Posted: 16 March 2001

A group of organisms that, because of close genetic and physical similiarities, can naturally mate with each other and produce viable offspring (individuals that can also produce naturally). Within species are often other levels of similiarity, including sub-species, varieties and breeding populations. Organisms that reproduce only through asexual means (such as micro-organisms that reproduce by diving or budding) are sometimes difficult to separate using the species concept.