Urban Cruise Ship Home

Back to Habitat / Well-Being.


In this section, we review population and fertility trends, factors that govern fertility, and the consequences of population trend.

Population Outlook

Today's world population is approximately 7.7 billion people and growing to a projected 9.6-10.9 billion in 2100 [31]. Uncertainty in the distant future depends on how fertility trends evolve.

Recent trends suggest, however, that the UN may be underestimating future population growth in Africa [10].

Unforeseen social trends could significantly alter population forecasts [2]. The advent of life extension [9] and advancement in assistive reproductive technology such as in vitro fertilization [5] might modestly increase forecasts in the 21st century. It is also unclear the extent to which the current low fertility regime will induce natural selection pressures toward large families, causing an eventual rebound [2].

Fertility Trends

The main variable governing long-term population trends is the total fertility rate: the number of children born to women on average. TFR tends to be higher in lower income countries. Sustained over a long time, a TFR above about 2.1 and no net immigration means that a country's population will grow, and a TFR below 2.1 means that population will shrink [33].

Total fertility rate by select regions and countries. Source: World Bank [29].

Since 1964, world TFR has been decreasing.

World total fertility rate from 1960 to 2018. Source: World Bank [29].

Determinants of Fertility

Broadly speaking, there are three classes of explanations for falling fertility. The cultural evolution hypothesis that modernity tends to spread norms that encourage fewer births [4][22]. The quality/quantity tradeoff holds that, as children's educational needs grow, parents make a rational decision to have few children while improving the education (quality) of those they do have [7]. Modernity may reduce the impulse to have children by allowing the pursuit of competing desires, such as noncommittal romance or women's career fulfillment [34].

The following correlates with fertility rates have been observed.

Select factors that correlated with fertility and observed effects. Note that many studies establish correlation but not necessarily causation. Note also that, insofar as the factors are policy-relevant, there are many considerations other than the effect on birth rates to consider, and Urban Cruise Ship does not endorse particular policies. Sources: Bauernschuster et al. [1], Herzer [12], Kulu et al. [15], Kulu and Washbrook [16], Lerch [18], Levine et al. [19], Madsen and Strulik [21], Shoag and Russell [25], Stone [27], Stover and Winfrey [28].

It is debated how many births were prevented by China's One-Child Policy, the most notable coercive population control policy in history, though the policy is responsible for severe human rights abuses and long term social damage [6].

Consequences of Demographic Trends

Economists generally argue that, in industrialized countries but not necessarily in poorer countries, a higher population should lead to higher per capita economic growth due to there being more researchers, more opportunity for specialization, and economies of scale [8][13][14][23][26][32], though see Coleman and Rowthorn [3] for an alternate view.

If coupled with investments in human capital, especially education, a transition from a high birth and death rate to a lower birth and death rate can free up resources from childcare and catalyze rapid economic development [20]. Following a protracted period of low birth rates, countries experience an increase in the share of the retired population, which depresses growth [17].

Our analysis of the role of population growth in human environmental impacts is in progress.

Philosophical Considerations

One's views on population policy may be influenced by choice of ethical framework. Among utilitarian frameworks, an average utility model, as articulated by Hardin [11], holds that the average well-being among people is the morally relevant quantity. The total utility model holds the sum of well-being over all people to be the morally relevant quantity [30]. A total utility view would generally be more pronatalist than an average utility view.

Relatedly, there is the question of how ethically to value a hypothetical future life brought into existence, relative to lives that already or will exist [24].

Philosophers do not have a concensus on the best way to resolve these issues.

Back to Habitat / Well-Being.


[1] Bauernschuster, S., Hener, T., Rainer, H. "Does the Expansion of Public Child Care Increase Birth Rates? Evidence from a Low-Fertility Country". Annual Conference 2013 (Duesseldorf): Competition Policy and Regulation in a Global Economic Order 79909, Verein für Socialpolitik / German Economic Association. 2013.

[2] Burger, O., DeLong, J. "What if fertility decline is not permanent? The need for an evolutionarily informed approach to understanding low fertility". Philosophical Transactions of the Royal Society B 371(1692): 20150157. April 2016.

[3] Coleman, D., Rowthorn, R. "Who’s Afraid of Population Decline? A Critical Examination of Its Consequences". Demographic Transition and Its Consequences 37, pp. 217-248. 2011.

[4] Colleran, H. "The cultural evolution of fertility decline". Philosophical Transactions of the Royal Society B 371:20150152. April 2016.

[5] Faddy, M., Gosden, M., Gosden, R. "A demographic projection of the contribution of assisted reproductive technologies to world population growth". Reproductive Biomedicine Online 36(4), pp. 455-458. April 2018.

[6] Feng, W., Gu, B., Cai, Y. "The End of China’s One-Child Policy". Studies in Family Planning 47(1), pp. 83-86. March 2016.

[7] Galor, O. "The demographic transition: causes and consequences". Cliometrica 6, pp. 1-28. 2012.

[8] Garza-Rodriguez, J., Andrade-Velasco, C., Martinez-Silva, K., Renteria-Rodriguez, F., Vallejo-Castillo, P. "The relationship between population growth and economic growth in Mexico". Economics Bulletin, AccessEcon, 36(1), pp. 97-107. 2016.

[9] Gavrilov, L., Gavrilova, N. "Demographic Consequences of Defeating Aging". Rejuvenation Research 13(2-3), pp. 329-334. April 2010.

[10] Gerland, P. et al. "World population stabilization unlikely this century". Science 10 Vol. 346 no. 6206 pp. 234-237. October 2014.

[11] Hardin, G. "The Tragedy of the Commons". Science 162(3859), pp. 1243-1248. December 1968.

[12] Herzer, D. "A Note on the Effect of Religiosity on Fertility". Demography 56, pp. 991-998. April 2019.

[13] Jones, C. "The End of Economic Growth? Unintended Consequences of a Declining Population". National Bureau of Economic Research, NBER Working Paper No. 26651. January 2020.

[14] Kremer, M. "Population Growth and Technological Change: One Million B.C. to 1990". The Quarterly Journal of Economics 108(3), pp. 681-716. August 1993.

[15] Kulu, H., Boyle, P., Andersson, G. "High suburban fertility: Evidence from four Northern European countries". Demographic Research 21(31), pp. 915-944. December 2009.

[16] Kulu, H., Washbrook, E. "Residential context, migration and fertility in a modern urban society". Advances in Life Course Research 21, pp. 168-182. September 2014.

[17] Lee, H., Shin, K. "Nonlinear effects of population aging on economic growth". Japan and the World Economy 51: 100963. September 2019.

[18] Lerch, M. "Fertility Decline in Urban and Rural Areas of Developing Countries". Population and Development Review 45(2), pp. 1-20. December 2018.

[19] Levine, P. B., Staiger, D., Kane, T. J., Zimmerman, D. J. "Roe v Wade and American fertility". American Journal of Public Health 89(2), pp. 199-203. February 1999.

[20] Lutz, W., Cuaresma, J., Kebede, E., Prskawetz, A., Sanderson, W., Striessnig, E. "Education rather than age structure brings demographic dividend". Proceedings of the National Academy of Sciences of the United States of America 116(26), pp. 12798-12803. June 2019.

[21] Madsen, J., Strulik, H. "Testing unified growth theory: Technological progress and the child quantity-quality tradeoff". Center for European, Governance and Economic Development Research Discussion Papers 393, University of Goettingen, Department of Economics. May 2020.

[22] Newson, L., Postmes, T., Lea, S. E. G., Webley, P. "Why Are Modern Families Small? Toward an Evolutionary and Cultural Explanation for the Demographic Transition". Personality and Social Psychology Review 9(4). November 2005.

[23] Pegou Sibe, J., Chiatchoua, C., Noel Megne, M. "The Long Run Relationship between Population Growth and Economic Growth: a Panel Data Analysis of 30 of the most Populated Countries of the World". Análisis Económico, XXXI(77), pp. 205-218. May-August 2016.

[24] Roberts, M. A. "The Nonidentity Problem". The Stanford Encyclopedia of Philosophy (Summer 2019 Edition), Edward N. Zalta (ed.). Summer 2019.

[25] Shoag, D., Russell, L. Land Use Regulations and Fertility Rates. In: One Hundred Years of Zoning and the Future of Cities, Amnon Lehavi (ed.). Springer. 2018.

[26] Simon, J. The Ultimate Resource. Princeton University Press, ISBN 0-691-00381-5. 1981, rev. 1996.

[27] Stone, L. "Cash for Kids? Assessing the American Family Act". Institute for Family Studies. March 2019.

[28] Stover, J., Winfrey, W. "The effects of family planning and other factors on fertility, abortion, miscarriage, and stillbirths in the Spectrum model". BMC Public Health 17(775). November 2017.

[29] The World Bank. "Fertility rate, total (births per woman)". Accessed June 27, 2020.

[30] Tännsjö, T. "Why We Ought To Accept The Repugnant Conclusion". In: Tännsjö T., Ryberg J. (eds) The Repugnant Conclusion. Library Of Ethics And Applied Philosophy, vol 15. Springer, Dordrecht. 2004.

[31] United Nations, Department of Economic and Social Affairs, Population Division, Population Estimates and Projections Section. "World Population Prospects: The 2017 Revision". Accessed April 18, 2019.

[32] Wesley, E., Peterson, F. "The Role of Population in Economic Growth". SAGE Open 7(4): 2158244017736094. 2017.

[33] World Health Organization. "Total Fertility Rate". Accessed June 27, 2020.

[34] Zaidi, B., Morgan, S. "The Second Demographic Transition Theory: A Review and Appraisal". Annual Review of Sociology 43, pp. 473-492. July 2017.