[Doctor Stochastic]

Still, absent evolutionary theory (or another cladistic formulation), why do you believe that egg-layers (in general) are not mammals or vice-versa?

[Tribune7]

It's how the scientific/academic thinkers chose to categorize things a long time ago. Mammals are defined, among other things, as being those that carry then nurse their young. This organization, I think, helps us understand the world a little bit better.

[gore3000]

"Still, absent evolutionary theory (or another cladistic formulation), why do you believe that egg-layers (in general) are not mammals or vice-versa?

What a totally contorted statement and at total misrepresentation of what was said (that is why you did not post what you were responding to). Theory proves nothing, evidence proves everything. The relationship between mammary glands and live birth is an almost necessary relationship. Unlike egglayers, live bearing animals need to feed their young till they can feed themselves. It is certainly much more of a necessary connection than mammary glands and ear bones. Yet one is untrue and the other is true (so far as we know from living species). Which just comes to prove that theory proves nothing.