ABSTRACT
A new species develops if a population which has become geographically isolated from its parental species acquires during its period of isolation characters which promote or guarantee reproductive isolation when the external barrier breaks down. Groups separated by geographical isolation are originally species only in posse. Their separation into good species is a subsequent process, accompanying the process of character divergence. A new species develops if a population which has become geographically isolated from its parental species acquires during its period of isolation characters which promote or guarantee reproductive isolation when the external barrier breaks down. Groups separated by geographical isolation are originally species only in posse. According to the definition of the Biological Species, sympatric speciation requires that a reproductive barrier be formed within a population. If the barrier is a result of mutation, it should be a rare event, and the chance of the same mutation in two individuals of opposite sex is remote.
