The Evolution of Bengali

Bengali belongs to the easternmost branch, called Aryan or Indo-Iranian, of the Indo-European family of languages. Its direct ancestor is a form of Prakrit or Middle Indo-Aryan which descended from Sanskrit or Old Indo-Aryan. Sanskrit was the spoken as well as the literary language of Aryandom until circa 500 B.C., after which it remained for nearly two thousand years the dominant literary languages as well as the lingua franca among the cultured and the erudite throughout the subcontinent.
Like Sanskrit, Apabhramsa-Avahattha was a literary language, and in the available records it shows remarkably little local variation; practically the same form of the language appears in the poems written in Gujrat and in Bengal. But the spoken language conditioned by the regional linguistic and ethnic environments took up the different regional New Indo-Aryan languages. The emergence of these New Indo-Aryan speeches was not all synchronized. But some of them, including Bengali, certainly originated by the middle of the tenth century at the latest.
For old Bengali the only records are mystic carya songs discovered in a MS from Nepal by Haraprasad Shastri.The language of the carya songs is basically vernacular, but at the same time it is also something of a literary language.
Bengali at the present day has two literary styles. One is called "Sadhubhasa" (elegant language) and the other "Chaltibhasa" (current language) . The former is the traditional literary style based on Middle Bengali of the sixteenth century. The later is practically a creation of the present century, and is based on the cultivated form of the dialect spoken in Calcutta by the educated people originally coming from districts bordering on the lower reaches of the Hoogly. The difference between the two literary styles is not very sharp. The vocabulary is practically the same. The difference lies mainly in the forms of the pronoun and the verb. The Sadhubhasa has the old and heavier forms while the Chalitbhasa uses the modern and lighter forms. The former shows a partiality for lexical words and for compound words of the Sanskrit type, and the latter prefers colloquial words, phrases and idioms. The Chalitbhasa was first seriously taken up by Pramatha Chaudhuri at the instance of Rabindranath Tagore during the early years of the first World War. Soon after Tagore practically discarded Sadhubhasa, and Chalitbhasa is now generally favored by writers who have no particular fascination for the traditional literary style. The Sadhubhasa is always easy to write but it is somewhat faded in signification and jaded in rhythm.
The Bengali script, like all other Indian scripts, originated from Brahmi alphabet of the Asokan inscriptions.The Bengali alphabet in its present printed form took shape in 1778 when printing types were first cast by Charles Wilkins. There still remained a few archaic forms and these were finally replaced in the middle of the nineteenth century.