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Kody Brown and his four wives Meri, Janelle, Christine and Robyn who star in the TV series Sister Wives. TLC

A growing number of Americans consider polygamy morally acceptable, according to the latest poll.

The percentage has more than doubled since 2001, according to the results of a Gallup survey tracking opinions on moral issues since the early 2000s. In 2001, only 7% of Americans deemed polygamy morally acceptable; it's now up to 16%.

The rate of acceptance is growing the fastest among almost all other social issues Gallup tracks, including attitudes toward abortion, gambling and stem cell research. Even more intriguing is that Yanks are more accepting of polygamous marriages than of extramarital affairs in monogamous marriages.

The idea is still far from popular, but it is gaining momentum, and some supporters see a possible future when having many mates could become legal just as gay marriage is in a growing number of states, the Daily Beast reports.

Polygamy could become legal in US by 2040

Conservative New York Times columnist Ross Douthat predicted that polygamy could be legalised in the US as early as 2040 given the growing rate of acceptance.

Observers credit increased acceptance in part to popular TV series like Sister Wives and Big Love for broaching the long-taboo subject and bringing it into Americans' living rooms.

Estimates place the US polygamous population at up to 100,000 people, mostly in fundamentalist Mormon and Muslim families. But continuing concerns about the practice are linked to studies revealing detrimental impacts for women and children — including domestic abuse and pedophilia — as well as for lower-status men who tend to be shut out of marriage in polygamous communities.

The vast majority of polygamous families in the US and around the worldwide are polygynous (men with more than one wife) rather than polyandrous (women with more than one husband).

The high-profile trials of Warren Jeffs, leader of the Fundamentalist Church of Jesus Christ of Latter-Day Saints in Texas and Utah, on charges of rape and child abuse, revealed the dangerous side of polygamy.

Teenage boys stepped forward during Jeffs's trial to tell the media about being ousted from the community with little support so they wouldn't compete with older men for young brides. Jeffs was sentenced in 2011 in Texas to life in prison for having sex with under-age girls whom he took to be his "spiritual brides." Prosecutors said Jeffs took a total of 78 plural wives, including several as young as 12.