Even in purely economic terms, the opportunity costs of extinction are going to prove enormous. Research on just small numbers of wild species has yielded major advances in the quality of human life — an abundance of pharmaceuticals, new biotechnology, and advances in agriculture. If there were no fungi of the right kind, there would be no antibiotics. Without wild plants with edible stems, fruit and seeds available for selective breeding, there would be no cities, and no civilization. No wolves, no dogs. No wild fowl, no chickens. No horses and camelids, no overland journeys except by hand-pulled vehicles and backpacks. No forests to purify water and pay it out gradually, no agriculture except with less productive dryland crops. No wild vegetation and phytoplankton, not enough air to breathe. Without nature, finally, no people.
Edward O. Wilson