Humans are polygamous by nature and faithfulness is only an unnatural impulse, claims a new book.

In the new book, Sex at Dawn: The Prehistoric Origins of Modern Sexuality, authors Christopher Ryan and Cacilda Jetha, pore over anthropological, anatomical and psychosexual evidence, arriving at a bleak conclusion-our rabid sexuality just doesn't gel with monogamy.

That's because we weren't a dutifully faithful species until the advent of agriculture, at the most 2,000 years ago, claim the husband and wife team.

Before that, people evolved in "primal hordes" where food, shelter, childcare - and sex - were shared.

Men didn't care about paternity because they had no private property to pass down, and women got all the resources they needed from their community, not individual men.

That dynamic resurfaced with the original American swingers - not hippies, but crewcut Second World War air force pilots swapping wives at key parties.

If a husband was killed overseas, the surviving pilots would, in theory, take care of his wife.

'Of all Earth's creatures, none is as urgently, creatively and constantly sexual as Homo sapiens," the Globe and Mail quoted the authors as writing in the book.

Our bodies offer even more clues to our promiscuous origins, from women's capacity for multiple orgasms to men's penises, the largest of all in the primate order.

Still, the authors lament, monogamy persists as the norm even as high divorce rates, a burgeoning hook-up culture and a porn industry grossing some hundred billion dollars annually declare our randy dispositions. (ANI)