tabula rasa

Several years ago I learned about the concept of tabula rasa, which asserts that a baby is born with a mind that is largely a blank slate.  Personality, behavioral tendencies, intellectual capacity, etc are all things that spring out of the environment a child is raised in rather than from genetics.

I have heard from various sources that research done in the last two or three decades has largely discredited the idea of tabula rasa to the point where it is not a seriously held position in academic circles now, though not long ago this was not the case.  Having had two kids I have to strongly question how anyone who raised more than one child ever believed in tabula rasa.

While our kids are still young--just seven and nine--it is striking and unavoidable to see where specific aspects of our kids' drives and personalities are not only unique, but have been that way from birth.  In fact, I have a very difficult time believing that someone could have kids and not notice this, as I see this uniqueness in a lot of the other kids I am occasionally around as well.  Kids with strong personalities always had strong personalities, and they often have siblings with completely different personalities, though they grew up in the same household.  Things like birth order play a part, but only as an outgrowth of what they were from the start.

If it is obvious to a parent that the foundations of our kids' personality is due to nature rather than nurture--and I have definitely heard other parents observe this as well--why was this not obvious to the academic world for a large percentage of the twentieth century?  Do (or did, since this idea is no longer widely held) academics in psychology/psychiatry simply not spend time with and observe their own families?  It's baffling!