Classic Poem

You mustn't smile when I stroke your hair,
not yours to be proud of, this hair isn't yours:
If your mother hadn't liked your father,
your two grandmothers your two grandfathers,
your four great-grandmothers your four great-grandfathers,
your eight great-great-grandmothers your eight great-great-grandfathers:
Well,
when you grow up,
and you like a boy,
and you two grow down,
you two have a child,
and that child a child,
child a child,
child a
great-great-great-great-great-great-grandchild:
Well, what are you smiling at now?