going through this thread some replies were quite bemusing. talking about dravidians were arabs before being dravidian and other interesting things. ive explained this in another thread at greater length, search the one on 'scythians'.
but @
pk_baloch, for your convenience i'll just summarize.
the first anatomically modern human beings (homo sapiens) were in east africa approximately 100,000-110,000 years ago.
in the first wave of migration around 80,000 years before present (ybp), some of these humans travelled north through sudan, egypt and populated the middle east region, settling over time near major rivers (nile, tigris, etc).
second wave of migration occurred around 60,000 y.b.p. from east africa, by some early predecessor of the log boat across arabian sea to southern tip of the subcontinent.
most of those stayed back in the subcontinent, referred to as the proto-dravidians. however, some of them continued to travel by water again (around 40,000-50,000 y.b.p) through the extremely shallow, almost land bridge-like route across oceanic islands and ended up in australia to become the aboriginals.
proto dravidians soon began to diverge in terms of population, those who settled in the north around indo-gangetic plains developed slightly different features and skin tone because they were further from the equator near himalayas. over thousands of years their genetic variation was grouped as 'Ancestral North Indians', whilst those that remained in south were 'Ancestral South Indians' in anthropology and genetics parlance.
so yes, we all had common ancestors from east africa. the first people to settle around the indus were descendants of these proto-dravidians, but it's not established whether they were Ancestral north indians or Ancestral south indians, though most likely a mix of both according to circumstantial and inferrable genetic evidence.
discoveries have shown that the indic inhabitants of indus valley/ghaggar hakra traded with their 'cousins' in mesopotamia about 4,500 y.b.p. The demise of it was likely due to floods or environmental disaster forcing most of the surviving inhabitants to migrate eastward, where another civilization emerged near yamuna, ganges.
there's a number of western studies on the origins of south asians. they show the genetic make-up of the subcontinent to be consistent for past 35,000-40,000 years and no external influence worth mentioning to the gene pool, with iranic people arriving and settling near the banks of indus only over the past 2,000 years or so, and mongolic people in north east migrating here even after that.
the point is, learn history from a scientific point of view (archaeology and genetic markers) if you're that interested in our collective origins. it's a humbling experience and leaves no room for complexes of any sort.