51:5.7

But while the pure-line children of a planetary Garden of Eden can bestow themselves upon the superior members of the evolutionary races and thereby upstep the biologic level of mankind, it would not prove beneficial for the higher strains of Urantia mortals to mate with the lower races; such an unwise procedure would jeopardize all civilization on your world. Having failed to achieve race harmonization by the Adamic technique, you must now work out your planetary problem of race improvement by other and largely human methods of adaptation and control.