So, females may form tight social bonds to seek out friends in times of stress. Research by Taylor and Repetti has found that during times of stress, women typically spend more time tending to vulnerable offspring while men were more likely to withdraw from family life. Oxytocin, a female reproductive hormone typically involved in pair bonding and endorphins, proteins that alleviate pain, are hypothesized to be the biological mechanisms by which we tend and befriend. From this area of research, Taylor wrote "The Tending Instinct: Women, Men, and the Biology of Relationships"