The case of the mutant tomatoes

So the growing of food not only keeps humans alive, but it also contributes to the degradation of the land. That’s too bad. But what’s the connection with biological diversity?

Plants and animals must have genetic diversity in order to keep surviving and reproducing successive generations. The reason for this is that plants and animals are constantly under “attack” by other forces — bugs and diseases are the most important ones. (There are quote marks around “attack” because, while the plants and animals may perceive what’s happening as an attack, to the bugs and diseases it’s just making a living as usual. Humans “attack” a bowl of rice or cornflakes and call it eating; the tiny insects and diseases that get their food from human blood or the leaves of rice and maize plants, if they could speak and reason like humans, would probably call it the same thing.)

What keeps the rice plants (and corn, potato, and banana plants) from being eaten out of existence? It’s genetic diversity.

Take tomatoes, for example. All tomatoes are not alike. Different varieties of the same basic fruit contain different mixtures of genes, the basic units of heredity in both plants and animals. Sometimes these differences are the result of the plant’s adaptation to the environment in which it grows (a tomato that grows high up in the Andes may need protection against cold and longer periods of dryness, while one that grows in Canada’s province of Ontario may do best with plenty of rain and a longer growing period).

Sometimes the differences are caused by mutations in the set of cells that make up a plant. These mutations, which actualy are variations or changes in the organism’s usual cell arangement, may be harmful for the organism — may be so harmful that the organism cannot survive. But sometimes the mutations are beneficial. They may give a plant or animal protection against a disease, for instance. These mutations may be passed on to the organism’s offspring, and then the offsprings’ offspring. Gradually, through the process of adaptation to environment, or what some people call “evolution” and others call “the survival of the fittest,” a new form of the organism may emerge.

So if, for instance, quite by accident a tomato plant develops a greater tolerance for drought, those mutations may form the basis of a whole new variety of plant.

A bad rap.
Unfortunately, most people are taught to think of mutations as bad things. They think of bad science fiction movies with giant mutant houseflies or spiders that are big and nasty enough to consume entire cities. But “mutation,” in discussions of biological diversity, are not bad things at all. Mutations go on all the time in Earth’s organisms, including the ones that call themselves humans.

All these differences in the genetic makeup of the plants and animals that we use as our food serve as a sort of protection for the plant or animal. Why?

Not all tomatoes are alike, especially the one above that has been manipulated in the computer.

Well, suppose that all tomatoes were precisely the same, with identical patterns of genes. Not only would they all be the same color (and possibly taste very much the same), but they would all be wide open to attack by insects and diseases. A disease or bug that feeds on one tomato in a field, or even in a region, would be able to feed on all the others, as well, and could quickly spread across huge areas..

But if there were genetic diversity among the tomatoes — that is, if some tomatoes had their genes arranged one way, and other tomatoes had theirs arranged differently — the attacker would have a harder time. An insect that had no trouble gorging itself on Tomato A might discover that Tomato B’s genes produced a substance that was harmless to humans but poisonous to the insect. Science and farmers have long known that the best protection against massive crop failures is to grow a diversity of plants. Much, if not most, of agricultural research is devoted to figuring out ways to take advantage of genetic diversity in the foods we eat.

Scientists and farmers who need reminders of this need only recall two of the many dramatic examples of what can happen if diversity is missing. They involved two of the foods we prize most highly: maize (corn) and potatoes.

There is another threat to agricultural biodiversity, as well. In addition to crawling, creeping bugs that like to chew holes in apples and cabbage and most everything else, and viruses that suck the chlorophyll from the leaves of growing plants, leaving them frail and dying, there are people. The sort of lives we lead constitute a grave threat — perhaps the biggest threat of all — to the food we depend on for life.

The corn and potato disasters.