What is always in front of you but can't be seen?

A little girl asked her father:
"How did the human race appear?"
The father answered, "God made Adam and Eve;
they had children; and so was all mankind made."
Two days later the girl asked her mother the same question.
The mother answered,
"Many years ago there were monkeys from
which the human race evolved."
The confused girl returned to her father and said,
"Dad, how is it possible that you told me the
human race was created by God,
and Mom said they developed from monkeys?"
The father answered,
"Well, Dear, it is very simple.
I told you about my side of the family,
and your mother told you about hers."