Nakshatras have been classified in terms of certain animal species. It is a well known fact that the human embryo in the course of its development in the womb, passes through all the stages of evolution. From a one cellular organism to fish, amphibian, reptile, mammal, quadruped and finally to a human foetus. It is only natural to assume, that there will exist some variety among humans in terms of the degree in which certain stages of evolution have had an influence in their overall structure.
Thus we can understand how the 27 nakshatras, representing all the laws of nature, responsible for the structure and evolution of every soul in creation, can be classified in terms of animal species. In Sanskrit, this classification goes by the name of yoni, referring to the idea of origin, source, place of birth, home, nest, stable, stock, family, race.
Chandra, placed in a certain nakshatra at birth (janma nakshatra) indicates to what origin, or species, family or race the person ibelongsi, which can be easily verified in daily life. The nature and tendencies of the animal reflects itself, to a certain degree, in the nature and tendencies of the person.
Thus, this classification concerns itself with certain psychological (temperamental) and physiological traits of a person. Each of the 14 animals used in this division, has two nakshatras as their domain, one of which is male, and the other female.
This classification also, finds a concrete application in matching two birth charts for marriage compatibility. Ideally marriage partners belong to the same species, but many other combinations are also possible. (For more details see Kalaprakashika, p. 73, and Muhurtha, p. 70)
For ready reference, please find here below the list of 14 species, each with their male and female nakshatras
CLASS OF YONI