The Aryan migration theory says that a group of people called Aryans came from the steppe region basically the European region to India and brought culture, language etc which we follow and use in the present time. Many nationalists at the time of Ambedkar believed this theory of Aryan migration, but had different opinions on where they came from.Bal Gangadhar Tilak who was the first leader of Indian Independence movement located Aryan homeland in the Arctic circle and Nehru also accepted the trans-Indian origin.Some nationalists argued that the people who were already in India did not have proper culture, language and they were impure at that time, racially different from Aryans. The Aryans arrived in India, imposed the culture, language by conquering them and made them slaves. The Dasas and Dasayus, the names by which they were addressed were called shudras later after conquering. They also separated the white race and the black race. Ambedkar completely denies this theory by making an argument of Aryan not being a race but is the group of people speaking a particular language (Indo-European).
Ambedkar quotes Max Muller demurs, who states “There is no Aryan race in blood; Aryan, in scientific language, is utterly inapplicable to race. It means language and nothing but language; and if we speak of the Aryan race at all, we should know that it means no more than... Aryan speech”.
Also, there was no genetic proof that some people migrated to India and settled here. The people who were supporting the Aryan migration theory, especially the brahmins who believed that they are Aryans and all the non-brahmins are descendants of non-aryan race, this theory helped them to claim themselves of being superior and establish kinship with the Europeans. This led to a huge societal issue, that is the caste system. Ambedkar being the criticizer of casteist society completely disagreed with the Aryan migration theory.
The table has been turned now by the present Hindutva rightwing as the historians,archeologists,geneticists claimed that the language Sanskrit which they believe sacred to Hindu religion doesn’t have an Indian origin.
Tony Joseph, in his book early Indians talks about four groups of people who came to India, one of them being the Aryans. He argues that these four groups of early Africans, Harappans, Aryans and other groups arrived, mixed with each other until they formed their own groups and started marrying internally. This led to the emergence of the caste system.
However, if you look at the origins, no caste is pure as they got mixed earlier. This is the reason why the rightwing oppose the Aryan migration theory in the present because if they believe, the idea of one nation, one religion and following the caste system makes no sense at all and seems stupid. Also the belief of hindus being the indigenous children of the soil and all the culture and language were born here appear meaningless too. This led to a huge controversy between the believers and non-believers of Aryan migration theory. When the Rakhigari DNA report was published after the study of the DNA samples collected from the skeleton found in Rakhigari, many, who were part of the Hindutva threatened the genetic team not to publish it and created chaos by claiming the indegenous origin and making similar statements.
The attempt to make India a Hindu nation enforced by the RSS (rashtriya swayam sevak sangh), the Bharatiya Janata Party (BJP) through making claims of having mosques built after demolishing ancient temples has been relentless. The Ram temple that is being built on the place of Babri masjid that was demolished by the rightwing mob in Ayodhya is a big example.These violences and controversies are constantly affecting the society which, people are unfortunately unaware of.
Sources:
How genetics is settling the Aryan migration debate - The Hindu
Sharma, A. (2005). Dr. B. R. Ambedkar on the Aryan Invasion and the Emergence of the Caste System in India. Journal of the American
Academy of Religion, 73(3), 843–870. Dr. B. R. Ambedkar on the Aryan Invasion and the Emergence of the Caste System in India on JSTOR
Sensitivity Over Aryan Migration Due To 2 Misconceptions, Says 'Early Indians' Author | The Quint - YouTube - Tony Joseph interview by The Quint.
Aryan Invasion Theory: A Myth or Reality? | Dabur Red Paste Arth 2019 - YouTube - Panel discussion consisting of an author,teacher Dr.David Frawley, geneticist Anil Suri,Koenrad Elst and Niraj Rai. (this video was only watched to get my views more clear on Aryan migration. No information has been taken and used in the writing)
Humes, C. A. (2012). Hindutva, Mythistory, and Pseudoarchaeology.
Numen, 59(2/3), 178–201. Hindutva, Mythistory, and Pseudoarchaeology on JSTOR