Origin of Species

The biological species concept - a species is a population or agroup of populations that are reproductive isolated from all otherpopulations.Reproductive isolation - the inability to exchange geneticinformation. Two types of organism are reproductively isolatedif they lack the ability to mate and produce healthy fertileoffspring under natural conditions.Whether two organisms are reproductively isolated or not is oftendifficult to evaluate, most commonly because they live indifferent regions of the world. In such cases, their phenotypicsimilarity or differences, are commonly used as a criterion forplacing them in the same or different species.5