Even worse, so far as man's attempt to classify is concerned, is the fact that sometimes filial descendants, that is brother and sister, are intersterile although they are clearly of the same species.
Seega, nagu kõigis küsimustes, et mõista ühe või teise eluala täpsemat sisu, on meil tarvis vaadata, mida Kiri selle kohta ütleb.