What are the 3 factors that induced rapid population growth?

This article comes from a response to a Quora question and sumarises a lot of material from my books on population theory.[1] It raises a number of factors that 'traditional' demographic theory usually cannot investigate due to its very narrow range of inquiry. There are more than three factors mentioned here and they are: Sea-level rise after last glacial maximus pushed populations together and created more fertility opportunities; Changing transport technology created more fertility opportunities; The rise of cities created more fertility opportunities; and the commodification of land and the rise of money created more fertility opportunities; local tribes had immunity to local pathogens so had lower infant mortality and better life expectancy; Inheritance law variations and the creation of land-less labor; The importance of fossil fuel (coal, petroleum) in expanding and supporting bigger populations; to which I could have added, the importance of wood supply as a pre-fossil-fuel limiter of population. I also mention that the theory explored does not conflict with Hamilton's inclusive fitness theory which Dawkins used to develop his 'Selfish Gene' theory, however it does identify countervailing forces to the associated 'Every creature breeds to the maximum' theory.

These examples all come out of Evolutionary Sociologist, Sheila Newman’s book series: Demography Territory Law: The Rules of Animal and Human Populations, Countershock Press, 2013 and Demography Territory Law 2: Land-Tenure and the Rise of Capitalism in Britain. Also a short book by the same author, called, The Urge to Disperse, 2012. I think that all are available at amazon.com and at Lulu.com. Newman also has a big chapter on other population theories in her Rules of Animal and Human populations. Her theories do not conflict with Hamilton’s ‘inclusive fitness’ theory, but they do identify a countervailing force.

1. Hypothesis: Sea-level rise after last glacial maximus pushed populations together

Sea-level rise after last glacial maximus pushed populations together, increasing fertility opportunities for humans who previously had more limited marriage opportunities due to the impact of incest avoidance limiting possible partners within their own clan or tribe. (Degree of incest avoidance depended on how dense a population the local environment could support. For instance, Australian Aborigines who lived in the desert and Koreans who lived in tough mountainous landscapes, practised kinship avoidance to the 8th degree, but other peoples in lush landscapes married their first cousins, as prescribed, for instance in Leviticus. See this article for more: Overpopulation: Endogamy,Exogamy and fertility opportunity theory) (Note also that most other species practise incest avoidance, with varying degrees of endogamy relevant to territorial considerations - see Newman’s Rules….) As rising sea-levels pushed populations together, and humans intermarried within a bigger pool (thus increasing fertility), they had to find ways to get more out of the land than just hunting or gathering would permit. They began to cultivate plants and to herd and fence food animals. This developed into farming. (More conventional demographic theories assume that humans always ‘progress’ and that farming was a better way to live, however this theory is undermined by the negatives associated with farming; less freedom, formation of social castes and lowered height and life-expectancy among the laboring classes.)

Conflicts occurred due to these post-glacial movements and invading or colonising populations sometimes dominated other populations, pushing independent tribes together and enslaving or enserfing them. The colonising populations controlled land-tenure and tended to closely intermarry within their own people (forming a ruling caste or dynasty) to restrict that control to their own kind. The people they had colonised then worked for their colonisers and lived more densely and more poorly than the caste that controlled them. This pattern continued with the rise of agriculture, then with the rise of coal and petroleum technology which helped feed more people and transport armies and immigrants all over the world, transforming traditional functional economies into industrial economies and displacing their populations into cities where more would marry providing cheap and plentiful labor for new industries. Where there were no effective child labor laws families having many children could supplement their otherwise poor income opportunities with children’s wages. (Refer also to Doepke’s theory contrasting modern south Korea with a south American case.)

2. Changing transport technology:

In early times humans traveled on foot like other terrestrial animals, so it was hard to meet a partner outside your immediate community and, because the land your community owned was also limited, there might not be enough land for you to support a family, so you did not marry for that reason. People later learned to use other animals, such as elephants, horses, cattle, as transport and could move further and more quickly than they could on foot. Later or concurrently they learned to build boats and ships, which could take them across rivers, seas and oceans. Then they developed trains and planes and automobiles, which could transport masses of people almost anywhere. With each change in transport technology, humans who were previously mostly limited to one locality, clan and tribe, where they might never marry and have children because there were no unmarried prospects who were not related too closely to them and there were no vacant houses and land available, were now able to find unrelated partners and new homes further and further away. Their fertility opportunities had increased. Consider, for example, how cheap petroleum plus cars coincided with the babyboom and housing in new suburbs.[2]

3. The rise of cities:

The rise of agriculture to service increasingly dense populations resulted in markets, then towns and cities. In the British economy (but not everywhere, not in France, for instance, which also practised contraception and limited family size from 1789 in a pre-industrial ‘demographic revolution’ see English translation of Etienne Van de Walle: “French fertility in the 19th century,” by Sheila Newman) peasants in the country were dispossessed by enclosure movements backed by the ruling classes. Immigrants also came from overseas either seeking work or seeking cheap labor, knowing that it was plentiful in Britain. (A very important 4th factor in population growth were British inheritance laws of primogeniture which only allowed land to be inherited by the firstborn son. All the other children risked becoming ‘land-less labour’ and it was this land-less labor that fueled industrialisation in Britain and British colonies. Some other countries e.g. parts of the Netherlands had similar inheritance laws and early cities, high internal and overseas immigration and new technologies. Some countries increased the supply of labor to industry and cities by ‘freeing’ their serfs but leaving them landless, so that they had to find work in the new industries. (Note also that serfs had often been forbidden to marry anyone but serfs from the same community, which limited their fertility opportunities in necessarily small farming communities. When they went to the cities and found waged labour, they married ex-serfs from other regions who had also moved to the city.) The British industrial revolution spread to many places in the world and the British rewrote the inheritance and land-tenure laws of the countries they colonised, e.g. India, causing explosions of population in Australia, America, Africa, India and Polynesia, for instance. (In order to appreciate different systems, consider that French and Japanese influence on Pacific Islands has not resulted in the same overpopulation on these islands as British, Dutch, and American influence. ) The aforementioned population explosions were multiplied by mass immigration. As mentioned in the first part of this answer, away from one’s own local clan and tribe, cities provided far more marriage/fertility opportunities, especially since the chances of being related to people in the city were much smaller. Where the other limiting factor in local tribes had been lack of new territory, sufficient to provide for a marriage partner and children, the cities provided wages in lieu of land (see rise of money in Newman’s Origins of Capitalism in Britain), and meant that people who would otherwise not have married, did marry and produce children.

A good way to understand how relatively recent our megapopulations are is to consider how Africa and India were able to support huge predators and herbivores. These creatures only became endangered by the recent rise of populations which were probably localised and relatively stable with good survival and life expectancy. You should also question the received wisdom that people all died young and consider instead the principle that local populations inherited immunities to local conditions. (See also Kaplan, H., Gurven, M., Winking, J. 2009, “An Evolutionary Theory of Human Lifespan: Embodied Capital and the Human Adaptive Complex,” for Handbook of Theories of Aging.) Denser farming and city populations were exposed to new diseases and risks and they tended to have very high infant mortality, but those who survived to adulthood might live quite a long time, even into their 80s and 90s. Think of the biblical 3 score and 10 years as a rule handed down and question what you are told about people living longer in modern times. Early agriculture and industrialisation employed people like slaves, in insanitary conditions, and this is still the case in ‘developing’ countries. Petroleum (Another very important factor in population growth, following on from coal) Those countries that controlled petroleum (not necessarily the countries that produced it) have been able to give their populations technological advantages that have decreased infant mortality and increased life expectancy. Conflict over fossil fuel may mean that those dominant first world countries will not be able to maintain these features of life-expectancy for long. Signs of this are increasing internal wealth-gaps in the first world and conflict in the ‘third world’ they have traditionally ‘mined’. Fracking may cause more problems than it solves.

Another very important factor that I allluded to but have not described here, is the commodification of land and the rise of money, the dynamics of which Newman also explores in detail in her second book on Origins of Capitalism in Britain.

NOTES

[1] This article comes from a response under a pen-name to a Quora question and summarises a lot of material from my books on population theory. I usually don't use my own name or give personal details on major public internet platforms, due to privacy and hacking concerns. Having gone to the trouble to describe parts of my theory on Quora, I have decided to re-use the material here.

[2] I forgot to mention the babyboomers as an example of the impact of new transport (and fuel) on fertility opportunity in the original pen-named article.