it's called the species problem in the philosophy of biology

The species problem is the set of questions that arises when biologists attempt to define what a species is. Such a definition is called a species concept; there are at least 26 recognized species concepts.[1] A species concept that works well for sexually reproducing organisms such as birds may be useless for species that reproduce asexually, such as bacteria

https://en.wikipedia.org/wiki/Species_concept