If the productivity of farmers has risen substantially over time because of technological progress, and workers can move freely between being farmers and barbers, the neoclassical theory of distribution predicts that the real wage(s) of:
both barbers and farmers should have risen over time.
farmers should have risen while the real wage of barbers should have remained constant.
barbers should have risen while the real wage of farmers should have remained constant.
both barbers and farmers should have remained constant over time.