Theravada Buddhism is one of 18 branches of the Nikaya school of Buddhism (and the only surviving branch) that originated in the century following Buddha's death. "Theravada" (is translated as the "Way of the Elders" or the "teaching of the Elders") is the most conservative school of Buddhism that claims to have conserved the teachings of Buddha in their original form. It traces its origins to the Second Council of Buddhism held about a century after the death of Buddha in which the Theras (Elders) condemned the novel interpretations of the Buddhist doctrine and emphasized an orthodox and conservative view of Buddhism. ("Theravada Buddhism" para on Origins) This split between the conservatives and the reformers was further confirmed in the Third Council called during the time of King Ashoka in about 250 BC. The proceedings of the Third Council, refuted the allegedly heretical, and false views held by some Buddhist sects and adopted "Pali Canon"believed to be the earliest record of oral teachings of Buddhaas the only scripture of Theravada Buddhism. (Akira 256-258)
The seeds of evolution of Mahayana Buddhism were sown when the Mahasanghikas, a liberal branch of the Buddhist community, broke away from the more conservative mainstream some time before the reign of Indian king Ashoka in the 3rd century BC. ("Mahayana