Evidence of its role in emotional attachment is relatively new. Researchers believe that oxytocin produced during nursing also helps forge or enhance a strong bond between mother and child. In lab rats and other animals, an injection of oxytocin triggers mothering instincts. Rats, for instance, start building nests and act like they are nursing. Oxytocin also makes female animals sexually receptive, and seems to influence their choice of a mate.
Female animals show little interest in males until injected with oxytocin.
Days or weeks later, she tends to pick it out as a mate when exposed to a group of males. Oxytocin levels increase during touching, cuddling, and other early stages of sexual activity, and peak at orgasm. In women, the theory goes, the combination of oxytocin and female hormones like estrogen forge an emotional attachment with a partner. In men, the bonding effect is muted, due to the male's higher testosterone levels. As a result, men form emotional ties slower, and are more likely to regard initial sexual contact as just sex.