Self-awareness has been a central theme in philosophical and biological research since ancient times. In the temple of Apollo at Delphi, the exhortation "Know yourself" is inscribed in Greek, an invitation to men to understand their own finitude, to understand their limits. In "Latin in his Discourse on the Method," René Descarte wrote, "Ego cogito, ergo sum, sive existo" (I think, therefore I am, or I exist) to underline the fact that existence derives from our awareness as thinking beings capable of reflecting on ourselves.