Ten Politically Incorrect Truths About Human Nature

"4. Most suicide bombers are Muslim
Suicide missions are not always religiously motivated, but according to Oxford University sociologist Diego Gambetta, editor of Making Sense of Suicide Missions, when religion is involved, the attackers are always Muslim. Why? The surprising answer is that Muslim suicide bombing has nothing to do with Islam or the Quran (except for two lines). It has a lot to do with sex, or, in this case, the absence of sex.
What distinguishes Islam from other major religions is that it tolerates polygyny. By allowing some men to monopolize all women and altogether excluding many men from reproductive opportunities, polygyny creates shortages of available women. If 50 percent of men have two wives each, then the other 50 percent don't get any wives at all.
So polygyny increases competitive pressure on men, especially young men of low status. It therefore increases the likelihood that young men resort to violent means to gain access to mates.

[...]

It is the combination of polygyny and the promise of a large harem of virgins in heaven that motivates many young Muslim men to commit suicide bombings. Consistent with this explanation, all studies of suicide bombers indicate that they are significantly younger than not only the Muslim population in general but other (nonsuicidal) members of their own extreme political organizations like Hamas and Hezbollah. And nearly all suicide bombers are single."

Psychology Today Magazine, Jul/Aug 2007

Polygamy fueling Arizonas rate of genetic disorder

“Arizona has about half the world’s population of known fumarase deficiency patients,” said Dr. Theodore Tarby, a pediatric neurologist who has treated many of the children at Arizona clinics under contracts with the state.

[...]

“It exists in a certain percentage of the broader population but once you get a tendency to inbreed you’re inbreeding people who have the gene there, so you markedly increase the risk of developing the condition,” he said.
The community of about 10,000 people, who shun outsiders and are taught to avoid newspapers, television and the Internet, is home to the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS), a sect that broke from the mainstream Mormon church 72 years ago over polygamy.

[...]

Local historian Benjamin Bistline said 75 to 80 percent of people in the area are blood relatives of two men — John Y. Barlow and Joseph Smith Jessop — who founded the sect on the remote desert plateau in the early 1930s.
“There aren’t any new people coming in. It’s a closed door and that gene just keeps getting passed around,” said Bruce Wisan, a court-appointed accountant overseeing a trust of the sect’s assets.

Msnbc.msn.com, June 14, 2007

We actually see the same thing with Pakistani immigrants in Norway. A lot of them come from the same rural area in Pakistan, and they have been inbreeding between cousins for quite a while. Traditions are to blame.