The first part of the paper explores Aristotle's biological concept of an eidos (species or form) in comparison with modern biological taxonomy. The second part outlines normative determinants of an Aristotelian eidos. The third part considers two passages in which Aristotle compares non-biological eide to biological: pleasures, in EN 10.4-5, and kinds of government in Pol. 4.4.
Preus, Anthony, "Eidos as Norm in Aristotle's Biology" (1977). The Society for Ancient Greek Philosophy Newsletter. 86.