Today we call it biodiversity. One of its principal advocates was the Oxford ecologist Charles Elton, whose book “The Ecology of Invasions by Animals and Plants,” argued that simplifying landscapes with weedkillers, or planting single crop species over large areas made a recipe for disaster. The best defense from diseases, other species or natural catastrophes, he said, was to conserve as much biological variety as possible in the fields and hedges of the countryside to counterbalance any threat. In his book he called it the conservation of variety.

Elton’s approach not only inspired Rachel Carson to write “Silent Spring,” about the harm done by insecticides, it also resonated among scientists in the defense establishment. Fantasizing about environmental warfare in the early 1960s, NATO scientists tried to imagine which links in ecosystems were vulnerable to manipulation. Studies had recently shown radioactive fallout infiltrating reindeer meat, a crucial part of Eskimos’ diets. It was a revelation to think that such a connection in the food chain was now targetable. But the reverse was also true, and underscored Elton’s point: the complexity of an ecosystem made any particular “link” less important, making the system less vulnerable.

This was the lesson defense planners took to heart. They decided that a robust peacetime market economy provided variety, and thus security in peace and war. If nuclear war ever came, a decentralized, diversified society would be in better shape than a centrally planned one like the Soviet Union’s. The same logic applied to biological variety. That is why strategic stockpiles of Western nations during the cold war did not collect enormous stores of favorite foods but samples of the widest range of species imaginable.

In the face of natural disasters, such diversity seemed to be the West’s ace in the hole. The variety of agricultural products in the United States far outpaced those of the Soviet Union, and is a reason that C.I.A. analysts predicted in the 1980s that global climate change would cause more harm to Russia than to the United States.