Plants are subject to a number of natural dangers through disease, adverse weather and insect depredations; man-made disasters such as pollution and excessively rapid development take their toll as well. The preservation of plant species and plant genetic diversity is a matter of scientific principle or aesthetics to some, others recognize plants as nature's pharmacy and plant-derived medicines continue to be discovered. Some plants belong in very important ecological chains, and without being crops themselves, their absence would affect such important natural activities as pollination, insect reduction by birds and soil conditioning.