"When a man gets involved with a woman for any length of time, his facial hair starts to grow faster than it did before"

"Women cloistered away from men [in a boarding school, say] enter puberty later than women who are around men"

Among other oddities, all attributed to human pheromones, chemical scents that don't register consciously:

-A baby can detect its mother entering a room before the baby can see her;
-Children can sense danger while they sleep;
-Mothers of school-age children can detect a T-shirt worn by their own child;
-Fathers can't recognize the smell of their infants, though they can tell whether a T-shirt has been worn by a man or a woman.