ECOSCIENCE

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Paul Ehrlich (Bring Professor of Population Studies and Professor of Biological Sciences, Stanford university) and Anne Ehrlich (Senior Research Associate, Department of Biological Sciences, Stanford) are familiar names to ecologists and environmentalists everywhere. As well they should be. Because it was Paul and Anne who — through their writing and research — gave special meaning to the words "population", "resources", and "environment" in the late 1960's. (They also coined the term coevolution, and did a lot to make ecology the household word it is today.) But while most folks are aware of the Ehrlichs' popular writing in the areas of ecology and overpopulation (most of us—for instance—have read Paul's book The Population Bomb) . . . far too few people have any idea of how deeply the Ehrlichs are involved in ecological research (research of the type that tends to be published only in technical journals and college textbooks). That's why it pleases us to be able to present—on a regular basis-the following semi-technical column by authors/ecologists/educators Anne and Paul Ehrlich.

THE GENETIC VULNERABILITY OF CROPS

Sometimes the most serious ecological challenges are also among the most subtle . . . and it can be difficult to alert people to the dangers of a problem when there's little visible evidence that a crisis exists. Such is the case with a situation that's currently posing a major threat to humanity's ability to remain in the business of high-yield agriculture.

Last year's record crops in the United States, and the success of the "Green Revolution" in many parts of the world, are thought by some to result solely from the application of modern pesticides and fertilizers. In truth, though, much of that productivity is due to the work of plant geneticists.

Applying Darwinism to crops, these scientists have carefully selected varieties that have characteristics valuable to farmers: high productivity . . . suitability for different climates . . . attractive flavors, textures, and colors . . . useful shapes . . . sensitivity to fertilizers . . . resistance to pests . . . and so on.

The basic resource that permits such artificial selection to be carried out is genetic variability. . . that is, a wide diversity of genes must be available so that plants with many different genetic makeup's (genomes) can be produced by crossbreeding. Geneticists then select, as parents for each generation, the plants that have the most desirable characteristics.

Gradually, through a process of creating arrays of new combinations and winnowing them by selection, the desired result is usually achieved . . . be it a cubical tomato that ships well (although it may be all but flavorless) or a variety of wheat resistant to a given strain of rust (a fungus that is the major enemy of that crop).

The need for genetic diversity becomes especially obvious when one considers the area of pest resistance. Plants have been attacked by insects, fungi, and other enemies for hundreds of millions of years. Quite naturally, many of them have evolved ways to protect themselves against such invasions. The spines found on cacti are an obvious example, but the most common (and potent) defenses are poisonous chemicals within the plants themselves.

Needless to say, the enemies of our crops have, over the years, evolved better and better ways to get around such chemical warfare . . . and the plants, in turn, have found ways of beefing up their defenses. The result has been a series of coevolutionary races, in which attack and defense mechanisms evolve—one after the other—in response to one another (see "Coevolution and Pest Control", MOTHER NO. 50, page 148).

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