WordNet (r) 3.0 (2006):

human nature
    n 1: the shared psychological attributes of humankind that are
         assumed to be shared by all human beings; "a great observer
         of human nature"

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "human nature":
   Adam, Hominidae, Homo sapiens, clay, fallen humanity, flesh,
   frailty, generation of man, genus Homo, hominid, homo,
   human equation, human family, human frailty, human race,
   human species, human weakness, humanity, humankind, humanness,
   le genre humain, man, mankind, mortal flesh, mortality, mortals,
   race of man, weakness