i.e: (po)Larity.  As Gender differentiates male from female, larity differentiates Sime from Gen.

The generic inclusive term for the divisions ‘Sime’ and ‘Gen.’  The human species is divided into two larities, Sime and Gen.   (Source:  NOTES TO COPYEDITOR / To Kiss or To Kill)  No other species in the galaxy is differentiated in such a fashion. 

There are male Gens and male Simes.  There are female Gens and female Simes.  Humanity consists of two genders and two larities.

The term "larity" was invented in a long discussion among Sime~Gen universe fans and fan writers on a Listserve over several years.  Thus the authors Jean Lorrah and Jacqueline Lichtenberg adopted use of the term into the published novels only in the later books.  One may consider it to have been in general usage throughout, and into the space age.

UNIVERSE PREMISE: Life on Earth began as one-celled creatures, and then differentiated into plant and animal, and male and female.  The differentiation into Sime and Gen occurred only to humans, but is of the same magnitude as the differentiation into male and female.