The simple population studies in the evolution section employed creatures which generally reproduced at a constant rate in a field or pool of nutrients. These populations tended to grow exponentially until the nutrient pool became depeleted, idleness fell, and the creatures died en masse, the few survivors repeating the process thereafter.

If the same logic were to apply to human populations, much the same could be expected to happen. Humans would multiply exponentially in numbers until a population crash cut numbers back.

But there are several reasons for supposing that this is unlikely to happen. In the first place, humans can increase the size of their 'nutrient pool' by increasing farmland. And they can boost crop yields by the use of fertilizers, weedkillers, insecticides, and also through the cultivation - perhaps using genetic engineering - of high yield crops. In this manner, as human numbers rise, more and more farmland comes into use.

Of itself, this would only support exponentially rising human numbers to the point where the entire surface of the earth was farmland. But it's not the case that humans reproduce at a constant rate. Humans can and do exercise choice over their reproduction. Contraception, delayed marriage, and a variety of other factors may affect reproduction rates.

The influence of idleness on reproduction

Economic growth, in Idle Theory, is essentially growth in human social idleness. In modern Western society, rising social idleness largely appears not so much as rising disposable free time, but rising material prosperity while everyone keeps working. Rising idleness has brought modern consumer society.

Economic growth is largely driven by science and technology, which is cumulative in nature, as new skills and techniques and tool systems are passed on to subsequent generations. The cumulative nature of this technological growth results in slowly but steadily rising idleness, even if some resources (e.g. timber) become depleted. Human history is thus one of slowly rising idleness.

Busy, low idleness human society is labour-intensive. Life is one long round of unremitting toil. And in these circumstance human lifetimes must tend to be relatively short, because there is a high likelihood that humans will suffer injuries - broken bones and the like - from which they never recover. In part they may not recover because other people may be too busy to care for them while they recover. Equally, in low idleness societies, where a lot of work is required to provide food and water and shelter, these may often be in short supply, resulting in famines, droughts, and exposure to extreme heat or cold, with further consequent mortality. And, for all the same reasons, the care of human infants is likely to be minimal: parents may even sometimes face the stark choice of feeding themselves or their offspring, and choosing the former. The net result is that in low idleness human societies, human numbers will rise very slowly. Many children will die in infancy, and those who survive into adulthood may be killed by accident, disease, famine, drought, exposure, or any number of other causes.

By contrast, as human idleness rises, and less work needs to be done to provide the necessities of life, improved care of infants, of the sick and injured, and finally the elderly (if there are any) becomes possible. With food and water relatively easy to come by, diets improve, and famine and drought pose less of a threat. And finally, simply because humans work less, they suffer less injury, and less wear and tear (in the form of arthritis, for example), and tend to live longer. More infants survive into adulthood, and more adult survive into old age. And the result of this is that human populations tend to rise relatively rapidly.

Busy, low idleness human societies are also necessarily labour intensive. In fact, in many cases, human beings may be the only all-purpose tool - doing all carrying, cutting, gathering, almost unaided by any tools -. In this circumstance, particularly given high mortality rates, human reproduction provides a steady supply of useful human tools. Infants will be set to work as soon as they can walk and talk. The labour that they save their parents will, as with all useful tools, exceed the cost of their production and maintenance. Children will be an economic asset, and in many cases the prime asset in human society. The role of women in such busy societies is likely to be that primarily of child bearers and carers, with many of their children dying in infancy. The role of women will be to produce as many children as possible, preferably strong sons.

When human idleness begins to rise, and care of infants improves, women who are maximally reproducing, perhaps having 10 or 20 children, before themselves dying in childbirth, will find that instead only 2 or 3 of their offspring reaching adulthood, 7 or 8 will get there. Families will grow in size, and human numbers will multiply.

And while a first child will generally be of primary value to its parents, and second and third child will generally be of less value, assuming there is only so much work that needs to be done. Beyond some point, further children may become a liability than an asset. Mothers may welcome their first child with joy, but not their 20th child. And as human numbers grow, they will tend to outstrip the resources locally available to them, necessitating relocation to new lands, new farms, new hunting grounds. Rising human populations must bring rising human mobility. And with rising mobility, collision and conflict with other human societies.

If economic growth continues, and human idleness continues to rise, then in relatively idle societies, in which little work needs to be done, children will be less and less of an asset. They will cease to be useful tools, to be set to work as soon as they are able. They may require training or education before they can be usefully employed. And the result of this is that children in the highest idleness societies will be almost entirely luxuries - whose costs exceed their value. In the highest idleness societies, people will increasingly tend - using contraception or late marriage - to have only one or two children, and in many cases none at all. And should human reproduction fall below replacement levels, human populations will fall.

The net result of all this will be that human populations will tend to remain low at low idleness, and begin to rise more and more rapidly as idleness rises, and then slow and begin to fall, and continue to slowly fall thereafter.

So the long term human population graph is likely to see a rise to a peak, before falling away.

If exponential population growth continues, there is a high population peak followed by a crash. And when exponential population decay sets in, humans may even dwindle out of existence.

Before the population peak, human populations will be generally young, with relatively more children than adults. After the population peak there will be ageing populations, with relatively more adults than children. During the population decline, cities that expanded during the population boom will contract, farmlands will fall out of use, forests will regrow, birds and fish and all living things will multiply.

At the very highest levels of idleness, in which mothers are largely relieved of the task of caring for infants, children will perhaps begin to seem to seem neither as useful assets nor as burdensome luxuries. Humans may be entirely indifferent to whether human populations rise or fall. And if, as a consequence, no care is taken to use contraception or late marriage or any other device to minimize reproduction, human numbers may then start to grow again.

Current fears

Given that humanity is currently in the middle of a population boom unprecedented in human history, it is not very surprising if the prevailing nightmare is one of exponential population growth, resource depletion, followed by population crash. It seems to a great many people that the planet is now overpopulated by humans. And, of course, relative to its prior levels it is relatively overpopulated, and set to become even more highly populated.

But already the economically most advanced countries have completed their population growth, and now have declining populations. Food production has kept pace with population growth, and the standard of living in the less developed countries is rising rapidly, suggesting that soon their populations will begin to start to decline.

Since population decay has set in in Europe, Russia, and America, while populations are still rising in India and Pakistan and China and other far eastern countries, there is likely to be high rates of population flow from the less developed growing areas to the more developed dwindling areas. America and Europe will continue to see high rates of immigration. And where population pressures are not relieved by such movements, there is a possibility of wars in which expanding populations in China or India or elsewhere move en masse into neighbouring relatively underpopulated areas. Such migrations and wars will end once the population peak has been reached.