Species, Concepts of

What are species? We take a historical approach to demonstrate how our understanding of the nature of species has changed since Darwin׳s time up till the current postgenomic era. If species are fundamental units of nature (like cells, or organisms, say), as some scientists believe, then their underlying basis has yet to be revealed. Instead, it seems more likely that the species rank in taxonomy is a man-made distinction; a heuristic cut-off that can perhaps be agreed upon by biologists to enable communication on issues of biodiversity, human health, agriculture, and conservation.