Ayurveda in India
Ayurveda in India—the science of life, the origin of most forms of natural and alternative medicine—has its mention in one of the oldest (about 6,000 years) philosophical texts of the world, the Rig Veda. The Sutrasthana of Charaka Samhita, a much referred ayurvedic text, says; "The three—body, mind and soul—are like a tripod, the world stand by their combination; in them everything abides. It is the subject matter of ayurveda for which the teachings of ayurveda have been revealed." (1.46-47)
In its broader scope, ayurveda in India has always sought to prepare mankind for the realization of the full potential of its self through a psychosomatic integration. A comprehensive health care is what this natural and alternative medicine prescribes for the ultimate self-realization.

"Life (ayu) is the combination (samyoga) of body, senses, mind and reincarnating soul. Ayurveda is the most sacred science of life, beneficial to humans both in this world and the world beyond."
—Charaka Samhita, Sutrasthana, 1.42-43.
The verses of Rig Veda, the earliest source of ayurveda, refer to panchamahabhut (five basic elements of the entire creation), and the three doshas or primary forces of prana or vata (air), agni or pitta (fire) and soma or kapha (water and earth) as comprising the basic principles of ayurveda. One branch of Indian philosophy—Sankhya states that there are 24 elements, all of which constitute the foundation of the gross world: earth, water, fire, air and ether. These five elements in different combinations constitute the three body types/doshas—vata dosha (air and ether), pitta dosha (fire) and kapha dosha (earth and water). The panchamahabhut and the dosha theories are the guiding factors of ayurveda as a therapeutic science. The Rig Veda also mentions organ transplants and herbal remedies called soma with properties of elixir.
This science or knowledge of healing, as mentioned in the Rig Veda, was revealed to Rishi Bharadvaja from the great Cosmic Intelligence. The knowledge consists of three aspects known as the Tri-Sutras of ayurveda, which are—etiology or the science of the causes of disease, symptomatology or the study and interpretation of symptoms and medication and herbal remedies.
Approximately, during 4,000 to 3,000 BC, Sam Veda and Yajur Veda, the second and third Vedas came into being. Chanting of mantras and performance of rituals were, respectively, dealt in these two Vedas. And, during 3,000 to 2,000 BC Atharva the fourth Veda was authored, of which ayurveda is an upaveda (subsection). Though it had been practiced all along, it was around this time that ayurveda in India, was codified from the oral tradition to book form, as an independent science. It enlists eight branches/divisions of ayurveda: Kayachikitsa (Internal Medicine), Shalakya Tantra (surgery and treatment of head and neck, Ophthalmology and Otolaryngology), Shalya Tantra (Surgery), Agada Tantra (Toxicology), Bhuta Vidya (Psychiatry), Kaumarabhritya (Pediatrics), Rasayana (science of rejuvenation or anti-aging), and Vajikarana (the science of fertility). The oldest treatise available on this codified version is Atreya Samhita.

The most fascinating aspect of ayurveda is, it was using almost all methods of healing like lifestyle regimen, yoga, aroma, meditation, gems, amulets, herbs, diet, jyotishi (astrology), color and surgery etc. in treating patients. Though ayurveda came into being as an independent upaveda of Atharva Veda, it has close links with other Vedas also. The Yajur Veda, which recommends rituals to pacify the panchamahabhuts in a view to heal both the Cosmic Being and the individual soul, is related to ayurveda in its principles and regulations of lifestyle. The upaveda called Dhanur Veda or the martial arts and ayurveda both refer to each other in the treatment of marmas or sensitive points in the body. Ayurveda recommends specific ayurvedic massages, exercises and bodywork for this purpose.
Around 15,00 BC ayurveda was delineated into to two distinct schools: Atreya—The School of Physicians, and Dhanvantari—The School of Surgeons. This made ayurveda a more systematically classified medical science, hereafter. Dhanvantari, who is considered to be a reincarnation of Lord Vishnu, was the guiding sage of ayurveda. He made this science of health and longevity popular and widely acceptable. In fact, these two schools of thought led to the writing of two major books on ayurveda—Charaka Samhita and Susruta Samhita.
These two Samhitas were written in the early part of 1000 BC. The great sage- physician Charaka authored Charaka Samhita revising and supplementing the text written by Atreya, which has remained the most referred ayurvedic text on internal medicine till date. Susruta, following the Dhanvantari School of Thought, wrote Susruta Samhita, comprising the knowledge about prosthetic surgery to replace limbs, cosmetic surgery, caesarian operations and even brain surgery. He is famed for his innovation of cosmetic surgery on nose or rhinoplasty. Around 500 AD, Vagbhatt compiled the third major treatise on ayurveda, Astanga Hridaya. It contained knowledge comprising the two schools of ayurveda.
From 500 AD to 1900 AD, sixteen major Nighantus or supplementary texts on ayurveda like Dhanvantari Bhavaprakasha, Raja and Shaligram among others were written incorporating new drugs, expansion in applications, discarding of old drugs and identification of substitutes. These texts mention about 1814 varieties of plants in vogue.
Evidences show that ayurveda had nurtured almost all the medical systems of the world. The Egyptians learnt about ayurveda long before the invasion of Alexander in the 4th century BC through their sea-trade with India. Greeks and Romans come to know about it after the famous invasion. The Unani form of medical tradition came out of this interaction. In the early part of the first millennium ayurveda spread to the East through Buddhism and greatly influenced the Tibetan and Chinese system of medicine and herbology. Around 323 BC, Nagarjuna, the great monastic of Mahayana Buddhism and an authority on ayurveda had written a review on Susruta Samhita. In 800 AD ayurveda was translated into Arabic. The two Islamic physicians Avicenna and Razi Serapion, who helped form the European tradition of medicine, strictly followed ayurveda. Even, Paracelsus, considered to be the father of the modern western medicine toed the line of ayurveda, as well.
In the postmodern age, the popularity of this vibrant tradition of ayurveda lies in its, subtle yet scientific, approach to heal a person in its totality. It aims, not only at healing the body, but also the mind and spirit, at one go. Its unique understanding of the similarities of natural law and the working of human body, as well as its holistic treatment methods, help it to strike a balance between the two. This gives ayurveda an edge over other healing systems. Perhaps that's the reason behind ayurveda being the longest unbroken medical tradition in the world, today.