One of the big blind spots in American demography is religion. We have excruciatingly detailed demographic statistics the slice and dice the American population based on race, Hispanic origins, sex and age, mostly from a variety of government sources. We have far less information on religion, pieced together from a mix of eclectic private sources.
Religion As An Ethnic Marker
One result of this is that non-Hispanic whites, the plurality ethnicity and Hispanics, another large census ethnic category, look monolithic. This also heightens stereotypes about immigrant populations.
Of course, broad categories like "non-Hispanic white" or "Hispanic" are social constructions. Many people who are part of today's "non-Hispanic white" plurality, would have been considered a non-WASP minority a century ago. A Pentecostal mestizo Hispanic family from Oaxaca, Mexico may look demographically very different from a white Catholic family from Buenos Ares, Argentina with distant ethnic roots in Germany, even though both are lumped into the category of Hispanic by census definitions, in much the same way that a third generation Japanese American family may look very different demographically than a first generation refugee family from Vietnam, even though both would be considered Asian for statistical purposes.
Immigrant populations, generally, differ significantly in religion from their home countries. Immigrants from places with predominantly non-Christian populations, such as the Arab world, are much more likely to be Christians than the general populations there, in part due to religious freedom driven immigration, and in part due to missionary facilitated ties to the United States. Latin American immigrants are much more likely to be non-Roman Catholics than the general population of their Latin American homelands. Immigrant populations also tend to be more religious, generally, than domestic populations, largely because religious institutions provide cultural havens.
The biggest political and cultural divide in the non-Hispanic white population of the United States is roughly mirrored religiously, with conservative Christians on one end of the spectrum, Roman Catholics in the middle, and mainline Christians, non-Christian, and secular whites on the other. While people don't stick as steadfastly to the religion of their births as they once did, religious affiliation provides useful way for a demographer to operationalize social class divisions among non-Hispanic whites. Statistical data on college entrants suggest that the link between social class and religion for non-Hispanic whites remains strong.
The Mormon Social Model
Religious demographics also provide a way to gauge the degree to which religion actually changes how people live. Mormons take the cake in this department. Members of the Church of Jesus Christ of Later-Day Saints are more distinct demographically from the general non-Hispanic white population than almost any other large religious denomination in the nation. Few other religions come closer to offering an alternative total life script than the Mormons. In contrast, your typical Episcopalian is likely to live a life not very different from a typical non-religious American.
Part of this is a consequence of geography that makes it easier to measure the distinctions. Just about everything that is demographically distinct about Utah can be attributed to the impact of the LDS church, which counts 70% of Utah's population as adherents, but is much less common in the rest of the United States. But, the geographic concentration itself is to a great extent a historical legacy of an effort to create a distinct society. It combines social outcomes that policy makers tend to think of as impossible to have together in the mainstream social model, like young marriage ages and low divorce rates.
The Mormon model offers a lot that the rest of the nation would like to emulate. For example, stable marriages, high levels of education, low levels of child poverty, high levels of private charity, a strong civil society, low abortion rates, low levels of out of wedlock births, low levels of suicide, and low levels of the public health problems associated with alcohol and tobacco (are there any public health problems associated with caffeine consumption?).
There are, of course, other element of the model about which the nation is not favorably inclined or ambivalent. For example, large families, early marriages, high levels of intense (and heterodox) religious belief, and high bankruptcy rates.
Many of the demographic consequences of the Mormon social model are largely not severable from each other. Early marriage and low out of wedlock birth rates, for example, go hand in hand in the Mormon social model. Intense religious belief drives the willingness to break from the national social norms about alcohol, tobacco, marriage and childbearing. Large families create the economic interdependencies that help make marriages more stable, and can be a factor in making bankruptcy necessary in hard times.
A glance of the interdependencies of the Mormon social model makes it easy to understand how modernizing leaders in the Third World, like Ataturk, chose to keep not only functional parts of colonial culture, but also dysfunctional ones like Western fashion conventions. Culture is a package deal and the linkages between different parts of the package are often non-obvious. For example, while low alcohol consumption is a key to Mormon public health, high alcohol consumption is central to making the rich French diet less of a health problem for the French. According to Malcolm Gladwell's book Outliers, culture is key to explaining commercial aircraft accident rates and transitioning South Korean flight crews to English was the lynch pin necessary to reduce commercial aircraft accidents on Korea Air.
It is also worth noting that while the Mormon social model has always been distinct, different parts of it has been more notable at different times. For example, Mormon family patterns look a lot like those of typical American families in the Baby Boom. But, low levels of tobacco use among Mormons is now much less out of step with the general social norms of the United States than it was in the 1950s.
Are Mormon boys more likely to be gay?
One wonders absently if strong opposition to gay rights (Mormons were pivotal players in the fight over Proposition 8 regarding gay marriage in California and have been a major driving force in the anti-gay stances of the Boy Scouts of America) has anything to do with the hypothesis that boys with more older brothers are more likely to be gay, and that large families are much more likely to have boys with older brothers than other families. If the hypothesis is correct, gay men are disproportionately Mormon. Proponents of the hypothesis estimate that the fraternal birth order effect accounts for approximately one seventh of the prevalence of homosexuality in men. But, given the relatively small percentage of non-Mormon men who have multiple older brothers (particularly now that total fertility rates among native born Roman Catholics has fallen), a fraternal birth order effect would be excepted to account for a much larger share of the prevalence of homosexuality in Mormon men. Above average rates of of homosexuality could also help explain the attraction of polygamy in the early Mormon church (a doctrine abandoned in a bargain for Utah's statehood in the early Mormon church and later internalized into the doctrine of the largest (and dominant) Mormon denominations).
Likewise, this effect could help explain both the past importance of the celebate Roman Catholic clergy and the current shortage of clergy in the Roman Catholic Church as birthrates declined (i.e. the celebate clergy may have offered a particularly attractive life choice of young gay Roman Catholics who may have been more common when family sizes were large).
The fraternal birth order hypothesis is nowhere near definitively established. And, it isn't hard to imagine countervailing forces. For example, even if fraternal birth order matters, if genetics is another important factor in the likelihood that someone will be homosexual, and the Mormon church is not a gay friendly environment, gays may be much more likely to convert to the LDS faith (for which conversion is an important growth driver) and more likely to leave the faith if they are born into it. In a few generations (and Mormon generations are shorter than the national average), even a modest tendency in this direction could overshadow birth order effects if homosexuality has a strong genetic component. Maybe, someday, when we know a little more about the biology of human sexual orientation we may be able to answer these questions.