n social anthropology and sociobiology, polyandry (Greek: poly- many, andros- man) refers to a form of polygamous marriage, or other sexual union, in which one individual is married to two or more husbands at the same time. Polygyny, on the other hand, refers to polygamy in which one man is married to two or more wives. The form of polyandry in which two (or more) brothers marry the same woman is known as fraternal polyandry, and it is believed by many anthropologists to be the most frequently encountered form.
It is the harvesting season and Kundol Lama and her family are pulling up radishes in their small field above a river gorge in remote north-western Nepal. This is rigorous work, but Kundol has a little extra manpower at her disposal. She has two husbands, Tsering Yeshi and Pema Tsering, who are brothers.
When they have filled the baskets to overflowing they sling them on their backs and climb the steep hillside back to their village, Barauntse. Almost every household here is polyandrous - meaning that the family's sons have jointly married a sole woman.
Tsering Yeshi is a farmer, while Pema Tsering has a government job. Their wife says polyandry works well in this beautiful but harsh land. "My husbands can take it in turns to go out for business, so I'm happy," she says. "If there were only one, he'd be under pressure to go out and trade, and there'd be no one to help at home." They have three children between them. As in most polyandrous households, although they know who belongs to which father, the distinction matters little.
Pema Tsering, the younger husband, says polyandry gives natural population control to this community, who are Buddhists. He says that in the neighbouring Hindu culture, "there's only one husband - if he dies, no one cares about the wife and it's difficult for the children as well".
But polyandry nowadays is rare. It survives in Nepal in a few ethnic Tibetan communities such as this one, who are called Lamas.
Even in remote Barauntse, polyandry is struggling to survive
Tsepal Lama, who runs a guest house in the nearest town, Simikot, is in a monogamous marriage but spells out polyandry's advantages.
He believes it developed because the highland Lamas lacked cultivable land, and with polyandry "the land is not divided among the brothers".
It also worked well where there was a division of labour between brothers - one to look after livestock, one to work in the fields, and one to travel for business or traditional trades such as Nepalese rice for Tibetan salt.
Even in Barauntse, however, polyandry is struggling to survive.
The family of Tsering Mutup Lama, 38, has seen great changes.
My brothers' friends tease them that the tradition is old-fashioned
Tsering Mutup Lama
As the eldest of five sons, he was the one involved in the marriage ceremony to wife Kema; the younger four were also deemed to be married to her, but two have since broken away and remarried.
The youngest two, one of whom is only 17, are currently studying in Kathmandu and it is uncertain whether they will rejoin the household.
Tsering says one reason for the two brothers breaking away was that they were forced to sell their livestock and had to move further away for work.
This happened when new laws barred them from access to previously communal grazing lands.
Kema says big age differences can complicate family relations
"Once the sheep were sold they had nothing to do - all they did was sit at home and eat," says Kema, laughing a little.
She says such change has also arisen from people having a wider choice of jobs and education.
Neither Kema nor Tsering begrudges the two brothers their new separate lifestyles.
But Tsering is hurt by many Hindus' attitude to polyandry. "My brothers' friends tease them that the tradition is old-fashioned," he says.
Villagers were at first highly reluctant to talk to the BBC, saying that in the recent past journalists have visited this community from Kathmandu and abroad and sought to ridicule the custom.
Kema also says that where there is a big age spread among the brothers, family relations can be ambiguous. She says the two youngest ones feel more like younger brothers to her than husbands.
In Simikot, a couple of valleys away, there are numerous people who have broken away from polyandrous arrangements.
In Simikot, many have broken away from polyandrous marriages
Mutup Lama, 41, a porter and farmer, did so mainly because of age. He and his older brother originally shared a wife in a village, but she was the same age as his brother - 14 years older than Mutup.
After coming to Simikot and finding a new wife, he abandoned all his land and animal rights, he says.
"We're happy and we have two children," he says, but adds that this monogamous life is more of a struggle financially.
This age factor is not always a problem.
A 22-year-old man in Barauntse, Chakka Lama, told the BBC he was absolutely committed to the wife, 10 years older, whom he shares with his one younger and two older brothers, even though he cannot even remember the marriage ceremony.
But polyandry is definitely under pressure. This is because of not only economics and education but also the simple spread of more romanticised ideas of marriage.
Not only that - there have been reports of Maoist rebels, who are powerful in this area, speaking out stridently against the system. They have also recruited some husbands to their ranks.
"I think that within 10 or 15 years the system will completely disappear," says one villager sadly.