Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Friendship between relatives itself seems to include a variety of species, but all appear to derive from the affection of parent for child. For parents love their children as part of themselves, whereas children love their parents as the source of their being. Also parents know their offspring with more certainty than children know their parentage; and progenitor is more attached to progeny than progeny to progenitor, since that which springs from a thing belongs to the thing from which it springs—for instance, a tooth or hair or what not to its owner—whereas the thing it springs from does not belong to it at all, or only in a less degree. The affection of the parent exceeds that of the child in duration also; parents love their children as soon as they are born, children their parents only when time has elapsed and they have acquired understanding,¹ or at least perception.