Some scientists, especially those who study evolution and the human brain, argue that something deeper than culture is at work. They suggest that millennia of human evolution have conditioned us to respond primarily to immediate dangers-the snap of a twig, the crack of a thunderbolt, the flood in the canyon, the hunger in our stomachs. This, they argue, is clouding human ability to adapt to a threat that, until recently, has been invisible.

"The human mental system is failing to comprehend the modern world," wrote Robert Ornstein and Paul Ehrlich in their 1989 book, New World New Mind. "The human nervous system, well matched to a world in which small, sharp changes were important but large gradual changes were not, is inadequate ... Our nervous system and our world are mismatched now ... Although we are evolving, our mental machinery will not change biologically in time to help us solve our problems."

Ornstein, an expert on brain research, and Ehrlich, the author and Stanford biologist, linked this limitation of human perception to the problem of climate change, which was then barely a speck on the global radar. "In the long run," they wrote prophetically, "CO2-induced warming would melt the polar ice caps, thus flooding many areas. Our old minds, however, don't have the capacity to recognize the threat of CO2 increase. After all, a squiggly line on a chart is hard to translate into a portent of catastrophe."

In the nature of human beings, Ornstein and Ehrlich suggested, action seems imprudent if the threat is distant, even if it is real and growing. "Cultures did not spontaneously develop the ability to deal with long-term trends," they wrote, "because they had no need to until very recently."

If this is true--if biology is destiny--what does it say about reason, and human will? If our biology is hard-wired to respond to the most immediate threats--not to catastrophic scenarios of sea-level rise pegged to, say, the year 2050--is there any way to act in protection of our grandchildren, and theirs?

Edward O. Wilson, the Harvard evolutionary biologist, once said that far-off catastrophes, engineered by our own species, are simply out of the range of human capacity for planning and action. "It doesn't matter that that evolutionary process may be leading an entire species to the precipice," he said. "There is nothing in the species to foresee what will be happening ten generations down the line, only what is happening at the moment." Human beings, he added, "have a hard time reasoning why they should care what might come about 100 years hence."

Considering the effects of our actions today on people in a distant future is not unheard of, of course. Environmental leaders and even a few politicians speak of this. Some native peoples say they think seven generations forward, and there are indications that this is because they learned from past mistakes. According to some Native American oral traditions, the original inhabitants of the continent underwent hardships of their own doing and adapted. "Certainly in Lakota oral history, we have narratives saying our conduct seriously threatened the natural world," oral historian Edward Valandra of the Rosebud Sioux reservation told me. "And we paid a price for that. We were admonished. We paid a price."

Wilson concurs: "A general trait of early people was to eat up everything they could get their hands on, and to become conservationist only when finally they realized that it was necessary for their survival."

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