It's not human nature.
Give a 1 year-old a ball. He plays with it, then hands it back to you. Of course, he wants it back because he knows innately what is important: sharing.
Virtually all toddlers I've seen or read about exhibit this behavior.
UNTIL they hear mommy and daddy say, "Don't go in there! That's OUR room. You stay in YOUR room; Don't touch that! That's your brother's! You play with YOUR toys,", etc.
The seeds of the concept of private ownership and (gack!) its "inherent value" are sown very early in the human existence.
