Everybody from the Indian sub-continent must have some Harappan ancestry; either those who actually lived in the heyday of the Indus-Saraswati Valley Civilisation (3300 – 1300 BC) or those who dispersed through India as that civilisation declined and intermingled with the existing populations. This intermingling over about 1000 years, of Harappans with those already settled from previously blended populations (pre and post-Toba) is probably one of the key gene dispersal mechanisms on the sub-continent.
Excavations are still adding new details but what is quite clear is that while some Harappans may have moved north-east during its decline, most of them were absorbed into India.
Deciphering Harappan script: The Indus-Saraswati Valley civilisation reached its peak around 1,900 BCE. It had been flourishing there for over a millennium from about 3300 BCE. But various proto-Harappan cultures had existed in those fertile plains for almost 4,000 years before that (from about 7,000BCE). At their peak they occupied the entire Indus -Saraswati Valley and stretched as far as the Indo-Gangetic plain. At its peak there were some 1,000 settlements and at least 5 “great” cities that we now know of; Mohenjo-Daro, Harappa, Ganweriwala, Rakhigarhi and Dholavira. None of these are truly coastal and it is not improbable that one or perhaps two “great” coastal cities are now submerged and waiting to be discovered. Only about 10% of the known sites have been investigated and the Indus Valley script – which I call Harappan for convenience – has yet to deciphered.
… In my narrative it is the Harappans and their language which provided the nucleus for, and eventually became, the family of Dravidian languages. In fact it is probable that some of the roots of what became Hinduism came also with them. I would even suggest that the specialisation of functions (administrators, priests, traders, craftsmen and labour) that must have existed in the meticulously planned, water-resourceful, trading cities of the Indus-Saraswati Valley led to the foundation of guilds and a stratified society. That probably laid the foundations of the caste system which, in its perverted form, currently disgraces the subcontinent.
Andrew Robinson looks at the state of the decipherment of the Harappan script in Nature.
Nature 526, 499–501 (22 October 2015) doi:10.1038/526499a.