There was no time where either the stream of life or the stream of intelligence did not flow' says Charaka. Ayurveda was initially conceived by the Creator-Brahma along with the 4 Vedas - the 'Repository of human wisdom' and is considered as Upaveda of Atharwaveda by virtue of its proximity to Atharwaveda in its contents.
In fact Atharwaveda describes a number of diseases, and 4 types of management strategies viz, Atharvanee, Angeerasee, Daivee and Manushyaja with reference to treatment through holy chants, plant and animal parts, divine/propitiatory rites, and human contrivance by means of drugs, respectively in order to protect life. These strategies are elaborated further in the ayurvedic classics.
By going through the ancient ayurvedic works it is possible to consider 3 schools of Ayurveda which prevailed in ancient times, viz a) Athreya sampradaya (school of medicine) ,b) Dhanwantari or Susruta sampradaya (school of surgery),and c) Kashyapa sampradaya (school of pediatrics and obstetrics).
As mentioned earlier, Lord Brahma the propounder of Ayurveda imparted this science to Prajapati who in turn taught the same to Ashwins, the celestial twin physicians, they in turn taught Ayurveda to Indra. Up to this stage the lineage is common to all the 3 schools of Ayurveda. Thereafter, according to Athreya school sage Bharadwaja learns Ayurveda from Indra and imparts to sage Athreya who in turn teaches his disciples viz Agnivesha, Bhela, Hareeta, Jatukarna, Parashara, Ksharapani and others who wrote their individual treatises on Internal Medicine.
In case of Dhanwantari school, Dhanwatari or Divodasa learnt Ayurveda from Indra and taught the same to his students viz, Sushruta, Aupadhenava, Vaitarana, Aurabhra, Paushkalavata, Karaveerya, Gopurarakshita, Bhoja and others who later wrote their individual treatises on Surgery. In case of Kashyapa school, sage Kashyapa, Vasista, Atri, Bhrugu, their sons and disciples learnt Ayurveda from Indra and wrote their treaties on Kaumarabhrithya/(Pediatrics & Obstetrics).
Ayurveda is also called Astagaayurveda, with 8 divisions, viz, 1) Kaya (study and management of disorders related to digestion and metabolism), 2) Kaumarabhrithya (Pediatrics & Obstetrics) 3) Bhootavidya (study and management of disorders arising from super human influences like constellatory changes, evil spirits, etc) 4) Shalakya or Oordhwanga (study and management of ENT and Eye diseases), 5) Shalya chikitsa (Surgery), 6) Damstra (Toxicology including study and management of sting/bites, etc) 7) Rasayanatantra (Rejuvenation therapy/ Geriatrics& Gerontology) and 8) Vajeekaranatantra (study and management of disorders relating to reproduction and tt related to promotion of virility).
These 8 divisions are broad based but are interrelated. Therefore in order to understand Ayurveda well and be a good ayurvedist either as a teacher or practitioner it is necessary to study all the 8 divisions.
Although Ayurveda is understood as the science related to humanlife it will be interesting to know that there were different types of Ayurveda in the past. Hasty Ayurveda or Palakapyatantra dealing with elephants and their care, horses, cattles, etc referring to veterinary science has been mentioned by Hemadri the 14th century commentator on Astangahridaya.
He has also used the term Rasayurveda in another context. Sharngadharapadhati or Vrikshayurveda (medico botany) of Shangadhara of 14 AD mentions 'nana vrkshayurveda shastrebhyah', indicating there were many works in Sanskrit bearing on Vrikshayurveda . This enables one to conclude that Ayurveda was of different types like Hastyayurveda, Vrikshyaveda, etc in order to preserve the fauna and flora essential for protecting biodiversity and keeping the eco system in absolute balance, to the advantage of human society.