For example, if I had a kid born with blond hair when both parents have brown hair, I would be suspicious of the mother because neither of us have that trait. Has the concept of inheriting traits from parents been around as long as humans, or is it a (relatively) recent revelation?
addressing the science part of your question (since you're asking *realise that.. * ) . the hair colour example is probably not the best. hair colour can change with age. newborns often start out with little hair. although it remains valid for other traits (eye colour, skin colour, nose shape ), with varying degree of correlation (with parents or grandparents).