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
Oriental."
"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."