Pennsylvania State University professor Philip Jenkins is a man to be taken seriously. One of America's most thoughtful academics, he is a deep thinker. Two of his books in particular, The Next Christendom and The New Faces of Christianity, are landmark works. In a recent issue of the New Republic, Jenkins makes an intriguing proposition: that the demographic profile of Iran might make the Islamic republic into the "Denmark of tomorrow."

This would be good news. The Middle East could use a Denmark or two (or seven). But an examination of Jenkins' predictions and the history of fertility and demographics suggests that he may be mistaken.

Jenkins makes essentially the following case: Iran has been experiencing a giant decline in fertility rates, from more than 6.5 children being born per woman 30 years ago, to a rate of 1.71 today. This puts Iran below the all-important 2.1, the rate needed to keep population constant. Unless matters change, Iran will begin to experience a population decline within two generations.

No prob, says Jenkins. Population decline, he believes, could "usher in a new era of stability," creating "an Iran that is bourgeois [and] secular." To support this thesis, Jenkins notes that high-fertility nations include hot spots such as Iraq, Somalia and Sudan, while low-fertility nations include countries such as Italy, Germany and Japan.

Jenkins then notes that declining fertility rates lead to smaller extended families, and hence to an increased reliance by the elderly on state support. In the future, he argues, Iranians will be "invested in the state's continued stability." He also sees the lower fertility rate as a boon to Iranian business: "With fewer heirs, you are more likely to spend money on yourself; increased spending buoys the economy; and, suddenly, industry is buzzing away."

Finally, Jenkins argues that the presence of fewer children in Iran will weaken communal, and hence religious, ties, promoting secularism and even helping to make Iranians "more accepting of people who seek options outside of traditional marriage" - by which he means same-sex marriage.

Jenkins ultimately may be right in his assessment, but his reading of the Iranian fertility bust is, at best, optimistic. It seems much more likely that Iran's demographic implosion will lead to instability, conflict and economic collapse.

Let's look first at the structure of Iran's population. With Iran's fertility rate dropping, it currently has what is known as a "youth bulge." Its median age is 25.8, and 23 percent of its males are under the age of 15. The German demographer Gunnar Heinsohn makes a compelling case that such bulges of young men lead historically to military conflict.

But this will be Iran's final youth surplus. By 2050, 30 percent of Iran's population will be composed of elderly dependents, and a dwindling number of younger workers will be forced to support them at their own expense. In wealthy First World countries such as Denmark, this situation leads to discussions about pension benefits and taxes. In poor, developing countries such as Iran, it could well lead to unrest and instability. It is one thing to be old and rich; being old and poor is quite another.

And Iranians have little hope of becoming rich. Oil is, far and away, Iran's leading industry, but its exports are diminishing every year. As soon as 2020, Iran may no longer have an oil-export business. Oil makes for 80 percent of Iran's exports today, according to the CIA World Factbook; the other leading exports are "fruits, nuts and carpets." Its only industries of note are textiles, cement and food processing. Oil revenues equal roughly one-fifth of all personal income in Iran. Once oil disappears, it's unclear how happy, childless Iranian couples will have money to burn. Certainly, no industries even exist in Iran to begin "buzzing away."

Already, Iran's economy is fraying at the seams. In 2002, 40 percent of the population was below the poverty line. The Iranian government's own (rosy) projection puts unemployment at 15 percent (it is likely twice that, and even higher among the volatile youth cohort). Inflation was 12 percent in 2006 and has, by all accounts, risen since.

Iran's government seems to understand the long-term implications of its demographic situation, which is why President Mahmoud Ahmadinejad has relocated millions of people from rural villages to cities, where they can be controlled more easily. He has also introduced more comprehensive social services. To be sure, this is an attempt at stability, of a sort. Some would call it a strengthening of authoritarianism.

That's the short-term outlook; the medium term is more unsettling. From a geostrategic perspective, Iran must understand that its weak position will become progressively weaker, leading to ruin. Its only hope lies in the prospect of expansion: Southeast Iraq, Saudi Arabia (where Shiites dominate the oil-rich eastern region), and the United Arab Emirates all present attractive targets for Iran, with ample oil reserves and potentially sympathetic populations. Empire is Iran's most logical path to salvation.

After all, with economic ruin on the horizon, and a demographic catastrophe in progress, they have nothing to lose in a conflict, other than several million military-age young men who, if left to their own devices, might someday turn on the regime in any case. Of course, if Iran were to attempt to establish regional hegemony, it would face the wrath of the United States and the Western powers, much as Saddam did in 1990. Unless they had a nuclear deterrent. When you game it out, Iran would be foolish not to try for nuclear weapons. Its fertility rate and economic reality practically demand it.

And what about Jenkins' hope that lower fertility will, in the long run, make Iran a secularist paradise, like Denmark or Germany? As demographer Philip Longman demonstrated in his essay "The Return of Patriarchy," fertility rates do not fall uniformly across populations. They tend to dip most precipitously among secular, liberal segments, and remain higher among orthodox, religious segments. If this rule were to hold in Iran, it would mean that, in the long run, the population would become more, not less, religious, as secular families dwindle and fundamentalist families flourish in their place.

Demography, we must remind ourselves, is not destiny; but neither can we allow it to become fantasy.

-Jonathan V. Last