Wednesday, June 9, 2010

Evolutionary Diversity

My recently-released Green Planet: How Plants Keep the Earth Alive describes many of the things that plants do that make all of life possible. It is obvious, then, that we need to save them. But many plants do not need any help from us. They are already abundant and will keep growing even after the human economy and human population collapse. Trees will someday grow over all of our decomposing human structures. Why, then, do we need to save plants, which seem capable of taking care of themselves?

That is, evolution has produced a tremendous diversity of organisms, most of which seem useless to us. Usefulness to us is no adequate basis for measuring a species’ value. But as it turns out, many of the products of evolution are useful to humans in surprising ways.

It is not just plants that the world needs, but a diversity of plants. We need not just the abundant species, but the rare ones also. And it is the rare ones that are vanishing due to human activity. Many rainforest plant species are becoming extinct because of the destruction of the habitats in which they live. And if we do succeed in saving the habitats, we might only discover that global warming will cause these habitats to be unsuitable for the very species for which we have saved them. We also need to save genetic diversity that is within the populations of each plant species.

What do we need the rare species of plants for? Many wild plants have already proven to be the source of pharmaceutical compounds, and of genes that have been used to protect our agricultural crops from diseases. And here is the point. We cannot know in advance which plant species may prove important to us, and which may not. Who could ever have guessed that chemicals from a little species of pink-flowered plant from Madagascar would contain a drug that saves children from leukemia? or that the Pacific yew would contain a chemical that helps to cure ovarian cancer? We cannot save only the important species; we have to save all of them, since we cannot know which ones of them are important to the human economy.

When a rare species of plant becomes extinct, the world loses only a tiny bit of its capacity to produce oxygen, absorb carbon dioxide, hold down the soil, and contribute to the food chain. A tiny loss? But with this species is lost a treasure of genes, some of which just might be of immense importance to the human species.

A different version of this essay will appear on my website.

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