This concept was acknowledged in the later half of the nineteenth-century once Darwins Origin of Species was published in 1859. Because of a failure to distinguish grouping from ranking criteria and because of an unwarranted emphasis on the importance of interbreeding as a universal causal factor controlling evolutionary diversifi-cation. Biological Species Concept Understanding Evolution Moreover to include the species not considered under the biological species concept this process was formed. . Nevertheless in palaeontology as in neontology as animals and plants are subjected to a more intensive study it is becoming increasingly difficult to make the concept of species fit the facts of nature. American Association for the Advancement of Science. The biological species concept BSC has served as the basis for defining species for over 75 years. 8 10 Endless time and effort can be expended on discussing the species concept