Biodiversity is a word that has been mentioned widely since the mid-1980's, and yet surveys indicate that few Americans understand what it is. Nonetheless, we all have an idea that it deserves our protection and is at serious risk. The basic units of biodiversity are the species.
Species are the different kinds of organisms.
They are grouped in genera, and designated by two-part Latin names such as Homo sapiens, or wise human, the name of our own species. We are the only living species of our genus, Homo, though at least two other species existed in the past. On the other hand, there are dozens of species of the oak genus, Quercus in the United States, as different as the California live oak, Quercus agrifolia, and the eastern white oak, Quercus alba. Species are not generally capable of interbreeding, or the hybrids between them are sterile, or only rarely formed in nature, whereas the individuals of a given species can, of course, cross sucecessfully with one another and produce fertile progeny. Most species consist of individuals that differ from one another genetically, depending on the conditions under which they have grown.