1. division into two parts, kinds, etc.; subdivision into halves or pairs.
2. division into two mutually exclusive, opposed, or contradictory groups.
3. Botany . a mode of branching by constant forking, as in some stems, in veins of leaves, etc.
4. Astronomy . the phase of the moon or of an inferior planet when half of its disk is visible.
Mankind suffers from dichotomy
So much battle between the two official sexes
That a few alternatives have arisen, ready to conquer.