Humanity would then have to wait millions of years for natural evolution to replace what was lost in a single century. For practical reasons, if nothing else. Humanity's food supply comes from a dangerously narrow sliver of biodiversity. Throughout history, people have cultivated or gathered 7,000 plant species for food. Tens of thousands of species of the world's still surviving flora can be bred or provide genes to increase production in deserts, saline flats and other marginal habitats.
Natural pharmaceuticals offered by biodiversity are also underutilized.
Only a few hundred wild species have served to stock our antibiotics, anticancer agents, pain killers and blood thinners. The reason is to be found in the principles of evolutionary biology. Caught in an endless arms race, these species have devised myriad ways to combat microbes and cancer-causing runaway cells. We have scarcely begun to consult them for the experience stored in their genes. If the future enhancement of agriculture and medicine is not thought enough to merit conservation, then consider survival.