Short answers, pulled from the story.
Monogamy is a relationship of two individuals in which they form a mutual and exclusive intimate partnership. The term derives from the Greek words for one and marriage, implying a singular, lifelong union, yet the practice varies wildly across cultures and disciplines.
Reproductive monogamy became more common between 5,000 and 10,000 years ago, coinciding with the Neolithic agricultural revolution. This shift occurred as formerly nomadic societies began to claim and settle land for farming, creating a vested interest in limiting the sexual activities of their reproductive partners.
Over 90 percent of bird species are socially monogamous, but genetic testing reveals that more than 30 percent of baby birds in any nest are sired by someone other than the resident male. This discrepancy challenges the notion that monogamy is a natural, unbreakable law of nature.
The median rate of non-paternity is 1.8 percent, with rates ranging from 0.03 percent to 11.8 percent in various studies. Covert illegitimacy is less than 10 percent among sampled African populations, less than 5 percent among sampled Native American and Polynesian populations, and generally 1 to 2 percent among European samples.
The Christian Church enforced monogamy because wealth passed to the closest living, legitimate male relative, often resulting in the wealthy oldest brother being without a male heir. This allowed the wealth and power of the family to pass to the celibate younger brother of the church, ensuring greater reproductive fitness for the elite.
The prairie vole serves as a key model for understanding the underlying mechanisms of pair-bonding, with behavior influenced by the number of repetitions of a particular string of microsatellite DNA. Pair-bonding behavior is connected to vasopressin, dopamine, and oxytocin levels, with receptors located along the mesolimbic dopamine reward pathway.