Sifir species generally reproduce sexually and only with their own particular species but they are all able to have offspring with one another, producing a child that is either one race or the other. The Sifir descendant species cannot have mixed offspring with one another. In the Kykr civilisation, three sifir species live intermingled with one another in mixed relationships.
Sifir races are commonly of average intelligence albeit at different levels of development and technology. Particularly the dru'un and hessak, are both on the lower scale of development. The kuna are among the smartest and most devious sifir species.