The Andorian and Aenar species are unusual in that there are four distinct Andorian and Aenar sexes, and a union between all four sexes, an act known as the shelthreth, is required for procreation. Two of the sexes, thaan and chan, are approximately masculine, and the other two genders, zhen and shen, are approximately feminine. Andorians and Aenar accept the terms "male" and "female", and the pronouns "she/her" and "he/him", while dealing with binary-gendered species. (DS9 novel: Avatar, Book Two)