The importance of preserving biodiversity extends beyond the discovery of new drugs to understanding how other species have dealt with medical problems we currently face.
There is no shortage of incurable diseases. Cancer, autoimmune disease, emerging viruses and parasites, degenerative pathologies like arthritis and Alzheimer's disease and over 2,000 hereditary diseases drive an US$11 billion National Institutes of Health budget to resolve the physiologic bases, to clone the genes and to move beyond symptomatic treatment for fatal and debilitating conditions that fill our hospitals.
O'Brien, Stephen J.. 1995. "Genomic Prospecting." Nature Medicine 1, (8): 724-744. http://nsuworks.nova.edu/cnso_bio_facarticles/707