Monogamy is a practice characterized by only having a single partner at any given time, in contrast with polygamy, where people may have multiple partners. This practice takes a number of different forms in the human and animal world and in the early 2000s, some significant scientific studies changed the way people thought about monogamy. Among humans, having only one partner is generally believed to be preferable and desirable, although there are some communities where this is not necessarily the norm.
In true sexual monogamy, people only have sex with one other person. This may be for life, or it may be in the form of serial relationships, with people moving through a series of sexually exclusive relationships. Having only one sexual partner is believed to be an important part of marriage in many cultures, and having sexual relationships with people outside a marriage can be grounds for divorce or the breakup of a relationship.
Social monogamy involves forming a connection with someone to share resources, engage in sexual activity, and raise children together. It often involves sexual exclusivity as well, but this is not always the case. Social monogamy isn't exclusive to humans; many bird species previously believed to be sexually monogamous have since been revealed as socially monogamous. They form attachments with mates, but may have sex with other birds. In some cases, they even bear young with these outside partners.
There are various biological and social advantages to only having one partner for some species that play a role in determining whether species as a whole opt for monogamous relationships or other types of arrangements. Genetics also appears to play a role. In species with a long history of monogamy, genes appear to code for rewards for organisms that form lasting and exclusive bonds with just one other organism. In these organisms, neurotransmitters that stimulate the reward areas of the brain are emitted during interactions, especially close physical ones, with monogamous partners.
Historically, the belief that people should only have one sexual partner at a time has played an important role in many human societies. It is common for rules of inheritance to follow patrimonial lineage and in many cultures monogamy among women in particular was deemed of great importance so that men could be assured that the children in their marriages were their own. The valuing of monogamy also contributed to the social attitudes that surround marriage and other types of human relationships. Humans also appear to be among the species that have some genetic predisposition to monogamy.