THE SECOND QUESTION. “Many animals are obligately sexual. Why? This is in marked and striking contrast to the vast majority of microbial eukaryotes which are facultatively sexual, and happily capable of vegetative mitotic clonal reproduction interspersed with bouts of sexual reproduction. Why this is not so for humans, mice, rabbits, is an interesting conundrum.”
http://www.sciencedirect.com/science/article/pii/S1749461315000391