A Brief History of the World Population
by Massimo Levy-Baci
Translated by Wang Shuai Shu Tian Bi Tianyu
China Friendship Publishing Company
How did humanity rise and fall from 1 million in the Paleolithic age to 7 billion today? Why is the world's population 7 billion, not more nor less? Some people think that the earth can accommodate 10 times more people than it is today, is there really so many resources for human consumption?
In fact, the worldwide fertility boom has passed. The global average fertility rate is declining. However, the demographic problems faced by countries around the world are different: many developed countries face a demographic crisis, ageing and declining birthrates, while many African countries face excessive population growth and a worsening living environment. So, what will the future trend of the world's population look like? How is population and resources balanced? Is population growth a pressure or a driver?
This book looks at human history, from primitive societies to the population explosion after the Industrial Revolution. In the book, we can see the mechanism of world population change and the difficult process of population migration, understand the cyclical laws of population growth, stagnation and decline, examine how the balance between population and resources and the environment is maintained, and the ultimate impact of population on history, geography, countries and the overall destiny of mankind.
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Number of future populations
As I have already mentioned, today's population is characterized by strong momentum, so population projections for the coming decades are quite reasonable. For example, by 2035, the population aged 20+ will be the generations born before 2015, which means that these people have been born and counted. It is only necessary to subtract the mortality rate on this basis, and the mortality rate is quite stable. But the size of the population born between 2015 and 2035 is unknown, depending on two variables. The first variable is the size of the population of childbearing age, which is no secret that people who enter the reproductive period in the next 20 years will already be born. The second unknown variable is the fertility intention of this part of the population, at which point we can only guess. In the long run, even if predictions are based on complex aesthetically attractive methodologies, predictions become increasingly uncertain, and predictions can only illustrate what is possible in the future, rather than an exploration of reality in the future. Without considering this much here, I will only give an example of the population projections by the end of the 21st century, which are almost the next three generations. These projections are based on assumptions about the reproductive behavior of unborn women (and men), as well as assumptions about the fertility behavior of their children and their children's children, who will make their own decisions in the next 30, 60 or 90 years of social circumstances.
In a relatively short period of time, say, in decades from now, the enormous inertia of demographic change will make population projections easy. There are several ways we can measure population inertia (or momentum). One way to do this is to imagine people adopting replacement fertility rates from today, rather than abandoning replacement fertility rates, which will eventually lead to a stable population (zero growth) while keeping the mortality rate fixed and net migration zero. But if the population in question has only recently had high fertility rates and therefore has a young age structure (as in many developing countries), it will continue to grow for a certain period of time. In the coming decades, many recently born children will enter childbearing age, and even though each of them has very few children, they will still have a large number of babies due to their large numbers. The number of newborns will far outnumber the number of deaths, since the latter will come mainly from the elderly, who belong to the generations that were born decades ago, when the population was far smaller than it is today. As people born under the new birth system reach childbearing age, the number of births will gradually decline until it is in line with the number of deaths. For example, according to the United Nations projections (Median Variable, 2015 Revision), the population of poor countries is expected to increase from 6.1 billion to 8.4 billion between 2015 and 2050. Even at alternate fertility levels, the population in poor countries will grow to 7.9 billion by 2050. The growth of this 1.8 billion population, instead of the expected 2.3 billion, is the result of the current young age structure or current inertia.
The United Nations has made accurate projections of the evolution of the world's population over a period of time and revised them periodically. Tables 6–1 include the results of major retrospective projections and so-called median variable projections up to 2100. The latter, based on the evolution of fertility and mortality, is considered to be the most reasonable, i.e. fertility in less developed countries will continue to decline, from 2.65 children per woman in 2010-2015 to 2.15 in 2045-2050, with average life expectancy increasing from 69 to 75 years over the same period;
The most interesting results of this prediction are as follows:
The world's population will reach 8 billion in 2023 and 9 billion in 2037.
2. The world population growth rate was 1.1% between 2010 and 2015 and will gradually decline to 0.4% by 2045-2050.
3. However, this rate of decline is based on a very large population, so population growth gradually declined from 84 million between 2010 and 2015 to 54 million in 2045-2050.
The target population for 2050 is 9.7 billion, depending on the expected decline in fertility, which should fall worldwide from an estimated total fertility estimate of 2.51 in 2010-2015 to an estimated estimate of 2.25 for 2045-2050. By the end of this period, the target of total fertility above or below 2.25 would mean an increase or decrease of about 220 million inhabitants by 2050.
5. Between 2010 and 2050, almost all of the world's population growth came from developing countries.
6. Geographical demographic changes will be enormous: between 2015 and 2050, the share of developed countries in the world's population will fall from 17% to 13.2%, while the share of the European population will fall from 10% to 7.3% at a faster rate. Population growth in poor continents will be uneven, with Africa's share of the population increasing from 16.1 per cent to 25.5 per cent.
7. The United Nations boldly predicts the demographic situation at the end of the 21st century. The world's population will reach the 10 billion mark in 2056, 11 billion in 2088, and 11.2 billion in 2100, when growth rates will remain almost stable and close to zero. In 2100, 4 out of 10 inhabitants of the world lived in Africa, 2.5 times the current proportion.
The dramatic increases and changes in population since the 1950s and projections of population in the coming decades will significantly change the ranking of the world's most populous countries (Table 6–2). In 1950, there were 4 European countries in the top 10 countries in terms of population, as well as 2 developed countries in the United States and Japan. Of these countries, only the United States remains in the top 10 by 2050, suggesting that the West will decline in the world's "geopolo demography." None of the African countries made the top 10 in 1950, but the top 10 countries with the most populous populations in 2050 included Nigeria, the Democratic Republic of the Congo and Ethiopia. Pakistan was only ranked 13th in 1950, and it will be 6th in 2050. In 2050, India will replace China as the world's most populous country.
Developments vary across the world, so the ratio of numbers between traditionally conflicted or interconnected populations will change. Although relations between States are largely influenced by political, cultural and economic factors, the relative size of populations between countries is bound to have an impact if there is a major change. For example, the Rio Grande isolates the rich world of North America from the poor world of Mexico and Central America. The population ratio of these two regions was 4.6:1 in 1950 and 2.1:1 in 2050. It is hard to imagine that such a major change in population would not alter relations between countries. In 1950, the population of the northern Mediterranean coast was 2.1 times larger than that of the poor countries on the southern and eastern coasts. By 2050, the ratio will be 0.4:1. Such a reversal is bound to have certain consequences. Indeed, the ongoing upheaval is also the result of demographic transition. What are the countries that have traditionally been in competition or conflict and whose populations are growing at different rates? Turkey and Greece, Brazil and Argentina, Israel and nearby Arab countries (or Arab populations within their borders), as well as China and India.
Predicting future populations means assuming fertility, survival, and migration over the next few decades. The main assumption used by the United Nations in forecasting population is that there will be "convergence" of behaviour between different countries: where fertility rates are too high, they will rise where fertility rates are too low; survival rates will improve everywhere, but in places where life expectancy is high, the pace of survival rate improvement will be slower, and where life expectancy is low, the pace of survival rate improvement will be faster; and the proportion of migrants in both immigrant-sending and receiving countries will gradually decline. With the right technology, demographic change between 2010 and 2050 can be broken down into four components: fertility, mortality, proportion of immigrants, and initial age structure. If the mortality rate remains at the 2010 level and the net migration is equal to zero, the population in 2050 can be calculated, resulting in the contribution of the fertility rate. The contribution of mortality (fertility remains at 2010 levels and migration is zero) is calculated in a similar way. Finally, to calculate the contribution of the initial (2010) age structure (also known as the "inertia" or "momentum" of the population), the fertility level for 2010-2050 is set to the replacement level, and it is assumed that the mortality rate remains fixed at the 2010 level throughout the period, with zero net migration. Quantifying the role of the factors driving future demographic trends helps us to develop policies and programmes that balance demographic change with social, economic and environmental objectives.
Tables 6–3 describe the role of these factors, including the more developed and less developed regions, as well as six populous countries, Japan, Nigeria, China, India, Brazil, and the United States. From 2010 to 2050, the global population will grow by 40%, with most of this growth (+26%) attributable to demographic inertia or the current structure of the young population; fertility rates (+8%) and mortality rates (+6%) will also play a role, while the impact of migration is zero. In Nigeria, for example, with an overall population growth rate of 151 per cent, the largest contribution to future population growth is fertility (+107 per cent), followed by inertia (+39 per cent), while mortality (decline) contributes +7 per cent to population growth, with immigrants only slightly offsetting the growth rate (-2 per cent). Clearly, policies aimed at slowing rapid population growth must focus on controlling fertility rates. On the other hand, Japan will reduce its population by 20 million between 2010 and 2050, with a population decline of 16%, of which inertia (aging demographics) will cause a 11% reduction in population, low fertility will reduce the population by 12%, and further declines in mortality (+5%) and immigration (+2%) will offset part of the population decline. Policy is powerless against an aging demographic, and Japan's death rate is already the lowest in the world. However, if the decline in population is to be limited, Japan can develop policies that seek to increase fertility and the number of immigrants.
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Massimo? Massimo Livi-Bacci: Professor of Demography at the University of Florence, Italy, and former President of the International Union for Population Science Research. Long-term research on contemporary demography and population history, focusing on population development and predicting population trends in countries around the world. He has taught at Princeton University, the University of California, Berkeley, the Institut de France and many other world-renowned universities, and has authored many books and influential papers in the field of demography. He also proposed the concept of "mortality crisis", which was widely accepted by the academic community. Massimo? Professor Levy-Bacci was also elected to the Italian Senate twice.
Author: Massimo? Levy Budge
Edit: Jin Jiuchao