As an increasingly crowded world readies to welcome its seven billionth citizen, Japan faces the opposite problem -- a shrinking population that has to depend on a new kind of friend: robots.
While policymakers grapple with questions of how to pay for the burgeoning pension and healthcare costs of a society where the elderly outnumber working taxpayers, engineers say technology could help ease the social pain of ageing.
A variety of companies, ranging from healthcare firms to carmakers, are developing robots they say can provide physical or emotional help to the elderly or those caring for them.
Among the most startling is a bed that transforms into an electric wheelchair from Panasonic, and a robot programmed to gently wash the greying hairs of people who find it difficult to lift their arms.
"Our concept is to provide a total solution for the silver society, not only for Japan but also the world," said Yukio Honda, director of Panasonic's robot development centre.
The Japanese are famously some of the longest-living people on the planet, with the average man reaching 80, while women live to 86. The country also has an eye-popping number of centenarians and regularly holds the record for the world's oldest person.
But a chronically low birth rate means the post-World War II population boom is set to be dramatically reversed.
The nation currently has 127.7 million people, with 23.2 percent of them older than 65.
Figures released this week showed the number of Japanese citizens in the country -- as distinct from foreign residents -- has dropped for the first time since statistics began to be compiled in 1975.
The population is expected to fall to 89 million by 2055, with four out of 10 classed as "elderly", according to the National Institute of Population and Social Security Research.
Analysts say having a smaller population is not in itself a problem, as demonstrated by the economic and diplomatic successes of many European nations with far fewer people than Japan.
But an ageing population causes all manner of difficulties, most notably for Japan's government finances, already hard pressed by two decades of economic stagnation.
More retirees inevitably means more spending on social security when Japan's public debt, at twice GDP, is already one of the industrialised world's worst.
And with public money squeezed, there is little available to help would-be parents with the cost of child-rearing. Added to this the rigid work culture of Japan Inc. and the birth rate is well below replacement.
Japanese women give birth to an average 1.39 children during their lifetime, far below the 2.07 necessary to maintain the current population and well below the 3.65 children of 1950.
Japan is not alone in facing a greying, shrinking population, but it is ahead of the curve, say experts, and will be keenly watched for how it deals with the problem.
"Many countries faces similar problems, but Japan is at the front of the trend," said Hitoshi Suzuki, chief researcher at the Daiwa Institute of Research.
"Should Japan manage to overcome this, it can be a model for other nations to learn from."
Technology firm Cyberdyne is among the Japanese firms looking to capitalise on the "silver yen", developing robotic legs that elderly or injured people can wear for physical therapy to regain muscle mass and help them to walk again.
Already used in hospitals across Japan, they monitor signals from the brain and move the robot's limbs as the wearer tries to move their own legs.
Toyota Motor is trying to develop "partner robots" that will be able to do household chores and help doctors, nurses and caregivers.
On the emotional front, health care firm Pip is preparing to launch "Unazuki Kabochan", a battery-powered doll with audio, light and motion sensors that talks and interacts with its owner to keep them company.
Along similar lines, technology firm Vstone has introduced "Torero", a red panda that gives exercise instructions and words of encouragement to help elderly owners remain active.
The robots might not provide a long-term answer to Japan's population crisis, but the technology they use may have industrial applications, said Suzuki of the Daiwa Institute of Research.
And that might be the key to capitalising on Japan's greying population, with its more sprightly members able to use equipment to work far longer into what would otherwise be their retirement.
"Technological advancement should help improve productivity in the manufacturing and service sectors," he said. "A key issue is how Japan will create a nation where everyone can work if they wish."
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