Hume describes (E, 235) as a fancied monster a man who has no manner of concern to his fellow-creatures but to regard the happiness and misery of all sensible beings with greater indifference than even two contiguous shades of the same color (ibid.). To limit one's concern to those sensible beings who are of one's own species is to be part-monster, but such monsters, alas, are not merely fancied ones.

p. 75 - Knowing Our Place in the Animal World