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 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. '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. 'I've been working very hard
for the past year. We only made love once or twice every
few months.'
'Well, there you have it!' The doctor said confidently...
"It's rust ."