Complicating their task is the fact that many characteristics of a given species vary from male to female or adults to juveniles.

If it cannot find a partner, the worm doubles up so that its female bits and male bits can go to town.

Male-female worm pairing of schistosome, one special biological phenomenon of the life cycle, is of vital significance to its reproductive function.

In some, the Y genes seem to override expression of X genes even if there is only one Y and several X chromosomes, and the polyploids remain dioecious.

The combined effects of male-male pairing and poor performance by male-female pairs could be severe.