Nature, for the wisest purposes, has rendered, in most men, perhaps in all men, parental tenderness a much stronger affection than filial piety.
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“Such unnatural indifference, far from exciting our applause, would incur our highest disapprobation. Of those domestic affections, however, some are most apt to offend by their excess, and others by their defect. Nature, for the wisest purposes, has rendered, in most men, perhaps in all men, parental tenderness a much stronger affection than filial piety. The continuance and propagation of the species depend altogether upon the former, and not upon the latter. In ordinary cases, the existence and preservation of the child depend altogether upon the care of the parents.” source