It is a truism that human beings are living longer and longer these days. I suppose most people assume that the sight of elderly people who have difficulty walking is due simply to the effects of old age. At least where I live, it is common to see seniors who can only get around in a wheelchair or with the aid of a cane or some other walking aid. But I suspect there is another reason for this widespread debility.
Human beings who spend long periods of time in outer space, where they are not subject to the constant pull of gravity, are at risk of both muscle and bone deterioration. This is because when these limbs are not subject to the regular stress that results from gravity, they begin to atrophy. Moreover, this deterioration has nothing to do with inadequate nutrition. Astronauts now make sure to exercise regularly while they are in orbit to counteract these losses in muscular and skeletal strength. Comparable muscular and skeletal atrophy is visible in the case of individuals who are hospitalized following a serious injury and, as a result, spend a long time in bed. They must undergo physical therapy in order to strengthen the parts of their body that were not used during their period of inactivity.
From these and other observations, it is clear that the human body distributes nutrients for the growth and repair of muscles and bones to the parts of the body where they are needed. This makes sense since the contrary mechanism – to distribute scarce nutrients to parts of the body that are not used regularly – would make the survival of the organism less likely. Activities like walking, carrying things such as groceries, and doing manual labour stress the body and so help to maintain it in good working order – provided, of course, that they do not cause injury. Parts that are used more regularly than others will receive more nutrients than parts that are used infrequently.
The present generation of old people – people who are now in their sixties, seventies, eighties, and nineties – are among the first generation of human beings that, at least in affluent societies, had access to all kinds of transportation and labour-saving devices such as cars, buses, elevators, and escalators. Many of these individuals were driven from place to place by their parents when they were children, and consequently they developed the habit of driving instead of walking, taking the elevator or escalator when they move from one level to another, and using other mechanical devices that greatly reduced the amount of physical activity they performed. As a result, their bodies were weakened and, not surprisingly, many of them now have difficulty performing basic activities such as walking. This was not a problem when they were young, when their bodies were more resilient; but now that they have become old, it is too late to atone for their past laziness, since the human body’s ability to repair and maintain itself diminishes with age.
The lesson to be learned from their pitiful condition is obvious: good bodily health is not simply a matter of good nutrition – it is also a matter of regular bodily usage. I am not referring to vigorous bodily exercises such as running or lifting weights; I am referring to everyday activities like walking, using the stairs instead of the elevator or escalator, and carrying groceries from the supermarket instead of using a car to transport them from the store to one’s home. If you want to retain the ability to do these things when you are old, then you must get into the habit of doing them when you are young, instead of relying on mechanical means – those silly labour-saving but frequently energy-profligate devices that are created by human ingenuity and are widely used because of human laziness – which many people believe are superior to basic human activities like walking, climbing stairs, and carrying things.
In addition to all the many other problems caused by cars – pollution, urban sprawl, congestion, obesity, the profligate use of limited resources, and accidents that cause the deaths of numerous living organisms, both human and non-human – there is another problem that is becoming increasingly evident as people live longer and longer: if you drive everywhere and frequently use other labour-saving devices, then you are more likely to have difficulty walking and performing other basic activities, which you now take for granted, when you grow old. This is an entirely fitting punishment, since those who depend on cars and other mechanical means to get around when they are young become increasingly dependent on them as they grow older, until they are no longer capable of moving around without them. Ironically, the car, which many people believe provides them with greater physical independence, renders many people less physically independent in their old age, when they are no longer capable of using their legs to get around – the oldest form of locomotion known to humans – because they didn’t bother to use them regularly when they were younger.
 In contrast, other organisms that live in the wild, such as fish, birds, insects, reptiles, amphibians, crustaceans, and our fellow mammals, are living shorter and shorter lives, their lives cut prematurely short by our rapacity, gluttony, selfishness, thoughtlessness, and general indifference to their plight and well-being, as we take over their land, overfish the oceans, seas, lakes, and rivers, and pollute the land, air, and water in which they live.
 While we are on the topic of bone deterioration, the common belief that one must consume milk and other dairy products regularly in order to maintain skeletal health and growth is a misconception that has been encouraged by the dairy industry. After all, there are many large herbivores, such as cows, horses, bison, giraffes, elephants, and rhinoceroses, that do not consume any milk after they are weaned, and yet they are able to grow a very large skeleton solely by consuming plants. In addition, the next time you go to a museum or see a photo of a dinosaur skeleton, remember that its massive skeleton was created by a creature that never consumed a single drop of milk during its life, since dinosaurs, like birds and other reptiles, grew from eggs and therefore were not nursed by their mothers.
 Of course, I am not saying that all elderly people who have difficulty walking must have driven everywhere when they were younger and done little physical exercise, since there are other causes of physical disability besides a lack of regular bodily usage.