The metaphor of a ticking clock is often used to refer to a woman's growing urge -- from puberty onwards to menopause -- to conceive before her childbearing years are over. New research shows that there's more truth to this phrase than you might think. "The very subtle sound prime of a ticking clock changed the timing with which women sought to have children and the traits they sought in potential partners -- both central aspects of women's mating-related psychology," says one researcher.