicillin, and up to 50 percent are resistant to stronger drugs.

Like bacteria, viruses also develop resistance to our drugs. HIV, the virus that causes AIDS, for example, rapidly evolves to resist antiviral therapies. That's why drug cocktails, which attack the HIV virus in several different ways, have become common. These cocktails greatly slow the virus' ability to replicate and thus reduce the speed of its evolution. Unfortunately, the use of such cocktails is limited by their toxicity to humans.

In many cases, human misuse of drugs can be blamed for at least some of the rapid evolution of resistance. Antibiotics, for example, sometimes are not properly administered, or the course of treatment is cut short, leaving resistant bacteria to multiply. They are also often prescribed to "treat" illnesses over which they can have no effect, such as colds or the flu. And they are routinely used to promote growth in livestock, an activity known to increase antibiotic resistance.

A more integrated approach is needed to slow the evolution of pests and pathogens. A recent study in the Journal of Applied Ecology, for example, found that farmers can enhance weed suppression in wheat fields by planting evenly distributed crops in higher densities. Other studies have found that planting a diversity of crops can reduce the need for herbicides and pesticides. To reduce bacterial evolution, the use of antibiotics to increase growth must end and antibiotic treatments must be more closely monitored.

Having to constantly develop new chemicals and drugs to fight stronger and stronger pests will always leave us one step behind. Instead, we must use all the cross-disciplinary resources at our disposal to create an integrated strategy that will keep human-accelerated evolution to a minimum. Error: Unable to read footer file.