Four modes of birth

The four modes of birth (Tib. སྐྱེ་གནས་བཞི་, kyené shyi, Wyl. skye gnas bzhi) — according to tantric theory, all forms of birth fall into one of four categories:

1. womb birth (for humans and certain classes of animals and pretas);
2. egg birth (for certain animals);
3. spontaneous generation from warmth and moisture or heat-moisture birth (for certain “inferior” types of animals), and
4. miraculous birth or manifestation (for all gods, hell beings, and beings in the intermediate state, as well as certain classes of preta and humans such as bodhisattva emanations).