Producing a more complicated definition with a special case for mammals vs. not mammals doesn't really add anything, even if it weren't for the platypus or the echidna being further examples of things not working like that.

Biology is messy, the boundaries are messy, the words we use are merely for our own benefit to simplify a messy and complex reality.

Messy edge cases doesn't mean let's just throw everything away.

I didn't ask you to throw anything away.

Someone forgot that the platypus exists.

The exception is not the rule.

Abstractions are useful, this is true, but the exceptions are a reminder that they are not reality, they are just a categorization we overlay on top of reality to help us understand it. Their utility is contextual.

Your abstraction ignores all the sterile men and women too, by the way. That's because it is a particularly bad one.

The fact of the matter is that if someone is missing a leg they are absolutely human but they are broken nonetheless.

That analogy illuminates nothing.

To be sterile is to be broken but it doesn't reduce ones humanity.

Nobody's suggesting that it might.

You're the one who wrote:

> Mammals on the other hand have males that impregnate the females.

We're all saying "that's not a very useful definition".

someone forgot the echidna exists