Such couples had an evolutionary advantage in producing offspring who would themselves be successful as parents.

There was a time when archaeologists thought that our ancestors evolved from lone hunters to male/female couples and then to mixed sex groups with undifferentiated roles and then to what are here called villages.

[See] [How Humans Became Social] "Researchers have long believed that it was a gradual process, evolving from couples to clans to larger communities. A new analysis, however, indicates that primate societies expanded in a burst, most likely because there was safety in numbers."

In that Tarzan/Jane view of our past, survival of the female would simply not have been possible in the absence of a strong emotional bond and strong provider/protector instincts in the male.