Mechanisms of seasonal cycles of behavior.

ULTIMATE AND PROXIMATE FACTORS UNDERLYING SEASONALITY ......... 81 NEUROENDOCRINE MECHANISMS UNDERLYING SEASONALITY ................ 83 Activational Mechanisms ........................................................................ 83 Timing Mechanisms .............................................................................. 94 HUMAN SEASONALITY .......................................................................... 98 Population Data ................................................................................... 98 Seasonal Affective Disorder ..................................................................... 98 CONCLUSIONS ....................................................................................... 102