Sex among the Oankali is complicated and becomes more so when humans become involved. Children are born in pairs, and are always planned and wanted. Children choose their own sex, gradually, as they mature, and tend to become the sex of the parent with whom they spend the most time. Actually, when you come to think of it, this isn't such a bad idea, especially for the one in 100 children in the US today born with ambiguous genitalia. Well, quite a few, given our rates of divorce and remarriage.
Some children can point to a dozen grandparents.
In my opinion, only a woman could have written these books. There are no machines whatsoever, anywhere. Transport is by snail-like animals called tilios. Houses and rooms are organically grown, with shapes and spaces that can be changed at will. Everyone is superbly nourished on vegetarian, genetically-engineered, food.