Below is an Extract from Garden Earth, about population:
Humans, like any other species that conquers a new habitat, shows an exponential population growth. What is unique for us is that we have been able to radically expand our ability to tame nature and other organisms and direct their production to our stomachs and our bodies. Instead of following a typical S-curve of growth, we have two times restarted population growth. The first time was with the introduction of agriculture, the so called Neolithic or agrarian revolution. Before that, our population grew mainly through expansion into larger and larger areas and into more and more ecological niches. Our role was more or less the same, we lived on the surpluses from other species, which we collected, hunted or fished depending on niche. Population growth was very low, perhaps just 0.001 percent per year (to be compared with 1.8 percent 1990). 12,000 years ago, we were probably less than ten million on the planet, and most likely, the ecological limits for further growth were reached. With the transition to agriculture, many more could be fed from a defined area, but not everywhere, as some parts of the world are not suitable for farming. A period of rapid growth ensued. In ten thousand years, the population grew 250 times. At the time of the industrial revolution, the population had reached the new ecological limits in many places in the world. Not so densely exploited areas were rapidly filling up with settlers from Europe, representing one third of the annual population growth of Europe. Through the deployment of huge amounts of fossil fuel, first coal followed by oil, we got the possibility to, once again, take a giant leap to new levels (Chapman and Reiss 1995, Livi-Bacci 1992).
Forty-three countries, including Japan, Russia, Germany and Italy have populations that are stagnant or even decreasing. A larger group of countries, including China and the USA, has reached the stage where new families will be smaller. When next generation reaches fertile age, population will stabilize. The third group will have doubled its population from now to 2050. This group includes many of the African countries, such as Ethiopia, Congo and Uganda. The predictions of the UN have three alternatives for 2050, 10.8 billion, 9.2 billion or just below 8 billion. Most seem to bet on the middle alternative. That Malthus’ horror scenario of mass starvation has kept its appeal over two hundred years coincides with the start of the demographic transition of England following an unprecedented population explosion. And that pattern has been repeated in country after country, so in the same way as Ireland was the frightening example hundred-fifty years ago, Nigeria or Ethiopia are now. Studies of the demographic transition in the high income countries show a strikingly similar pattern in most countries. First death rates decline rapidly - and it is not primarily the old that live longer but more children that survive. This leads to very big cohorts of youth, reaching 35 percent to 40 percent of the population. When birth rates go down after a while, a big wave of people will reach the stages of young adults, mature adults and old people.
Why is population stabilizing?
It is perhaps a strange question, but it is much more remarkable that the demographic transition has taken place and that populations are not growing, than that there has been a population explosion. After all, we have been taught that the strongest driver of them all is to reproduce, to spread our genes. And why are populations stabilizing now and not hundred years earlier or hundred years later? Why is it not stabilizing in the countries where population is still growing? Is the reason technical, such as contraceptives; economic, such as increased wealth; human, such as improved education of women or is it social, perhaps a result of shift in values? It is interesting to understand what drivers which make individuals change their reproduction. There are actually very few reasons for why a European woman (or her possible partner) today only wants two children, while she wanted four some hundred years ago. It appears to completely contradict the socio-biological ideas that humans only act with the purpose to spread her genes. If that were the case, voluntary birth control would never occur. It is more a process of culture and values. For a long period, it was well known that smoking causes cancer and other diseases. Still it was a long and slow process until this insight led to a changed view on smoking and subsequent regulations. It is interesting that the view on smoking is now changing in all countries, also in countries where smoking is perhaps not a primary health problem (because people don’t live long enough to die from cancer). In the same way it appears that the regulation of populations have little to do with if the country is overpopulated or not. Sweden and the Netherlands stabilized their population more or less at the same time despite that the actual population density is very different, large tracts of Sweden are rather "underpopulated" if there is such a thing. So called soft factors, values and education, seem to play a big role here. At the same time, on a global level, it is hardly a coincidence that populations level off at the same time that we see more and more limits to growth.