Sexual dimorphism in human bonding refers to the sex-based differences in how humans form, maintain, and experience social and emotional bonds, including romantic partnerships, parent-child relationships, friendships and broader social connections. These differences encompass variations in attachment styles, hormonal response patterns, neural processing of social information and behavioral expressions of intimacy and connection. They also relate to human approaches to handling fear and stress. At a very basic level, differences between bonding in men and women originate in the fact that humans are born defenseless and require a great deal of parental investment to survive to sexual maturity, especially in the ancestral environment. The differing male and female roles in providing this investment are said to have conditioned their different bonding "styles" over the course of evolutionary history.