As the last quarter of the year gets underway, all eyes are turning to the population clock maintained by the Census Bureau. It stood somewhere north of 299,878,864 by yesterday evening, and America’s census odometer is expected to roll over to 300 million between now and the end of the year. It’s a reminder of how quickly the country has been growing of late. It took until 1915 for America to reach the 100 million mark and another 52 years before the population hit 200 million. It has taken only 39 years for the country to accumulate another 100 million souls.

The thing to remember as the population clock spins is that American is an under-populated country. We need vastly more people than we currently have to maximize our political, economic, and cultural potential — we would even say to achieve our national destiny. No doubt there are some fussbudgets who will pipe up and ask, what is the number at which America would not be under-populated? We don’t see where that question needs to be answered to grasp the vast amount of room America currently has to grow and to comprehend — which one can do by looking at, say, Europe — the tragedy of population declines.

America’s population growth has been among its greatest strengths. It has been due to both natural population trends and to the beneficence of modernity. American fertility rates in the middle of the 20th century were well above the replacement rate — the number of children the average family must have in order for the children’s generation to fully replace the parents’ — and while the fertility rate has since declined to barely the replacement rate, the earlier baby boom will echo for generations to come. Improved medical care and the cornucopia of modern agriculture are prolonging life spans, allowing more women and children to survive childbirth and letting more people reach ever older ages, increasing the total number of people alive at any one moment.

Immigration has been helping us grow, as well, a point we have kept in mind reading the debate in our pages between two of the keenest writers on the subject, Diana Furchgott-Roth and Steve Malanga. As of 2004, the Census Bureau estimated that 34.3 million foreign-born individuals were living in America, a number that doesn’t include illegal immigrants currently estimated at between 11 million and 12 million. Immigrants are a demographic gift that keeps on giving. Not only do they augment today’s population numbers, but they also increase tomorrow’s count because in general they, and especially the Hispanic immigrants among them, have significantly higher total fertility rates than native-born women.

No one doubts that for all the benefits immigrants bring, their arrival creates economic and social pressures, dividing even those who are generally on the same ideological side on so many other issues. Mr. Malanga, who is with the Manhattan Institute, has written in City Journal that the current wave of immigrants is overwhelming low-skilled workers, social welfare programs, and society at large. Ms. Furchtgott-Roth, who is with the Hudson Institute, counters that the anecdotes aren’t supported by hard data.

Mr. Malanga and others on his side argue that this wave of immigrants is different from earlier ones. The Irish, Italians, and Eastern Europeans didn’t find themselves enfolded by a massive welfare state.Before the advent of “multiculturalism,” those immigrants found themselves under more pressure than today’s newcomers to assimilate and become fully “American.” Better schools made it easier for them to equip their children for success, as did a proliferation of lowskilled but high-paying manufacturing jobs. Ms. Furchtgott-Roth summons statistics to suggest that the disadvantages today’s immigrants face by comparison have been overstated.

While we have great regard for the participants in this debate, we’d rather have the people than not have the problems. We favor public policies that provide a hospitable environment for population growth and large families.We cast no value judgments on those who live single lives or who are childless. But we do reject the warnings of Malthus and his ilk.They have been proven wrong in each generation. In the decades since the book “Too Many Asians” predicted famine in Asia, its population soared and hunger collapsed save in a few places like Communist North Korea. By our lights, the missing element to the population debate is the teachings of the religious sages, which enjoin us to choose life and multiply. The sages never said stop at 300 million, and we look forward to reaching the next 100 million sooner rather than later.