The term Ayurveda is first mentioned in Sanskrit scripts by Ayurvedic practitioners like Sushruta, Charaka, Kasyap, etc in their Samhitas now known as Sushrutha Samhita, Charaka Samhita, Kasyapa Samhita. Bhela is also another practitioner who mentioned the term Ayurveda.
Ayurveda, in its modern form is believed to have come into existence around 600 BC. The Panchabhoota and Tridosha concepts would have developed from other sciences like numerology, yoga, theology, philosophy, etc.
Ardent lovers, and practitioners of Ayurveda, have written in palm leaves that Ayurveda, as a science of life has no beginning and end. It just passes to the mankind from the cosmic creator of this universe and everything in it Lord Brahma. Lord Shiva and the Sun God too are related with Ayurveda. The knowledge was later transferred to humans through hermits or sages. These sages (called Rishis), mainly Sage Athreya, Dhanwantary, Didodasa, Kasyapa, etc, instructed their disciples. Kasyapa Samhita explicitly tells that Ayurveda, Ayurvedic medicines, and Ayurvedic treatment methods originated well before the advent of human race.
Diseases, according to Ayurveda affect not only humans, but also all living and nonliving things. The sages have named the diseases affecting different living and non living things. Pakalam affects elephant, abhithapam horses, neelika water, ooshara earth, etc. Only humans can recognize the diseases and take appropriate steps to correct the conditions.
These disciples learned all the eight branches of Ayurveda, called Ashtanga or Asthangahridaya, namely Kaya Chikitsa (physician), Bala, Griha (home treatment women and children medicine), Urdhwanga, Salya (Surgery), Visha (toxicology), Rasayana, Vageekarana (aphrodisiac) chikitsakal or treatments.
The disciples later practiced these specializations and became experts in their fields. Sushruta is an example. He specialized in Salya Tantra or the technique of surgery. He is now considered the father of plastic surgery. Susrutha also used anesthesia before surgery.