Stephanie Coontz assures us that every sexual arrangement regarded as unprecedented is old hat. Extramarital legovers and illegitimate births? Once far more common than they are today. Stepfamilies? Transhistorically, the commonplace result of high death rates and remarriages. In certain periods, divorce rates outstripped our own. Even same-sex marriages have been sanctioned in some cultures. Nothing new under the sun.

For the past few years, Coontz, a journalist and historian, has served on the Council on Contemporary Families, a collective of scholars and practitioners who compare research and clinical experience. Her fifth volume of social history, Marriage, A History, exposes the origins of an institution commonly misunderstood as a kind of genetic holding pen.

'The story that marriage was invented for the protection of women is still the most widespread myth about the origins of marriage,' she writes. 'According to the protective or provider theory of marriage, women and infants in early human societies could not survive without men to bring them the meat of mammoths and protect them from marauding sabre-toothed tigers and from other men seeking to abduct them.'

While regularly recycled to justify the sexual choices of alpha males such as Donald Trump, the 'protective' theory fails to conform to prehistoric reality. It is, Coontz writes, 'simply a projection of 1950s marital norms onto the past. The male/female pair was a good way to organise sexual companionship, share child rearing, and divide daily work ... marrying a good hunter was not the main way that a woman and her children got access to food and protection.'

The origins of marriage were exclusively pragmatic. From the earliest civilisations, the economic functions of marriage - and not romance - were most important to the middle and lower classes; the upper classes were interested only in its political potential. Coontz writes: 'One of its crucial functions in the Paleolithic era was its ability to forge networks of cooperation beyond the immediate family group or local band. Bands needed to establish friendly relations with others so they could travel more freely and safely in pursuit of game, fish, plants, and water holes or move as the seasons changed.'

For thousands of years, marriage performed the functions of today's markets and governments, organising the production and distribution of goods, creating political, economic, and military alliances, and coordinating the division of labour, as well as orchestrating rights and duties concerning everything from sexual relations to inheritance. Passion was seen as improper within marriage, a kind of perversion or aberration.

Amor vincit omnia? Defying stupid, callow or opportunistic parents in the 16th and 17th centuries carried severe social consequences. Estrangements, the disowning and disinheriting of children, even the neighbours joined in: 'Villagers might also engage in ritual harassment of the offending couple. These rituals, called charivaris, or 'rough music', were boisterous, obscene, humiliating, and sometimes painful ways to punish people who violated community norms.'

Such norms have always been a movable feast. Idealisation of female chastity began to mount in 18th-century England and by the 19th century, wives and mothers had been effectively desexed by a coy and vicious sentimentality. Certain historians argue that such ideals were a front, a justification for male dominance at a time when overt patriarchy and absolutism were unacceptable. Coontz writes:

'The cult of female purity offered a temporary reconciliation between the egalitarian aspirations raised by the Enlightenment and the fears that equality would overturn the social order.'

Two Canadian authors recently argued that, in societies with high degrees of gender equality, birthrates fall until the culture collapses and is replaced by a society that restricts women's options in order to encourage higher fertility.

Nice try, guys. Studies show that the more traditional the marital roles, the greater the sense of entrapment. Gender scripts create discord. Coontz writes: 'The definition of men as providers and women as dependents [lays] the groundwork for outright resentment on both sides.'

The definition of marriage is expanding to include the transcendence and fulfilment previous generations sought in religious revivals. Asserting the worth of the individual (as opposed to inherited wealth or political advantage), love-based marriage celebrates both tenderness and freedom of choice. The evidence? As of 2002, 'more than two million working fathers were providing the primary child care in their families while their wives were at work'.

Marriage, A History is not the product of a sensibility as succulent as historian and broadcaster Simon Schama's, but a reliquary of critically important facts.