Human behavior varies a lot. As compared with other primates, we’re heavily influenced by culture, religion, family upbringing, and so forth. As a consequence, it’s logical to conclude that our fitful monogamy is purely culturally induced and not instinctual. (On the other hand, we readily seem to

accept that promiscuous tendencies are wired into our brains.)

We are programmed to pair bond. By programmed, I mean that our brains are set up so that we engage in these behaviors with a lower threshold of enticement than we would otherwise. Italian research, for example, reveals that our racy “honeymoon neurochemistry” typically wears off within two years. Pair bonding is not simply a learned behavior. If there weren’t neural correlates behind this behavior, there would not be so much falling in love and pairing up across so many cultures. The

pair-bonding urge is built-in much like the program that bonds infants with caregivers. — psychologytoday.com