According to Buddhist cosmology, in the Abhidharmakosha it says that at the beginning of this earth, countless years ago, our lineage grandfather, Vramah and the gods and goddesses were miraculously reborn. They had light and were able to fly. They didn´t eat dirty food, meat, egg or blood. They used concentration food and nectars. (Further information can be found in the Abhidharmakosha and its commentary.)
Many years later, some gods and goddesses ate earth and dirty foods. Their light disappeared and they could not fly. They could not see their companion gods and goddesses. Then they started to have sexual relations. Generations later they ate meat and blood. They started to become violent and kill each other. That was the beginning of being human. Human translates into Tibetan terminology as “mi” or “minang”. “Mi” means "I cannot see my companion gods and goddesses."
Therefore, countless years ago, our lineage grandfather and grandmother gods, did not eat meat. Generations later eating meat became a bad habit. This explanation comes from Abhidharmakosha cosmology.
Abhidharmakosha comes from the seven arhat`s Abhidharma great Buddhist texts. It doesn´t come from Buddha Shakyamuni sutras. Buddhist philosophies agree that our lineage originated from grandfather Brahma and many gods and goddesses. Buddhist philosophy never believed in a creator god. Also, Jain, Sankhya and Carvaka philosophies don´t believe in a creator god.
http://teachingsfromtibet.com/geshe-thubten-soepa/