While the Aryan Invasion Theory/Aryan Migration Theory has been debunked beyond doubt by genetics, its proponents still try to claim ambiguity on other grounds — linguistics, archaeology, mythology etc. — similar to how creationists claim that Creationism is as plausible an explanation as Evolution.
Linguistics evidence
Since genetics debunks AIT/AMT, linguistic arguments are the first refuge for the AIT/AMT apologists. The reasoning is that the similarity between North Indian and European languages means Aryan invasion or migration must have happened. However, the problem with this assertion is that it derives its conclusion from partial information. The similarity of languages could have come from migration on either side — one cannot claim that Europe is the origin for the Indo-Aryan language family based on similarity of Indo-European languages alone. The British, who first propounded AIT/AMT, didn’t like the idea that the west might have had its origin from Indians, so they postulated that Europe gave rise to Indian languages and culture — and this is exactly what people trained in leftist and Marxist schools push even today.
However, recent analysis on linguistics is also making life difficult for AIT/AMT proponents. Recent studies show that Sanskrit has more in common with the proto Indo-European language — which gave rise to the Indo-European language family — than any other European language.
The most important finding from linguistic reconstruction is that Sanskrit has the most in common with the proto Indo-European language, and not the Central Asian or Eastern European languages. For example, Childe gives 72 basic cognate proto Indo-European words constructed scientifically, of which Sanskrit has 70 words, German 46 words, Baltic 23 words, Slavic 16 words, and Greek 48 words. Sanskrit is the only Aryan language besides proto Indo-European to have retained three genders, three numbers and eight cases intact.
Another evidence is presented using ancient mythologies. When you compare Greek and Vedic mythologies, there are many common elements. Similarly, German and Vedic mythologies share many common elements. But if you compare German and Greek, there are no common elements — meaning Sanskrit and Vedic mythology is the common element connecting the European language tree and mythologies. Also, Iranian Mythology has common elements only with Vedic mythology. But according to AIT, Aryans came from South Russia to Central Asia and then separated in Iran. This cannot be the case when Iranian mythology has nothing in common with any other European mythology of that time.
Archaeological evidence
The initial basis for AIT was based on the claim by Mortimer Wheeler when he found some skulls in archaeological sites around Harappa and used them to support AIT by claiming the skulls belonged to Dravidians killed by invading Aryans. However, subsequent archaeological research showed that the skulls were mere burial sites of IVC people and not the result of any fighting between invading armies and locals. In fact, there is no archaeological proof that any kind of invasion ever took place. This is the reason AIT proponents have recently changed their stand to Aryan Migration Theory — much like how creationists changed their theory to “Intelligent Design” keeping all but the name. But unfortunately for the proponents of AMT/AIT, even AMT falls flat on the archaeological evidence: there is no archaeological evidence for any kind of migration into IVC either.
Another popular argument used by the AMT/AIT side is that IVC had no chariots and it was the Aryans who brought chariots and horses into India. This is a preposterous claim. India is protected from the north and north-west by the Hindukush, and any invader had to overcome it. The Greeks, who were known for their chariots, had to leave them behind when Alexander invaded India. So it is nothing more than wishful thinking to assume that nomadic barbarians from Central Asia could have achieved the feat of bringing chariots into India through the Hindukush two thousand years before Alexander — something that even he didn’t achieve. Michael Danino presents detailed evidence showing that horses were present in India much before the supposed Aryan invasion, and some recent studies actually claim horses are native to India.
Ice Age evidence
The world came out of the last ice age roughly around 10,000–12,000 years ago. India was not affected by the ice age to the same extent as Europe and Central Asia because of the presence of the Himalayas to the north. So the population living in India at that time could have easily migrated north towards Central Asia and then Europe as the ice age began to end and glaciers began retreating. This is consistent with what is observed in the genetic studies.
However, AIT/AMT posits the opposite direction for migration. Why would Europeans and Central Asians, who were by then accustomed to ice-covered climate, migrate south into India specially at a time when the ice age had ended and the climate was getting hotter? It makes no sense that people who lived and survived in the ice-covered plains of Europe and Central Asia would abandon their native land specially at a time when it was turning greener and food was getting plentiful. Also, the cold temperature during the Ice Age would have supported smaller populations in Central Asia compared to India. So migration would have been possible only from the high-density area of India to Central Asia and Europe — not the other way around.
Cultural perspective
The latest attempt by AMT/AIT pushers is the theory of cultural assimilation — this way they don’t have to present any genetic or archaeological evidence, merely stating their assertions are true. As per this version, Aryans were not invaders but a small number of migrants — too small to be detected by any genetic or archaeological evidence — who over a very large period of time successfully managed to force millions of people living in IVC to give up their religion and language in favour of Indo-European languages and gods.
This is by far the most absurd explanation for the Aryan Invasion Theory — it assumes that millions of Dravidians living in IVC, which was at that time the most populous region on the planet, had no good language or religion of their own and thus gave up their own civilisation and copied the few hundred migrating Aryans whose numbers were so low that current archaeology or genetic studies can barely detect them. Many people prefer such mental gymnastics rather than the much simpler explanation that the Aryan invasion or migration never happened and that the Aryan-Dravidian divide was an artificial construct of the British.
Even after all these attempts, the Aryan Invasion Theory leaves behind many more questions than it solves. There are crores of temples for Dravidian Gods — Shiva, Vishnu and Brahma — all over India, while the Aryan gods — Indra, Varuna, Vayu, Agni etc. — have very few temples dedicated to them. Unless one is wilfully disingenuous, it makes no sense that the Aryan invaders or migrants who supposedly defeated the Dravidians would have adopted the gods of the Dravidians as the primordial deities above their own Indra or Vayu.
This brings to an end this series of articles. The articles here have tried to debunk the most common arguments used by the supporters of AIT/AMT. Given the amount of propaganda and politics which supports the pro-AIT lobby, the mounting evidence against this theory will take some time to change things on the ground. Till that happens, the job of debunking this theory should continue at all levels.