In the roughly 250 years since the Industrial Revolution, the world’s population, like its wealth, has exploded. Before the end of this century, however, the number of people on the planet could shrink for the first time since the Black Death. The root cause is not an increase in deaths, but a drop in births. Across much of the world the fertility rate, the average number of births per woman, is collapsing. Although the trend may be familiar, its extent and its consequences are not. Even as artificial intelligence (AI) leads to optimism in some quarters, the baby bust (婴儿荒) hangs over the future of the world economy.

Whatever some environmentalists say, a shrinking population creates problems. The world is not close to full and the economic difficulties resulting from fewer young people are many. The obvious one is that it is getting harder to support the world’s pensioners. Retired folk draw on the output of the working-aged, either through the state, which requests taxes on workers to pay public pensions, or by cashing in savings to buy goods and services or because relatives provide care unpaid. But whereas the rich world currently has around three people between 20 and 64 years old for everyone over 65, by 2050 it will have less than two. The implications are higher taxes, later retirements, lower real returns for savers and, possibly, government budget crises.

Low proportion of workers to pensioners are only one problem resulting from collapsing fertility. Younger people have more of what psychologists call “fluid intelligence”, the ability to think creatively so as to solve problems in entirely new ways. This youthful energy adds to the accumulated knowledge of older workers. It also brings change. Patents filed by the youngest inventors are much more likely to cover breakthrough innovations. Older countries and their young people are less enterprising and less comfortable taking risks. Because the old benefit less than the young when economies grow, they have proved less keen on pro-growth policies, especially housebuilding. Creative destruction is likely to be rarer in ageing societies, restricting productivity growth in ways that compound into an enormous missed opportunity.

Eventually, therefore, the world will have to make do with fewer youngsters—and perhaps with a shrinking population. With that in mind, recent advances in AI could not have come at a better time. A productive AI economy might find it easy to support a greater number of retired people. Eventually AI may be able to generate ideas by itself, reducing the need for human intelligence. Combined with robotics, AI may also make caring for the elderly less labour-intensive. Such innovations will certainly be in high demand.

If technology does allow humanity to overcome the baby bust, it will fit the historical pattern. Unexpected productivity advances meant that demographic time-bombs (人口定时炸弹) failed to explode. Fewer babies mean less human genius. But that might be a problem human genius can fix.

In the UK, there is one car for every 5 people. In the USA there is one for every 2.5 people. So Americans sometimes have one car for every member of the family.

The family, with whom Liz, a student from Britain, is staying, have got four cars: a Mercedes-Benz for father, who drives it to work, a Chevrolet for mother, who uses it for shopping and visiting her friends, and Alex and his sister both have Fords. All the four cars are less than two years old, but none of them are as large as Liz has imagined.

“Smaller Cars have been made for a long time now,” Alex explained.“Partly because large cars burn up too much gas, and partly because of competition from smaller foreign cars, mostly Japanese and German.”

“I’ve noticed,” Liz said, “that your sidewalks don’t go as far as the suburbs, and yet you’re not supposed to walk along the highway.”

“That’s because nobody walks to work here,” Alex explained. “We do as little walking downtown as possible. We can’t do without our cars. We can do almost everything by using cars.”

“Did your father give you and June your cars?”

“Sure! But he won’t have money for gas or repairs or license. That’s why we both have part-time jobs three times a week. June waits table. I’m a teaboy.”

“But June’s just 17. At home we can’t get a learner’s license till we’re 17.” “We get one at 16 here. So all we have to do is to take a road test and get a driver ‘s license the moment we’re 17.”

Years ago, when I started looking for my first job, wise advisers told me, “Barbara, be enthusiastic! Enthusiasm will take you further than any amount of experience.”

How right they were! Enthusiastic people can turn a boring drive into an adventure, extra work into opportunity and strangers into friends.

It took years and years for the early work of Barbara Mclintock, a geneticist who won the 1983 Nobel Prize in medicine, to be generally accepted. Yet she didn’t stop working on her experiments.【小题2】

We are all born with wide-eyed, enthusiastic wonder and it is this childlike wonder that gives enthusiastic people such a youthful air, whatever their age.

At 90, cellist Pablo Casals would start his day by playing Bach. As the music flowed through his fingers, his stooped shoulders would straighten and joy would reappear in his eyes.【小题3】As author and poet Samuel Ullman once wrote,“Years wrinkle(起皱纹) the skin, but to give up enthusiasm wrinkles the soul.”

How do you rediscover the enthusiasm of your childhood? The answer, I believe, lies in the word itself. “Enthusiasm” comes from the Greek and means “God within”. And what is God within is but a sense of love---proper love of self(self-acceptance) and, from that, love of others.

【小题4】If we can’t do what we love as a full-time career, we can as a hobby. Elizabeth Layton of Wellsville, Kan, was 68 before she began to draw. This activity ended periods of depression that had troubled her for at least 30years, and the quality of her work led one critic to say, “ I am tempted to call Layton as a genius.”

We can’t afford to waste tears on “might-have-been”. We need to turn the tears into sweat as we go after “what-can-be”.

We need to live each moment wholeheartedly, with all our senses---finding pleasure in the backyard garden, the simple picture of a six-year-old, the charming beauty of a rainbow.