The abuses so often cited by opponents of polygamy - sexual, physical, subjugation - are certainly not unique to multiple marriage, an expert testified Wednesday at a landmark B.C. court case examining Canada's ban on the practice.
Those abuses are found in all forms of marriage, not only those with multiple wives, said Oakland University's Todd Shackelford, an evolutionary psychologist whose work focuses on male aggression within marriage.
Prof. Shackelford was called to refute testimony that inevitably leads to physical and sexual abuse, the subjugation of women and familial conflict.
"I have been focusing my research on some of these many negative consequences in monogamous relationships, including men's violence, psychological, physical and sexual aggression against their partners," Prof. Shackelford said.
"In every such mating relationship - indeed in any sort of relationship - you will find there is conflict. … Polygyny [polygamy in which a man has multiple wives]doesn't have the market cornered on some of these negative consequences."
A week earlier, another evolutionary psychologist, Joseph Henrich from the University of British Columbia, testified that polygamy lowers the age at which girls marry, increases the age gap between husbands and wives and produces a pool of men who are unable to find women to marry. He said that, in turn, leads to higher rates of domestic violence, encourages men to exert control over women and increases crime.
But Prof. Shackelford said Prof. Henrich was simply using data from monogamous marriage - including from Prof. Shackelford's own research - and guessing those same problems would be amplified in polygamous societies.
"My overall comment is that Prof. Henrich has not provided any direct evidence of statistic comparisons of the risks for these various negative outcomes in polygynous marriages, as compared to monogamous marriages," Prof. Shackelford said.
"And I do question whether it's a reasonable assumption that what you find in the context of monogamous relationships can be applied full force and without regard to any potential cultural differences in polygynous relationships."
For example, Prof. Henrich told the court, women in polygamous marriages might treat the children of their so-called sister wives poorly, because they aren't biologically related to them.
Prof. Shackelford acknowledged there is research that shows stepmothers and stepfathers in monogamous marriages are more likely to neglect or even physically abuse their stepchildren, but he cautioned against applying that to polygamous societies.
"Given what we know, there may be some pressure on these co-wives in this cultural context to actually attempt to get along better, to treat one another's children in a way that is in the best interest in the children," he said.
B.C. government lawyer Craig Jones suggested it's irrelevant whether abuse also occurs in monogamous relationships. Rather, he said, the real issue is whether it occurs more in polygamy.
"We might say that drunk driving causes a certain set of harms - broken bones, deaths and so forth - and we might also say that sober driving causes those very same harms. The question, though, is: does drunk driving cause more of the harms?" Mr. Jones said.
"So it doesn't get us very far on the larger issue simply to say there are harms in monogamous relationships."
The case was prompted by the failed prosecutions for polygamy of two religious leaders of the southeast B.C. community of Bountiful.
The residents of Bountiful are members of the Fundamentalist Church of Jesus Christ of Latter Day Saints, a breakaway sect of the mainstream Mormon church that continues to practice polygamy. The mainstream church renounced the practice more than a century ago.
Bountiful leaders Winston Blackmore and James Oler were charged last year with practising polygamy, but those charges were later thrown out on technical legal grounds.
The constitutional reference case is expected to hear evidence until the end of January. Legal experts have predicted the case is destined for appeal all the way to the Supreme Court of Canada.
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