The biological meaning of species


  • *This paper is based on lectures given in the University of Cambridge (the Hans Gadow Lecture) and at Imperial College (a University of London Special Lecture) by the author in October 1968.


The two medieval species concepts, the essentialist and the nominalist, have been replaced by the biological species concept, denned in terms of the relation (i.e. ‘reproductively isolated’) between populations. The species represents an important level in the hierarchy of biological entities from the molecule to the community. Six major areas are discussed, on which much of the research on species is now focused.