Back in the day, it was commonly assumed that babies are born as "blank slates" -- tabula rasa. Their personalities would develop solely based on how they were raised, with no input from biology. Some people still promote this idea today, but in general it's understood that we are all a product of both nature AND nurture.
|"Tabula Rasa", the blank slate|
My brother, adopted at 10 weeks of age, was certainly viewed as a blank slate, to be molded into his new father's image of a perfect child. It's less clear what my grandparents believed about me, since I was already 16 months old. But I have no doubt that they were certain that their excellent child-rearing skills would overcome all.