Why do we make number one and number two? Not all organisms eliminate this way… why do we?
What organisms?
Cuz we can’t do #3!
But seriously, we (along with most higher-order fauna) have
complex, highly specialized waste removal systems:
Post-metabolic liquid waste removal (#1)
and
Pre-metabolic solid waste removal (#2)
You also have Post-metabolic gas waste removal…breathing out carbon dioxide.
Biological science knows no other moreefficient system.
And occasionally a bit of methane.