As if a two-day discussion on the Indian Parliament's commitment to the constitution was not tense enough, Congress leader Mallikarjun Kharge decided to add even more fuel to the fire. Home Minister Rajnath Singh began the parliamentary discussion with a not-so-subtle reference to film actor Aamir Khan's recent comments about not leaving India despite feeling unsettled.

"Even as he faced insults, Dr Babasaheb Ambedkar never thought about leaving India. He kept on presenting an objective point of view for a unified India," Singh said, in his introductory remarks to the debate on the constitution. Singh also brought up the addition of the words "socialist" and "secular" to the preamble of the Indian constitution, a much-derided act of former Prime Minister Indira Gandhi, although the Congress party continues to defend this. The home minister claimed that Ambedkar, the architect of the constitution, didn't feel the need to add those two words.

This prompted a reply from Kharge on the comments. "I want to tell you that Dr Babasaheb Ambedkar wanted to put the words socialist and secular into the constitution, but he couldn't because of the atmosphere at the time," Kharge said. "Because of this, please stay away from controversial comments.

"Ambedkar wanted to run away? Wo toh mool bharatiya the. (He was an original Indian). You have come from abroad. All these Aryans have come from outside. We are the original inhabitants, the original Indians. We have defended India for 5,000 years."

In doing so Kharge was resurrecting what is known as the Aryan Invasion Theory, also known as the Indo-Aryan Migration Theory, which has been a bugbear of Indian history for decades now. First proposed by Western scholars, the theory suggests that the original Dravidian inhabitants of the subcontinent were invaded by horse-riding Aryans from the Iranian plateau, and eventually came to dominate the region.

The theory has been much criticised by Indian scholars for being orientalist and identifying differences, such as a theory of an Aryan "race," where there is none. It is also frequently vilified by Hindu nationalists uncomfortable with the idea that they might not be the original inhabitants of the subcontinent. In particular it plays into a caste discomfort suggesting that Aryan invaders, who became the Indian upper castes, which is why Kharge brought up the issue, with reference to Ambedkar, the architect of the constitution, who also spent his life attacking the caste system.

Ambedkar himself, however, considered the Aryan invasion theory "leaky" and unfounded. He said there was no proof to suggest that the Aryans were in any way a race, rather than just a people, and that they were somehow superior or inherently different to the Dravidian inhabitants of India. He saw the theory, instead, as a Western attempt to rationalise various data points.

"The Western theory, it is clear, is only a hurried conclusion drawn from insufficient examination of facts and believed to be correct because it tallied with certain pre-conceived notions about the mentality of the ancient Aryans which they were supposed to have possessed on no other grounds except that their alleged modern descendants, namely, the Indo Germanic races are known to possess. It is built on certain selected facts which are assumed to be the only facts. It is extraordinary that a theory with such a slender and insecure foundation in fact should have been propounded by Western scholars for serious scholars and should have held the field for such a long time. In the face of the discovery of new facts set out in this Chapter the theory can no longer stand and must be thrown on the scrap heap," he wrote.