It is one of the most worrisome economic statistics of a year that was full of them: In 2021, according to the Census Bureau, the U.S. population grew at the slowest rate in recorded history.

This poor performance was due to slowing immigration, low birth rates, and of course a high number of deaths from COVID-19. Total population grew by just 0.1%, or 392,665. Even measured in absolute terms, that increase is smaller than during the confluence of World War I and the Spanish flu pandemic.

Inflation and unemployment rates get a lot of attention, justifiably. But this macroeconomic news ought to be of at least equal concern. That’s because — in economies as well as careers — what’s important is not only the level of achievement but also the momentum. The goal is to have a series of ascending successes pushing you toward successively stronger positions.

For all its flaws, the United States is a marvelous collection of invented and evolved institutions. It took a lot of work to get here. At the margin, it costs relatively little to allow more people to enjoy and benefit from America’s Constitution, its favorable business environment and its nuclear umbrella. In the terminology of economics, the U.S. is a public good. Allowing more people in the country is like allowing more people to fill the empty seats in a theater for an excellent performance: Why not?

One simple implication is that the more patriotic you are, the more you ought to believe in a large and growing population. Most of America’s founders certainly had that expectation. Alternately, you might think there is nothing special about American institutions, as many a cynic has argued, and be indifferent about the size of its population. But to arrive at that conclusion, you have to deny there is significant value in the basic American framework.

A growing population also brings practical advantages. Consider the year’s debate over the effect of stimulus on inflation. It doesn’t seem, with a 6.8% inflation rate, that America quite got the balance right. With a significantly growing population, macroeconomic policy is much easier. The growing demands of an increasing number of workers and consumers is itself a form of economic stimulus. But these demands are not in general inflationary, because they are offset by more work and higher output. Those boosts in supply will tend to offset inflationary pressures, and they also will maintain economic growth. A significantly growing population is a kind of macroeconomic free lunch.

More anecdotally, have you ever visited a city and felt a sense of stagnation and decline? For me, that feeling is more common in a city that is losing residents rather than gaining them. There seem to be fewer and less diverse restaurants, theaters, even street musicians.

In contrast, the most exciting states, cities and neighborhoods have lots of new venues and new people. Over the last decade the three fastest growing states, in percentage terms, are Utah, Idaho and Texas. I’ve recently visited the latter two and felt a palpable sense of excitement and ambition.

The relationship between population and dynamism holds at the national level as well, though it is harder to see because declines are not always so concentrated in a single geographic locale. But a country’s mood cannot help but be affected by how many people it has and their ability to make unique contributions to society.

America’s population is not declining right now, but it is not doing much better than holding steady. That brings its own mood of stasis and complacency. And let me be so bold as to suggest that, more than most countries, America is highly dependent on its own sense of optimism and growth. Otherwise, how is it to remain a top innovator? How will it pay off all its debts?

The most common argument against a growing population is that it harms the environment. But any potential solutions to environmental problems involve innovation, and more people means more potential innovators. It is the growing, dynamic societies that are most likely to improve green energy.

Yes, America is in a funk, and low population growth is both a cause and symptom. But this crisis need not be permanent — and one way to solve it is simply to make and bring in more happy people.

Tyler Cowen is a Bloomberg Opinion columnist. He is a professor of economics at George Mason University and writes for the blog Marginal Revolution. His books include “Big Business: A Love Letter to an American Anti-Hero.”

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