When Gill Pratt sat down to discuss the job of running the Toyota Research Institute, the carmaker's new research division, his Japanese interviewers wrote one word on a piece of paper and asked him to talk about it. The word was dementia.

That might seem a strange topic to put to one of the most respected figures in the world of robotics, a man who had previously run a competition to find artificially intelligent, semi-autonomous robots for the Pentagon. But, Pratt said, the company's interest in aging was a big reason for him to take the job. "The question for all of us," he said, "is, how can we use technology to make the quality of life better as people get older?"

Aging and robots are more closely related than you might think. Young countries with many children have few robots. Aging nations have lots. The countries with the largest number of robots per industrial worker include South Korea, Singapore, Germany and Japan, which have some of the oldest workforces in the world.

The connection does not merely reflect the fact that young countries tend to be poor and cannot afford fancy machines, which they do not need anyway. It holds good within rich countries, too. Those with relatively few robots compared with the size of their workforce include Britain and France, both of which (by rich-country standards) are aging slowly.

Robots typically substitute for labor. That is why many people fear that they will destroy jobs. Countries with plenty of young workers do not need labor substitutes. Wages there also tend to be low, making automation unprofitable. But aging creates demand for automation in two ways.

First, to prevent output falling as more people retire, machines are necessary to substitute for those who have left the workforce or to enable aging workers to continue to do physical labor. Second, once people have retired they create markets for new kinds of automation, including robots that help with the medical and other requirements of caring for people who can no longer look after themselves.

Automation is destiny

As a result, the connection between robots and aging is a powerful one. Daron Acemoglu, an economist at the Massachusetts Institute of Technology, reckons that aging is the biggest single influence upon how many robots a country has. He estimates it explains close to 40 percent of the variation in the numbers of robots countries introduce.

The influence will grow. This year, there will be more people older than 65 than younger than five for the first time in human history. By 2060, the number of Americans older than 65 will double, to 98 million, while in Japan, 40 percent of the population will be 65 or older. There will not be enough younger people to look after so many, unless robots help (and probably an influx of migrants is permitted, too).

Shrinking and aging workforces matter as much. Over the next few years, demography will change the kinds of robots people need, as well as increase the number in use. At the moment, the robotics market is dominated by industrial machines, the sort used to assemble cars or electrical equipment.

As demographic change speeds up, service robots will become more important. One day, their makers hope, they will enable old people to live alone and stay mobile for longer. Robots will help assuage loneliness and mitigate the effects of dementia.

You can see the stirrings of this robot revolution most clearly in Japan. Aibo, a robotic puppy with artificial intelligence made by Sony, and Paro, a furry seal made by Japan's National Institute of Advanced Industrial Science and Technology, are therapeutic robots for children and patients with dementia.

Pepper, made by SoftBank, is a humanoid robot which can carry out conversations on a limited range of topics, so long as its human interlocutor does not stray too far from the script. MySpoon is a robot for those who cannot feed themselves. Hal, by Cyberdyne and Muscle Suit, by Innophys, are exoskeletons, helping nurses pick up and carry patients (Hal stands for hybrid-assistive limb). Panasonics' Resyone is a robotic bed that transforms itself into a wheelchair. And so on.

Demand for these gizmos is growing fast, if from a low base. Sony said it had sold 11,111 Aibos in the three months after the new model went on sale in January 2018. Japan's government reckons that 8 percent of nursing homes now have lifting robots, and its national robot strategy (every country should have one) calls for four-fifths of the elderly receiving care to have some care provided by a robot by 2020.

The number will doubtless grow. The question is how quickly. Pratt is optimistic. Within a decade, he reckons, domestic robots will help people cook at home and car-guidance systems will keep them mobile for longer.

Machine learning

But for that to happen, robots will have to perform a dauntingly long list of things they cannot yet do. They cannot navigate reliably around an ordinary home, move their hands with human dexterity, or conduct open-ended conversations. Although they can provide some physical assistance to the elderly, one robot can do only one thing, so multiple tasks would require your home to be stuffed with machines.

Their limitations have significant implications. Robots that make the end of life more bearable are likely to remain expensive for many years, so only rich people will buy them. That may limit their wider social acceptance. Companies may not be able to automate their way out of future skills shortages.

Other responses, such as raising wages, attracting more women into paid work and allowing more migration, will be just as important. Last, there may be room for the expansion of global-supply chains, as work shifts from aging China and other middle-income countries, to Africa and poorer places with more labor.

Aging demands a robotics revolution, but it may be slow to arrive.