Arthur Schopenhauer, On Ethics
, from Parerga and Paralipomena
(tr. R.J. Hollingdale):
The question has been raised what two men who have grown up entirely alone in the desert would do when they met one another for the first time. Hobbes, Pufendorf and Rousseau have given quite different answers to this question. Pufendorf believed they would approach one another affectionately; Hobbes, that they would be hostile; Rousseau, that they would pass one another by in silence.
Cf. Isaac Bashevis Singer, Enemies: A Love Story
(New York: Farrar, Straus and Giroux, 1972), p. 38:
The last two people on earth will kill each other.