Nature is indifferent to the fate of individuals. It cares not when tsetse flies assail us. It shows little pity for a shrieking baby rabbit in a cat's jaws, for a squirrel run over by a car, for a beached whale, or for a rat in a sinking ship. At the individual level, nature appears capricious and unforgiving.

But as soon as we advance from transient individuals to species, ecosystems, and the biosphere as a whole, anarchy is replaced by orderliness, senselessness gives way to harmony, and scattered strands are transformed into a finely-woven fabric. Here we shall only touch upon a few features of the most intricate fabric of them all: the biosphere.

Interdependence. The biosphere is marked by the absolute dependence of every creature on others. In nature's design, there is no such thing as self-sufficiency. The honey bee cannot exist without flowers. To reproduce, many flowering plants depend on the springtime visits of insects. If all the organisms which find our various body secretions so appetizing vanish, we shall, in short order, ingloriously suffocate in our own wastes.

Complexity and Unpredictability. Ecosystems are complex and, hence, often unpredictable. Any tinkering with them may have unforeseen consequences. This point is essential to any informed discussion of such global environmental issues as the greenhouse effect, and needs therefore to be explained and illustrated.

First, an explanation. Ecosystems are comprised of numerous living and nonliving elements. We are often ignorant of the existence of some of these elements, and only partially comprehend others. All these elements, in turn, form an intricate web of interconnections and feedbacks, a web which often eludes our grasp. As if this is not enough, we have also good reasons to suspect that ecosystems often behave chaotically+a change in one or another of their seemingly insignificant components may, in the long run, profoundly alter them.

Second, illustrations. Over the years, my students have given me some fascinating examples of the complexity and unpredictability of ecosystems, but here I shall resort to less anecdotal examples:

1. Cats and Flowering Plants. Charles Darwin describes "how plants and animals remote in the scale of nature are bound together by a web of complex interactions." To his surprise, Darwin found that the number of certain flowering plants in an English countryside depends on the number of cats. Now, it is easy enough to suppose that April showers bring May flowers, but how could cats raise the numbers of plants? It so happens that these particular plants are pollinated only by humble-bees (=bumble bees). And the "number of humble-bees in any district depends in a great measure upon the number of field-mice, which destroy their combs and nests." At this point, the last link in this causal chain should be obvious, for the number of mice in any given region depends on the number of cats. The cat and plant populations experience the same ups and downs: with more cats there are fewer mice, more pollinating humble bees, and more plants. Thus, even in this simplified four-species network, we encounter features which could hardly be deciphered in advance.

2. Grass and Sea Gulls. "Alongside the runway of a certain airfield, the grass was allowed to grow tall in order to discourage gulls, which it did. But starlings increased; one set of nuisance birds was replaced by another. Moreover, the tall grass encouraged field mice, which in turn attracted raptorial birds. The grass also encouraged earthworms, which then crawled out on the airstrip on rainy nights and attracted gulls!" (Scheffer, 1974, p. 172).

Now, both examples involve crude subsystems. It goes without saying that some features of the biosphere+which is comprised of millions of species and their environments+are vastly more complex and unpredictable.