Sir

The moral imperative of saving species and protecting nature, as put forward by Douglas J. McCauley (“Selling out on nature” Nature 443, 27–28; 2006), must be weighed against the moral imperative of saving people. Typically, it is the poorest members of our world community who are most affected by efforts to protect nature, and who suffer the most when ecosystems are degraded.

The conservation debate cannot be reduced to a choice between protecting nature or making an extra million for a yacht or villa. If it were, then perhaps moral arguments alone would be enough to protect the environment. The reality is that poor people are deforesting vast areas of tropical forest for subsistence agriculture, members of indigenous tribes are killing endangered wildlife and out-of-work fishermen are converting mangrove forests to shrimp farms. Moreover, biodiversity is greatest in the very areas where human populations are most dense, most rapidly growing and most impoverished (R. P. Cincotta, J. Wisnewski and R. Engelman Nature 404, 990–992; 2000).

McCauley does not acknowledge that economic valuation of ecosystem services can provide the data and tools needed to make human well-being part of the design of conservation projects. Although win–win scenarios are hard to find, it is important that we take the care to quantify ecosystem services, so that those situations in which both humans and biodiversity benefit can be identified and promoted. Moreover, if fundamental economic concepts such as GNP could be reformulated to reflect ecosystem services, then nations might embark on policies that better protect their natural capital assets. The economic valuation of ecosystem services is simply a way of getting everyone's moral imperatives on the same page. It is a way of recognizing that conservation must be accomplished in a just and fair manner, in a way that does not pit the basic needs of humans against nature.

Attention to ecosystem services is not equivalent to venal worship of the dollar. Instead, it provides an entry into market incentives, government policies, better-designed conservation projects and a broader constituency for conservation that reaches beyond the affluent Western world. Conservationists who promote valuation of ecosystem services have no intention of selling out on nature — we just want to make sure it is correctly valued.