Born again: How a belief in reincarnation redefined some people's relationships with nature and with each other

Reincarnation is the belief that makes Hinduism different from most other religions. Each living thing possesses an individual spirit ( atman) which is part of an über-spirit ( brahman), the universal force that binds together all life. The goal of all individuals is to liberate the atman, freeing it to join the brahman in eternal bliss. Its destiny is to be recycled again and again in any living thing, plant, animal or human, until it reaches a sufficiently advanced state of development to attain enlightenment ( moksha) and eternal liberation.

Individual spirits can be freed through the practice of meditation. In the "Gita", Krishna goes into exquisite detail explaining to Arjuna precisely how an individual can free his or her spirit by stilling the mind of selfish desires, using as many as four different types of yoga.

The doctrine of reincarnation helped ancient Indian civilisation come to terms with the waves of migration, invasion and violence that have sporadically plagued the south Asian subcontinent. A divisive social structure, known as the caste system, evolved as a response to the increasing complexity of Indian society as different cultures and traditions all piled on top of each other into one space. Rather than each new culture blending in to create diverse social groups, the Indian way of life evolved as a kind of multi-layered cake of people who preferred not to mix.

The idea probably originated from the first bronze-wielding invaders who charged in on horse-and-chariot from the north and west from about 1500BCE, bringing with them their priests, writing (Sanskrit) and a belief in many different gods, such as Indra, the god of war and thunder.

Originally there were only four castes. Brahmans were priests who prayed; kshatriyas were the soldiers who fought; vaisyas the farmers and artisans who worked; and finally sudras, at the lowest end of the scale, dealt with everything that was "unclean".

Mixture between these classes was never encouraged; each one therefore maintained its own identity and culture. However, the idea of reincarnation gave these people some hope that, in the next life at least, there was a prospect of joining the ranks of the higher castes.

Organising a human civilisation into castes has stood the test of thousands of years because it has provided an effective way of dealing with generations of immigration without causing existing cultures to feel threatened by the dilution or extinction of their own distinctive ways of life. Each time a major new culture arrives, a new caste comes into being, finding its place above or below those already there, without any need for radical adjustments of existing customs or habits. As a result, this system has ensured that ancient cultures and beliefs have been preserved longer in India than in most other parts of the world, which helps explain why Hinduism is the longest-surviving religion in all human history.

Veneration of nature, rather than violence towards it, is a distinctive characteristic of Hindu thought. The Upanishads are a collection of ancient Hindu texts, first written down in about 500BCE, designed as commentaries to help interpret the Vedas. In them, the term ahimsa is introduced, a vow that many Hindus take to be non-violent towards nature. Vegetarianism is part of this philosophy, and for this reason as many as 40 per cent of all Indians are vegetarian to this day – that's about 300 million people. Even those Hindus who do eat meat hardly ever eat beef, since the cow is venerated above all other animals as a gift from nature providing milk to drink, power for pulling ploughs and manure for nourishing the soil. For Hindus, the sacred cow is a symbol of unselfish natural giving and cow-slaughter is still banned in almost all Indian states today.

This respectful, peace-loving relationship with the natural world was deeply influenced by four men who, between them, shaped how humans realised it was possible to adapt their civilisations to live in harmony with natural world. Two of them founded religions, the other two helped spread them around the world.

will power: two princes who renounced worldly goods and sought spiritual enlightenment

Siddhartha Gautama, the first of these important figures in the history of Indian religions, was an prince called who is thought to have lived in India from about 563BCE to 483BCE. The only historical evidence of his life comes from texts written by his followers some 400 years after his death, so some of the details may well have merged into myth over centuries of oral rendition.

He was born in Lumbini, in modern-day Nepal. His mother, Queen Maya, died a few days after his birth, leaving him to be brought up by his father, Suddhodana, a king or tribal chief, who had three palaces built in honour of his newborn son. His father wanted to shield Siddhartha from religious teaching and knowledge of human suffering, thinking that this would allow him to become a strong king.

But, at the age of 29, Siddhartha left his palaces to meet his subjects. His father tried in vain to remove all signs of poverty and suffering, but to no avail. On his first outing Siddhartha saw an old man – until then he knew nothing of the trials of old age. On further visits he met diseased and dying people. Greatly disturbed by what he had seen, Siddhartha fled from the luxuries of his palaces to live as a monk, begging for food in the streets. He then became a hermit and, with the help of two teachers, learnt how to meditate and to still his mind.

Next, Siddhartha and five companions tried to find enlightenment by the total denial of all worldly goods, including food – at one time they ate no more than a single leaf or nut a day. After collapsing in a river and nearly drowning, Siddhartha discovered what came to be known as the "Middle Way" – a path towards enlightenment (liberation of the atman) that could be accomplished without the need for extremes, whether of self-indulgence or self-denial.

After receiving the gift of some rice pudding from a village girl, Siddhartha sat under a tree until he found the Truth. After 49 days of meditation, aged 35, he at last attained enlightenment, and from then on became known as the Buddha, meaning "awakened one".

For the next 45 years the Buddha journeyed by foot around the plain of the Ganges River, in north-east India and southern Nepal, teaching his doctrine to a wide range of people, from royalty to terrorists and beggars. After making thousands of converts, he died at about the age of 80, perhaps of food poisoning.

Buddha's teachings were really an extension, or popular interpretation, of many traditional Hindu beliefs. They were of enormous appeal, especially to the poor, for whom there was little hope of social or material improvement. The Buddha explained how by following his "Four Noble Truths" and the "Noble Eightfold Path", these people could rid themselves of inner desires and free their spirits to eternal liberation without the involvement of any priest, king or other intermediary.

Another prince who lived at about the same time as Gautama also renounced his kingdom, and is said to have attained spiritual enlightenment after wandering for 12-and-a-half years in deep silence and meditation. This man was known as Mahavira, meaning "great hero", and he became the 24th and last prophet ( tirthankar) of the Jain religion.

Jain scriptures were written over a long period of time, but the most popular work was written by an Indian monk called Umaswati more than 1,800 years ago. In his Tattvartha Sutra, or Book of Reality, the main aspects of Jainism are set out, identifying its central belief that all life, both human and non-human, is sacred.

For Jains, there is no justification for killing another person, however greatly provoked or threatened. They refuse all food obtained by unnecessary cruelty. Jains are vegetarians and avid supporters of animal welfare. In many Indian towns today animal shelters are run by Jain people. Root vegetables are avoided, as harvesting them destroys an entire plant, whereas fruit, such as an apple, is acceptable, as picking it will leave the tree unharmed.

Non-violence, religious toleration and respect for nature are cornerstones of the Jain philosophy, which, like Hinduism and Buddhism, is concerned with liberating the individual's soul through enlightenment accomplished through a series of codes of conduct that involve taking five vows: of non-violence to all living things ( ahimsa); truthfulness ( satya); non-stealing ( asteya); chastity ( brahmacharya); and detachment from material possessions ( aparigraha).