Clades are central to "the fiction" (1) of the Strange Stars setting. To paraphrase Wikipedia, clade is a biological term for a group of organisms consisting of an ancestral organism and all its lineal descendants; collectively this group forms a branch on the tree of life. In the Strange Stars setting, we use the term clade to refer to any distinct subspecies of sophont (intelligent being), whether that being is a biologic (traditional organic), moravec (self-reproducing machine), or infosophont (software AI) lifeform.
Still with us?
The concept of clade is central to the fiction of Strange Stars because humanity has spread out among the stars for a long time. Many distinct subspecies of humans exist. Many look like aliens. Some may have alien genes. Some may be entirely alien or machine, but are viewed now as part of an ecumen of intelligent beings.
My Strange Stars games tend to run very pulpy, but there is no reason why you couldn't build a whole campaign exploring how this evolution (or human/alien/AI-induced genome change) occurred. Maybe some of the people, factions, and machines that engineered this cladistic diversity are still out there, waiting to be discovered?
The Strange Stars Fate Edition Rulebook gives players 26 clade templates to start with, and the Threats section of the book contains others that can be put to good use by creative players and GMs. It is also straightforward for players to hybridize two clades, or create new clades of their own. The rulebook will tell you how.
I'll leave you with these words from J.B.S. Haldane, courtesy of Wikipedia:
-What is Life? The Layman's View of Nature (1949)
(1) If there were ever an over-used term in contemporary gamespeak, it is "the fiction". (And why never "the fictions"?) Yet it seems appropriate usage here, because we are talking about deep setting and the implications that flow from it.