The 'sixth extinction'
Biodiversity is the variety of species, populations within species, and genetic diversity within species. The biological diversity of the planet is being rapidly depleted as a direct and indirect consequence of human actions. An unknown but large number of species are already extinct, while many others have reduced population sizes that put them at risk. Many species now require benign human intervention to improve their management and ensure their survival. The scale of the problem is enormous. The current extinction problem has been called the 'sixth extinction', as its magnitude compares with that of the other five mass extinctions revealed in the geological record. Extinction is a natural part of the evolutionary process. For example, the mass extinction at the end of Cretaceous 65 million years ago eliminated much of the previous flora and fauna, including the dinosaurs. However, this extinction made way for proliferation of the mammals and flowering angiosperm plants. The sixth extinction is different. Species are being lost at a rate that far outruns the origin of new species. Conservation genetics, like all components of conservation biology, is motivated by the need to reduce current rates of extinction and to preserve biodiversity.

Why conserve biodiversity?
Humans derive many direct and indirect benefits from the living world. Thus, we have a stake in conserving biodiversity for the resources we use, for the ecosystem services it provides for us, for the pleasure we derive from living organisms and for ethical reasons. Bioresources include all of our food, many pharmaceutical drugs, clothing fibres (wool and cotton), rubber and timber for housing and construction, etc. Their value is many billions of dollars annually. For example, R. B. Primack suggests in his book Essentials of Conservation Biology (1998) that about 25 percent of all pharmaceutical prescriptions in the USA contain active ingredients derived from plants. Further, in 'Natural history at the cutting edge' (Ecol. Econ. 13, 1995, pp. 93-97), A. J. Beattie shows that the natural world contains many potentially useful novel resources. For example, ants contain novel antibiotics that are being investigated for use in human medicine, spider silk may provide the basis for light high-tensile fibres that are stronger weight-for-weight than steel, etc.