Q. Biological species concept?
A biological species as defined by Ernst Mayr are "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups". For example there are some species called sibling species that are reproductively isolated although they have extremely minute genetic differences. This definition assumes that a species cannot interbreed with other species due to a variety of isolating mechanisms that are behavioural, physiological, genetic, etc. Thus, according to the biological species concept, individuals within a species have a gene pool available for recombination through sexual reproduction within the group, and is not inhibited by pre - or post -mating reproductive isolation. The main criticism of this definition is that it applies only to organism (i.e. life forms) that have sexual reproduction, and ignores the fact that some times gene flow occurs between closely related, sympatric species (species whose geographical ranges overlap).
For example, significant gene exchange has happened between bison and bus (domestic cattle). Such occurrences violate the basic notion of the biological species concept. Nevertheless, this definition of a species continues to be widely used even today.