After their baby was born, the panicked father went to see the obstetrician.

"Doctor," the man said, "I don't mind telling you, but I'm a little upset because my newborn daughter has red hair. She cannot possibly be mine!!”

"Nonsense," said the doctor. "Even though you and your wife both have black hair, one of your ancestors may have contributed the red hair to the gene pool."

"It isn't possible," the man insisted. "This can't be, our families on both sides had jet-black hair for generations."

"Well," said the doctor, "let me ask you this. How often do you have sex?"

The man seemed a bit ashamed and replied, "I've been working very hard for the past year. We've only made love once or twice every few months."