AEI has released an interesting paper examining world-wide population trends. I'm still absorbing it so I will just point out a few things that jumped out at me, and leave comments on it for a future time or for GC or Razib.

Unnatural Gender Imbalances;

And the collision is not only happening in East Asia. Gender determination technology is now nearly universally available; sub-replacement fertility is fast becoming the planetary norm; and a strong son-preference has been expressed in a number of cultures worldwide. One of these is Punjab, India. In a major survey undertaken there a decade ago, when fertility levels were still well above replacement, ten times as many women expressed a preference for a boy as for a girl. And according to India's latest census, in that state's youngest age groups, there were 126 young boys for every 100 young girls. That figure cannot be taken as an exact indication of gender imbalance at birth: differential mortality and/or migration, for instance, may have affected this reported outcome. Yet the true sex ratio at birth in Punjab may not be far different from the extraordinary disparities reported for the very young. Contrary to expectation, with increased affluence, education, and contact with the outside world in China, the gender imbalance has increased, and it is starting to do the same in the Caucasus, parts of Latin America and Eastern Europe, and even subpopulations within the United States.

Now I knew that China and India had gender imbalances, but the U.S.?

American "Demographic Exceptionalism"
(basically we are the only developed country to not have a shrinking population)

So how can we explain this fertility discrepancy? Possibly it is a matter of attitudes and outlook. There are big revealed differences between Americans and Europeans regarding a number of important life values. Survey results highlighted in The Economist (November 2003) point to some of these. Americans tend to identify the role of government as "providing freedom," while Europeans are inclined to think of government in terms of "guaranteeing one's needs." Attitudes about individualism, patriotism, and religiosity seem to separate Americans from much of the rest of the developed world. Is it entirely coincidental that these divergences seem to track with the big cleavages between fertility levels in the United States and so much of the rest of the developed world?

Godless comments:

Without mass immigration, the US would have negative population growth (the Anglo fertility rate is 1.84, below replacement level). See also here:

Future fertility and immigration may play major roles in the Nation's growth.

The two major components driving the population growth are fertility (births) and net immigration. In the middle series, the number of births is projected to decrease slightly as the century ends and then increase progressively throughout the projection period. After 2011, the number of births each year would exceed the highest annual number of births ever achieved in the United States.

Almost one-third of the current population growth is caused by net immigration. By 2000, the Nation's population is pro-jected to be 8 million larger than it would have been if there were no net immigration after July 1, 1992. By 2050, this difference would increase to 82 million. In fact, about 86 percent of the population growth during the year 2050 may be due to the effects of post-1992 net immigration.

In the absence of mass immigration, the US population would have similar demographic characteristics to other majority European countries. I can provide more citations on this for the skeptical, but it's an accepted fact among both immigration reformers and proponents of the current system. AEI takes a much more positive view on the phenomenon than I do; their fallacious assumption is that the individuals being added to the population are not net tax recipients:

"It doesn't take a genius to figure out that education is the best predictor of income and thus of benefit and cost," said UC Davis economist Philip L. Martin, an expert on rural immigrants.

He cites studies that say an arriving immigrant with at least a high school education will pay an average $89,000 more in taxes and other revenues than he or she costs in services. Those with less than a high-school education, however, put such a demand on public services that their large negative value persists through their children's and grandchildren's generations.

Like Tyler Cowen, I believe a revenue-positive strategy rather than our current revenue-negative immigration strategy is the way to go. Welfare is not the only category of expenditure; everything from public education to roads to police officers costs money, and immigrants with less than a high school education are unlikely to pay more than they necessitate in payments. Often, immigration's effect as a whole on the tax payer is misleadingly estimated by grouping Ph.D. physicists and engineers with migrant workers. If you break them out separately as Davis and others have done, the disparity is stark - and there is no need for us to take millions of people with less than a high school education when we could be taking the smartest of the world.