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