I keep getting e-mails asking me what I think of John Tamny’s column, saying that advanced nations don’t need to worry about falling birthrates because improved productivity per worker will make up for any potential economic consequences.

Well, the short answer is I don’t think much of it. It struck me as a quaintly retro reprise of old-hat economic reductionism. Apart from anything else, much of a society’s self-image assumes a certain amount of youthful energy: Hollywood movies are full of young people. Sports teams are full of young people. Google gets invented by young people. If you have, as Spain’s heading towards, an inverted family tree of four grandparents with one grandchild, you’re not exactly going to be on the cutting edge of the zeitgeist.

Secondly, even the productivity numbers depend on a bit of old-fashioned clock-punching. Mr Tamny cites approvingly American workers’ position as Number One on the Productivity Hit Parade. But “GDP per worker” is a crude statistic. Frenchmen are as productive as Americans hour for hour, but they don’t put in as many of them: They like 35-hour weeks with a month-and-a-half of paid vacation per year, and they’ve no wish to work like Americans. It’s like two farmhands picking crops in a field: One knocks off at lunch and goes drinking for the rest of the day; the other carries on till five. Mr Tamny would say the latter is twice as productive as the former. But in reality it’s the non-economic factors that drive the numbers.

Heigh-ho. In the end, he falls back on the global economy’s “productive exchange among peoples” -i.e., the west using the Third World as its nursery. We need more doctors and taxi-drivers? Why, here’s a couple now, straight off the boat! But, as everything from the doctors’ plot at Glasgow Airport to the taxi-drivers’ refusal to carry seeing-eye dogs at Minneapolis Airport reminds us, immigrants themselves decline to subscribe to the confines of economic reductionism. Mr Tamny may see a bus driver as a bus driver, but what if the bus driver himself regards his core identity as being something rather different? It shouldn’t be necessary to direct an economic reductionist to, say, Stanley Kurtz’s postings here on Mirpuri cousin-marriage in northern England to make him understand that there are broader and transformative cultural elements that come into play. All over the world from Gaza to Yugoslavia you find people who reject their economic identity in favor of what Mr Tamny would regard as an irrational alternative. The current debate in booming Malaysia about replacing English Common Law with Sharia is only the latest example.

To modify Oscar Wilde, an economic reductionist is a man who knows the price of everything but the value of nothing.