Andrew Gelman wrote on Tuesday: "I like Sailer's theory--which is why I featured it in our book--partly because it fits into another fact we emphasized, which is that the much-remarked-upon red-state, blue-state, rich-state, poor-state pattern of Democrats in the coasts and Republicans elsewhere is relatively new, having arisen in the past thirty years or so, with the key transition occurring during the brief period from 1980 to 1992."

Consider the two most important states in the Electoral College. California voted Republican in nine of ten Presidential elections from 1952 through 1988, but has gone solidly Democratic in the five contests since. In contrast, Texas had been a swing state in Presidential elections, voting for JFK in 1960, LBJ in 1964, Hubert Humphrey in 1968, Richard Nixon in 1972, and Jimmy Carter in 1976. Texas, though, has now voted Republican eight straight times.

Why the change?

There are many popular theories for this. Most are designed to appeal to either Democrats or Republicans, with explanations often invoking either the Southern racism of Texans or the Hollywood decadence of Californians.

Having lived in both states, I have developed a much more boring theory based on geography: California ran out of its best real estate, while Texas still has plenty of its typically mediocre land. So, housing prices in California got extremely expensive (even before the Housing Bubble of 2004-2007), while they stayed affordable in Texas. And that has had far-reaching social, cultural, and political consequences.

In California, proximity to the Pacific Ocean means a superb climate, so the land between the beach and the coastal mountains is now either extraordinarily expensive or hopelessly encumbered by environmental restrictions on development. In Texas, proximity to the Gulf of Mexico means humidity and hurricanes, so Texans mostly congregate around inland cities in the gently contoured and well-watered (but rather boring-looking) Eastern half of the state.

During the Golden Age of Suburbanization (very roughly 1920 through 1980), the private automobile made the cost of land a relatively small part of the cost of a house, even in the narrow Mediterranean climate zone of California. Before cars, it was worth paying a lot to live fairly near your job because commuting by buggy was time-consuming. With a car, however, huge expanses of land became accessible by homebuyers.

Thus, when buying a house in Southern California up through about 1975, you mostly paid for the replacement cost of construction of your house because there was such an abundance of flat empty dirt all around you, ripe for development.

From the mid-1970s onward in California, however, land prices rose as suburbanization started to bump up against topographical and political limits. For example, in 1977, I recall, Los Angeles's suburban San Fernando Valley still had a few hundred acres of farmland left in its extreme northwest corner of Chatsworth, but that was soon paved over. All further conversion of farmland to backyards had to take place in distant exurbs on the far side of sizable mountain ranges.

In addition, in California, the home of the Sierra Club, the environmental movement was increasingly enlisted by existing homeowners in their fight against increased development and density. In Texas, in contrast, environmentalism never was as popular, in part because the natural environment didn't arouse as much enthusiasm. Texas just isn't as beautiful as the best parts of California.

In the 19th Century, when Americans moved farther out toward the frontier, they often disassembled their houses and took the pieces with them. Land was cheap, but nails were expensive. Around 1980, you started to see the opposite phenomenon in California: the tear-down, in which a perfectly good house was thrown away because the land had become so expensive. For example, when Ronald Reagan sold his very nice house in the Pacific Palisades neighborhood between Santa Monica and Malibu to move into what he jokingly called "government housing" in Washington in early 1981, the new owner demolished the President's old home and replaced it with a mansion more suited to the now extremely valuable land.

This restriction of supply, combined with increases in demand from immigration, easier mortgage credit standards, and the like, set off a rise in California home prices that lasted from 1976 through 2006, topping out at heights that would have seemed insane in 1976 (and that seem fairly nuts from the perspective of 2009).

I don't want to sound like a total Malthusian, but the relationship between population density, land prices, age of marriage, and number of babies was pointed out by Benjamin Franklin in 1751, 47 years before Malthus wrote. (Malthus gave Franklin credit in his second edition). In the founding document of American social science theorizing, "Observations concerning The Increase of Mankind," Franklin pointed out, with an 18th-century surfeit of capitalization, "For People increase in Proportion to the Number of Marriages, and that is greater in Proportion to the Ease and Convenience of supporting a Family. When Families can be easily supported, more Persons marry, and earlier in Life."

In the American colonies, a limited population led to both low land prices and high wages, which made affordable early marriage, which led to abundant children. In contrast, "Europe is generally full settled with Husbandmen, Manufacturers, &c. and therefore cannot now much increase in People. Land being thus plenty in America, and so cheap as that a labouring Man, that understands Husbandry, can in a short Time save Money enough to purchase a Piece of new Land sufficient for a Plantation, whereon he may subsist a Family; such are not afraid to marry." Franklin concluded, "Hence Marriages in America are more general, and more generally early, than in Europe."

The Industrial Revolution lifted the Malthusian limit on population, but the cost of land never quite ceased to influence decisions to marry and have children. As America's coastal regions filled up, affordability of family formation began to differ sharply from state to state. In 2005, the median Dallas home only cost 2.8 times the local annual income, while the median Los Angeles home cost 12.7 times what the median Angeleno was making.

As Franklin noted 258 years ago, people in expensive locales tend to delay marriage and have fewer children. The 2000 Census found that 18-44 year-old non-Hispanic white women in California were less likely to be married and had fewer babies than their counterparts in Texas. And the culture follows along. GOP campaigns on "Family Values" sell better in states where more voters have spouses and children.

Indeed, the Marriage Gap is much more potent in influencing voting than the celebrated Gender Gap.

Democrat pollster Stanley Greenberg's report "Unmarried Women in the 2004 Presidential Election" found that:

"Unmarried women voted for Kerry by a 25-point margin (62 to 37 percent), while married women voted for President Bush by an 11-point margin (55 percent to 44 percent)...

This was true of all age groups... Unmarried 18- 29 year olds gave Kerry a 25 point margin, while younger married women, like their older counterparts, gave President Bush an 11 point margin."

Greenberg built a multiple regression model of the exit poll results and found:
"Marital status was a statistically significant predictor of likelihood to vote for Kerry...This is true even when controlling for other demographic and behavioral factors such as gender, age, race, gun ownership, union household membership, party identification, education, income, and church attendance.

"Controlling for all these other variables, the odds of voting for Kerry were 1.56 times greater if the voter was unmarried than if the voter was married.

"In contrast, once other demographic and behavioral factors were controlled for, a voter's gender had no significant effect on their likelihood to vote for the Democrat." [Italics are Greenberg's.]

Thus, in 2004, Bush carried the 26 states with the least home price inflation since 1980.

As I said, mine is a rather boring theory that sees the political differences between the two biggest states not as originating in the innate horridness of one kind of people or another, but as the natural outcomes of natural differences in geography.

Still, political strategists ought to be able to come up with some interesting ideas based on my perspective.