The offspring of a horse and a donkey, a mule is a useful working animal but is entirely sterile and incapable of breeding. ... 76 years after Mayr published his definition.

The genetic conflict between parents and their offspring is a cornerstone of kin selection theory and the gene-centred view of evolution, but whether it actually occurs in natural systems remains ...

This means the first generation needs to produce offspring who will themselves reproduce. Females tend to reproduce regularly, but each female can only produce a certain number of offspring. Males, on ...