Us humans certainly prefer to put boundaries and names on things. And indeed, it is often unwise i.e. with (one of our) species definitions: A can procreate with B, B can with C but A cannot with C, meaning A==B, B==C but A!=C, a paradox because of our tendencies. Could it be a cultural thing? While I grow older I find it more natural to think of things as continuous or to assign uncertainty to "facts", but perhaps o…
If A is a male, B is a female, C is a male, your operator definition is even troublesome within a species.
What kind of mathematical object comes closer to this abstraction of a species? Maybe it's not about names and boundaries, but about getting to understand things for which you need abstractions.
I always appreciate when people do not fuss about definitions and easily change them but reason consistently after indicating their interpretation of those concepts.