How old is your father? Sounds like he made a very good connection with his adoptive parents and thinks of them as his only parents. Some times when you try to find out past things they don't turn out the way you expect and some parts may be hurtful for others, I'm sure if your fathers birth parents could have raised him they would have done so. It's not about the birth mother, she only gave him life. It's about the mother and father who clothed, provided food, shelter, and set beside him when he was sick, and loved him with all their hearts, I know because I was adopted too!!!