William D. Nordhaus:
Since it is intelligence that distinguishes our species and inventiveness that has determined our history, by what standard should an unconventional act or attitude be called unnatural? How can human nature be held to another standard of naturalness than its own? Perhaps with our intelligence comes the capacity to know about and empathize with the problems of strangers, and this makes it natural for us to do so. On grounds of their intellectual and practical limitations, bears in Canada must be forgiven their apparent indifference to the fate of bears in China. Under other conditions -- bigger brains, opposable thumbs, bipedalism -- for all we know they might be model activists.
My point is that our civilization has recently chosen to identify itself with a wildly oversimple model of human nature and behavior and then is stymied or infuriated by evidence that the models don't fit. And the true believers in these models seem often to be hardened in their belief by this evidence, perhaps in part because of the powerfully annealing effects of rage and indignation. Sophisticated as we sometimes claim to be, we have by no means evolved beyond this tendency, are deeply mired in it at this very moment, and seem at a loss to think our way out of it.