A womb's solution to male sibling rivalry?

A Canadian study reported that boys with more older biological brothers tended to be gay.

Previous research had revealed the more older brothers a boy has, the more likely he is to be gay, but the reason for this phenomenon was unknown...
Professor Anthony Bogaert from Brock University in Ontario, Canada, studied 944 heterosexual and homosexual men with either "biological" brothers, in this case those who share the same mother, or "non-biological" brothers, that is, adopted, step or half siblings.
... the link between the number of older brothers and homosexuality only existed when the siblings shared the same mother.
The amount of time the individual spent being raised with older brothers did not affect their sexual orientation.

One report contained a conservative objection:

Tim Dailey, a senior fellow at the conservative Center for Marriage and Family Studies disagreed...
“If it is indeed genetically based it is difficult to see how it could have survived in the gene pool over a period of time,” Mr. Dailey added.

It takes a bit of imagination. For instance, here's a simple hypothesis to consider: a reduction in sibling rivalry for large broods. A gay brother is less likely to fight a heterosexual brother for access to fertile females. Since males are capable of impregnating many females, there is little penalty for reducing net male fertility.

Market forces and female infanticide

Recently, it was reported that a scarcity of women in India has resulted in wife rental:

According to reports, prompted by a shortage of eligible single women, some poverty-stricken husbands in western India have gone to the extent of renting out their wives to other men on a monthly rate.
The local newspaper the Times of India reports that one man allowed his farm laborer wife, and mother of two, to stay with her boss for 8,000 rupees (175 dollars) a month. Many poor families and middlemen have also cashed in on the shortage of women by selling off their daughters to men in Gujarat, one of India's wealthiest states.

I wonder how long before girls are considered a long-term investment. With regard to societal change, perhaps this ongoing scarcity will result in the end of the traditional dowry that made daughters an economic liability instead of an asset.

Suicide bombing as motivated cognition

According to University of Toronto sociology professor Robert Brym, revenge motivates suicide bombers.

Contrary to what most academic research has shown, says Brym, "revenge and retaliation seem to be the principal animus driving this suicide bombing campaign. We see this when we examine when attacks occur, what people say about why they're taking place and when we look at the actual costs and benefits gained."
Brym and his research team created a database of collective violence events that occurred during the second intifada, the term generally used to describe the Palestinian uprising against Israel that began in the fall of 2000. The team collected data on 138 attacks from existing databases, Hebrew and Arabic newspapers and the New York Times. They then mined the database for 128 variables, examining individual motives, organizational rationales and events that led up to each attack...
By examining statements made by bombers, their families or representatives from organizations they claimed to be working for, the authors found that attacks were not generally governed by a strategic logic, as is often believed to be the case, but were motivated by a desire for revenge. By examining events that preceded each specific attack, they found that particular Israeli actions such as killings prompted most attacks. "For the most part," they write, bombers "gave up their lives to avenge the killing of a close relative, as retribution for specific attacks against the Palestinian people or as payback for perceived attacks against Islam."
Even at the organizational level -- when attacks were organized by groups like Hamas -- where strategic concerns might be assumed to be more common, six out of ten rationales focused on avenging specific Israeli actions...
This suicide bombing campaign simply isn't working in the sense that the Palestinians are not realizing any strategic gains as a result, says Brym. On the other side of the conflict, he says, "Israeli acts of oppression are also counter-productive...
"From a utilitarian point of view, the conflict is irrational. It doesn't bring about intended results for either side. The idea of laying blame on one side or the other doesn't get us very far, analytically speaking. Unless it's understood as an interaction, it can't be understood fully -- or resolved."

I blogged in 2004 on research indicating that suicide bombers are not insane, but motivated by revenge. Given that humans appear to have a neurological mechanism that rewards a desire for revenge, the next operational question I'd like answered is what specifically triggers revenge. What cultures and contexts promote the expression of revenge?

Jessica Stern makes an interesting comment with regard to anger and humiliation:

One way to summarize the distinction that helps us understand Al Qaeda is to say that bin Laden's objectives are really expressive, not instrumental. Those groups that have set instrumental objectives are not going to carry out catastrophic attacks, because such attacks will never achieve those objectives, whereas groups that are expressing anger can continuously change their mission statement. If you have a broad one, based on rage, one day you can say that it's to force U.S. troops out of Saudi Arabia. The next it can be about Iraqi children. The third day it can be about the Palestinians. That's a way to appeal to a much wider public.
Another thing about expressive terrorism is that it enables cynical leaders to attract youth who feel humiliated, culturally or personally.

Further research into terrorism and motivated cognition would appear to be a promising avenue. On a side note, consider how motivated reasoning may apply to the rationalization of terrorist acts. In other paradigms, religious correctness may be another validity metric used in evaluating what acts are permissible and what are not.

In an influential review, Ziva Kunda (1990) summarized several decades of research supporting the role of motivation in cognitive processes such as decision-making and attitude change. She claimed that motivation has been shown to affect reasoning in a number of paradigms, including cognitive dissonance reduction, beliefs about others on whom one's own outcomes depend, and evaluation of scientific evidence related to one's own outcomes. Her analysis of this research led further to the conclusion that motivated reasoning is only possible when the individual is able to generate apparently reasonable justifications for the motivated belief; this happens, however, outside of the person's conscious awareness. This is achieved via bias in accessing, constructing, and evaluating beliefs.