In search of Bengali root

Years back I had an interesting encouter in a so called jungle resort in Masinagudi (Tamilnadu), where we stayed for a couple of days. We had a young man as our guide. He could speak Tamil fluently which we did not understand and had a limited vocabulary with English which was our only common language of communication. He told us that he was born in Srilanka and was brought up in a local Christian church and though he never went to school, he learnt many things from the learned people who happened to visit the place. When he asked us where we are coming from, one of my young Bengalee friends explained to him that he comes from Calcutta which is the capital of West Bengal, a state in the eastern part of India. To that our guide affirmed him that he knew about Bengal. He also told us with absolute certainty [he had a tone that fathers use when they teach their kids not to question the authority of a father's knowledge] that  all Bengalees are originally Tamil and the Tamils migrated many centuries back to Bengal and became Bengalees. Being outstripped of his originality in such a cavalier manner, our Bengalee friend was naturally enraged. Others cajoled him not to take it too seriously since the guide is telling him what the guide has heard and that the guide was not particularly an expert in the field.
If you thought that it was only the Bengalees who react in that manner, few days back I met a Malayali gentleman who was so taken into believing that Syrian catholic Malayalis are not from India, that he was willing to fund a blood sampling study to establish the truth beyond anyone's doubt.
Fact is our regional or clanish identity is at the very root of our self-identity but however one likes to believe that they are direct descendent of Moses or Lord Rama, ours is a common history of migration.

Early Human Inhabitation to Early Human Civilization in India
It is now established scientifically that human species i.e. Homo Sapiens came to being in African continent and has moved to different areas of the planet from there. Migration is a natural process of the growth and expansion of population. Continental migration of human species particularly Homo sapiens started almost 60,000 years ago [Homo Erectus moved many thousands of years before that] and as established by Mitochondrial DNA research, the migration route covered Indian subcontinent squarely. The research also establishes that migration happened multiple times with natural disaster taking the role of the mighty Devil that periodically wiped out species from many parts of the planet [see National Geographic Atlas of the Human Journey for more details].

 Cave painting at Paachmari

Undoubtedly the group of australoids who migrated 60,000 years ago were a bunch of hunters/gatherers, still a long way to evolve into a collective who can build intelligent self-contained colony. In fact there are cave paintings, in Paachmari and Bhimbekta caves in Madhyapradesh, India that ASI has dated to be at least from 12,000- 10,000 BCE. The drawings demonstrate that  minds of these early human population in India were mostly preoccupied with animals that they hunt. It probably took at least another 5000 years before they adopted agriculture for their livelihood.

MehrGarrh earthen pot 7000 BCE

That brings us to the question of earliest civilization in Indian subcontinent. The latest evidence shows that India had established agrarian civilization as early as 7000 year BCE. The Mehrgarh excavation brought first time to our knowledge that India had civilizations well before Harappa era. They establsihed knowledge of  building mud-houses and farming wheat and barley. A stone axe and mud-brick house complex were found that date to early Mehrgarh period. Discovery as late as in 2006 established that they were the first in the world to demonstrate proto-dentistry capability. "Here we describe eleven drilled molar crowns from nine adults discovered in a Neolithic graveyard in Pakistan that dates from 7,500 to 9,000 years ago. These findings provide evidence for a long tradition of a type of proto-dentistry in an early farming culture" [source: wiki/nature]
There is however no evidence of any written language which means that tracing our present language-based identity to Mehrgarh era is moot.
Early Languages in India and Bengali
Linguists claim that earliest spoken language in India was proto-dravidian. Linguistic reconstruction suggests that Proto-Dravidian was spoken around the third millennium BC, possibly in the region around the lower Godavari river basin in peninsular India. The material evidence suggests that the speakers of Proto-Dravidian were the culture associated with the Neolithic complexes of South India The next phase in the reconstructed proto-history of Tamil is Proto-South Dravidian. The linguistic evidence suggests that Proto-South Dravidian was spoken around the middle of the second millennium BC, and that proto-Tamil emerged around the 3rd century BC.[source: wiki]
Compared to that, Sanskrit appears only with the Indo-Aryans i.e. at around 1500 BCE. Now as far as Bengali is concerned, the language did not exist before Christ era. Historical evidence tells us that Bengali evolved from Prakrit at around 9th-10th century AD, although Prakrit was not a single language. Prakrit more likely refers to all the dialects spoken in North India when Sanskrit became the language of elites, particularly the academics. Prakrit and Pali are considered to be direct descendent of Sanskrit. They came almost at the same time and were spoken during Buddha's time i.e. as early as 600-700 BCE. In other words, Tamil although is far more ancient language compared to Bengali, Bengali as the language does not appear to share the root with Tamil. Bengali is decidedly an Indo-Aryan language while Tamil is rooted to its dravidian origin.
Language is not the only artefact
 However it will be a mistake to look at the identity issue only through the lens of language. Culture is much larger aspect of identity and language is just one constituent of the culture, a mere communication tool for the population sharing the culture. Migration is more ancient aspect of human civilization and migrant community is known to adopt the culture of teritory that they migrate to. Therefore a better approach would be to trace the migration history to Bengal.
Early Settlers in Bengal to Bengali Empire
"Historians believe that Bengal, the area comprising present-day Bangladesh and the Indian state of West Bengal, was settled in about 1000 B.C. by Dravidian-speaking people who were later known as the Bang. Their homeland bore various titles that reflected earlier tribal names, such as Vanga, Banga, Bangala, Bangal, and Bengal." [source: Bangladesh: A country study. Library of Congress. ]
Some argue that the name Bengal is derived from Vanga (Bôngo), which came from the Austric word "Bonga" meaning the Sun-god.
"Stone age tools dating back 20,000 years have been excavated in the state. Remnants of Copper Age settlements in the Bengal region date back 4,000 years. Stone tools provide the earliest evidence of human settlements. Prehistoric stone implements have been discovered in various parts of West Bengal in the districts of Midnapur, Bankura and Burdwan, and also at Sagardighi. But it is difficult to determine, even approximately, the time when people using them first settled in Bengal. The original settlers spoke non-Aryan languages— they may have spoken Austric or Austro-Asiatic languages like the languages of the present-day Kola, Bhil, Santal, Shabara, and Pulinda peoples. At a subsequent age, peoples speaking languages from two other language families— Dravidian and Tibeto-Burman—seem to have settled in Bengal." [wiki]
But there is also mention of Vanga empire in Mahabharata. Vanga was neighbour to Anga which was ruled by Karna.  Bhagadatta was mentioned as the King of Vanga who joined the Kauravas in the battle of Kurukhestra.
 According to Mahavamsa, the ancient Buddhist literature, the Vanga prince Vijaya Simha conquered Lanka (modern day Sri Lanka) in 544 BC and gave the name "Sinhala" to the country. Bengali people migrated to the Malay Archipelago and Siam (in modern Thailand), establishing their own colonies there. ^[source]  Notwithstanding the fact that historians suffer hugely from lack of objective evidence here, one curious piece of information is that present Sinhala [source] is considered an Indo-aryan language like Bengali although regional proximity demands that it should belong to Dravidian language class. Closest relative of Sinhala is the language of the Maldives and Minicoy Island (India), Dhivehi, places that are claimed to be colonized by Bengalees. This kind of supports that claim made in Mahavamsa.
  Coming back to early migration, This page claims that the civilization that flourished in this region before the Aryans came, was the Alpine civilization. The Alpines (Eastern Bracycephalic) from Taklamakan Desert in Central Asia settled in eastern India (Bengal, Orissa and the plains of Assam) and formed the main elements of today's Bengali people. The Alpines were divided into various indigenous tribes: Vanga (south Bengal), Pundra (north Bengal), and Rarh/Suhma (West Bengal) according to their respective Totems.
Greek accounts mention of Gangaridai [spelt differently in different places but is consdered largely the area known as Bengal] empire that existed in the Ganges valley when Alexandar invaded Indus valley. "Among the southern countries the first under the Kaukasos is India, a kingdom remarkable for its vast extent and the largeness of its population, for it is inhabited by very many nations, among which the greatest of all is that of the Gandaridae, against whom Alexander did not undertake an expedition, being deterred by the multitude of their elephants. This region is separated from farther India by the greatest river in those parts (for it has a breadth of thirty stadia), but it adjoins the rest of India which Alexander had conquered, and which was well watered by rivers and highly renowned for its prosperous and happy condition." –Diodorus Siculus (1st century AD). Quoted from Ancient India as Described in Classical Literature, John W. McCrindle, p. 201.
According to Dr. N.K. Sahu's opinion, the illustrious Ganga Dynasty of Orissa (and also Karnataka) were the descendants of the Gangaridai people who migrated to South India from Tamluk (Midnapur) in South Bengal. He further implies that the Gangaridai people inhabited the entire eastern coast of India stretching from Bengal to Kalinga.
"The Nandas who ruled in the 4th century BCE originated from Bengal and they defeated the Shishunaga dynasty around 450 BCE and joined the crowns of Gangaridai (Bengal) and Prasii (Magadha).  Dhana Nanda was the king of this empire during the invasion of Alexander the Great." –Bangladesher Itihash.
Middle Ages till British Rule
 During pre-middle ages [750–1174 AD], the Pala dyansty ruled a large part of Indian subcontinent. Their patronage on Buddhism saw establishment of the largest Buddhist Vihara [Sompura] of India and rise of Tibetan Buddhism [which owes its existence to another Bengali named Atish Dipankar].  While Pala dynasty appeared to have risen from Bengal, the next powerful dynasty in Bengal i.e. Sena dynasty, historians believe to have come to Bengal from Karnataka region. Sena dynasty is attributed to bring back Hinduism and strong caste-system to Bengal.
Muslim dynasties took over shortly after Sena period and ruled Bengal off and on till British won the battle of Plassey in 1757 and established Calcutta as the capital for India for next hundred years.

To conclude, it appears that for a very long time, Bengal has been a prosperous melting-pot of different ethnicities irrespective of language and religion. Although the present Bengalees owe their ethnicities to Dravidian, Aryan, Mongoloid and Australoid predecessors, perhaps that mixing of ethinicities have given them the intellectual diversity and other uniquely Bengalee traits which they are so known for. It also appears that ancient migrants in Bengal adopted Sanskrit as the language pretty early and merged into Indo-Aryan population perhaps many centuries before Buddha was born [5th century BCE]. Because their language at that time was already distinctly Indo-Aryan although not quite Bengali as Bengalees speak today, when they migrated to Srilanka and the far east islands, their language remained Indo-Aryan even after natural evolution of languages, which in a way explains why Sinhala is a distinctly Indo-Aryan.
It appears therefore that the guide's conviction was not entirely misplaced.