It is the way in which humans advertise themselves in the marketplace of mates and show off their traits to a contender before jumping into a relationship. To use an analogy, flirting is to sex what window-shopping is to buying. It is a human mating dance in which we brandish our good qualities, parade our prospects, flaunt our care-giving abilities, and generally exhibit ourselves. This playful theatre is basically warming up to the 'dirty deed'. And good flirting definitely heightens attraction.
Animals do mating dances, display their plumage, fight vicious battles, and sniff butts.
Thank goodness, we flirt. Advertising ourselves to members of the opposite sex tests their availability and interest. Our flirtatious signals have been studied carefully. Both men and women will show their submissiveness and docility by shrugging their shoulders, and resting their hands with the palms facing up. A flirtatious woman will make eye contact, play with her hair, lick her lips, sway her hips, bat her lashes, and look away.