The prevailing wisdom used to be that baldness came from the mother’s side of the family. But medical experts now agree that both sides of the family can influence the tendency toward baldness.
Since baldness is a pretty common problem, it’s hard to find families with members who aren’t bald and it’s hard to trace the source.
It all comes down to the luck of the genetic draw, and you can no longer simply blame Mom’s dad for your hair loss.