After the baby was born, the panicked Japanese father went to
see the obstetrician.
"Doctor," he said, "I don't mind telling you, but I'm a little
upset because my daughter has red hair. She can't possibly be
mine."
"Nonsense," the doctor said. "Even though you and your wife both
have black hair, one of your ancestors may have contributed red
hair to the gene pool."
"It isn't possible," the man insisted. "We're pure Asian."
"Well," said the doctor, "let me ask you this. How often do you
have sex?"
The man seemed ashamed. "I've been working very hard for the past
year. We only made love once or twice a month."
"There you have it!" the doctor said confidently. "It's just
rust."
