To believe humans are inherently selfish creatures is to believe that a 300 years dead philosopher had a better grasp of our nature than the whole of modern science. An absurdity that borders on religious levels of non-logic. Why do you cling to this outdated Hobbesian notion in the face of the heaps of evidence I have laid out this very thread?
I don't recall ever making the assertion that humans are "inherently selfish creatures".
Humans operate on a broad spectrum of different levels of consciousness,
from the psychopathic to the saintly.
The difference between rational self-interest and "selfishness"
is the inclusion of others in one's thoughts and values. I was
about to say something about free trade falling under the umbrella
of rational self-interest, but the point would be moot if you don't
believe in the concept of ownership.