Answer:
they are able to produce fertile offspring
Explanation:
A species is a group of organisms that are able to produce fertile offspring. This criterion is the basis of the biological concept of species proposed by Mayr in 1970, who defined a species as a group of genetically similar interfertile populations which are reproductively isolated from other groups. In consequence, only those populations whose individuals can interbreed (mate) with one another to produce viable and fertile offspring must be considered to be part of the same species.
