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A population pyramid, also called an age pyramid or age picture is a graphical illustration that shows the distribution of various age groups in a population (typically that of a country or region of the world), which forms the shape of a pyramid when the population is growing. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species.
It usually consists of two back-to-back histograms, with the population plotted on the X-axis and age on the Y-axis, one showing the number of males and one showing females in a particular population in five-year age groups (also called cohorts). Males are conventionally shown on the left and females on the right, and they may be measured by raw number or as a percentage of the total population.
Population pyramids are often viewed as the most effective way to graphically depict the age and sex distribution of a population, partly because of the very clear image these pyramids represent.
A great deal of information about the population broken down by age and sex can be read from a population pyramid, and this can shed light on the extent of development and other aspects of the population. A population pyramid also tells how many people of each age range live in the area. There tends to be more females than males in the older age groups, due to females' longer life expectancy.
While all countries' population pyramids differ, the following general types have been identified by the fertility and mortality rates of a country.
- "Stationary" pyramid
- A population pyramid has roughly equal numbers of people in most age categories, with tapering for older ages. Countries with relatively low constant birth rates and high life quality exhibit a stationary pyramid.
- "Expansive" pyramid
- A population pyramid that is very wide at the younger ages, characteristic of countries with high birth rate and low life expectancy.
- "Constrictive" pyramid
- A population pyramid that is narrowed at the bottom. The population is generally older on average, as the country has long life expectancy, a low death rate, but also a low birth rate. This pyramid is becoming more common, especially when immigrants are factored out, and is a typical pattern for a very developed country, a high level of education, easy access to and incentive to use birth control, good health care, and few negative environmental factors.
In some countries the above "pyramids" are referred to by a description of their shape. The classic example is the pyramid. The stationary pyramid is referred to as a "clock-model" (like the bell in a clock tower). The contracting pyramid is referred to as "onion" shaped, or occasionally as "urn" shaped.
The expansive case was described as youth bulge by Gary Fuller (1995). Gunnar Heinsohn (2003) argues that an excess in especially young adult male population predictably leads to social unrest, war and terrorism, as the "third and fourth sons" that find no prestigious positions in their existing societies rationalize their impetus to compete by religion or political ideology.
Heinsohn claims that most historical periods of social unrest lacking external triggers (such as rapid climatic changes or other catastrophic changes of the environment) and most genocides can be readily explained as a result of a built-up youth bulge, including European colonialism, 20th-century fascism, rise of Communism during the Cold War, and ongoing conflicts such as that in Darfur and terrorism. This factor has been also used to account for the Arab Spring events. Economic recessions, such as the Great Depression of the 1930s and the Late 2000's recession, are also claimed to be explained in part due to a large youth population who cannot find jobs. Youth bulge can be seen as one factor among many in explaining social unrest and uprisings in society. A 2016 study finds that youth bulges increase the chances of non-ethnic civil wars, but not ethnic civil wars.
A large population of adolescents entering the labor force and electorate strains at the seams of the economy and polity, which were designed for smaller populations. This creates unemployment and alienation unless new opportunities are created quickly enough – in which case a 'demographic dividend' accrues because productive workers outweigh young and elderly dependents. Yet the 16–30 age range is associated with risk-taking, especially among males. In general, youth bulges in developing countries are associated with higher unemployment and, as a result, a heightened risk of violence and political instability. For Cincotta and Doces (2011), the transition to more mature age structures is almost a sine qua non for democratization.
Population pyramid of Egypt in 2005. Many of those 30 and younger are educated citizens who are experiencing difficulty finding work.
Nearly half of Libya's 2011 population consists of children younger than age 20.
The Middle East and North Africa
The Middle East and North Africa are currently experiencing a prominent youth bulge. "Across the Middle East, countries have experienced a pronounced increase in the size of their youth populations over recent decades, both in total numbers and as a per- centage of the total population. Today, the nearly 111 million individuals aging between 15 to 29 living across the region make up nearly 27 percent of the region’s population."  Structural changes in service provision, especially health care, beginning in the 1960s created the conditions for a demographic explosion, which has resulted in a population consisting primarily of younger people. It is estimated that around 65% of the regional population is under the age of 30.
The Middle East has invested more in education, including religious education, than most other regions such that education is available to most children. However, that education has not led to higher levels of employment, and youth unemployment is currently at 25%, the highest of any single region. Of this 25%, over half are first time entrants into the job market.
The youth bulge in the Middle East and North Africa has been favorably compared to that of East Asia, which harnessed this human capital and saw huge economic growth in recent decades. The youth bulge has been referred to by the Middle East Youth Initiative as a demographic gift, which, if engaged, could fuel regional economic growth and development. "While the growth of the youth population imposes supply pressures on education systems and labor markets, it also means that a growing share of the overall population is made up of those considered to be of working age; and thus not dependent on the economic activity of others. In turn, this declining dependency ratio can have a positive impact on overall economic growth, creating a demographic dividend. The ability of a particular economy to harness this dividend, however, is dependent on its ability to ensure the deployment of this growing working-age population towards productive economic activity, and to create the jobs necessary for the growing labor force." 
- Population pyramids of the world from 1950 to 2050
- Department of Health Home
- http://www.fsl.orst.edu/pnwerc/wrb/Atlas_web_compressed/5.Human_Populations/5h.pyramids_web.pdf Population Pyramids - Oregon State University
- Korotayev A. et al.A Trap At The Escape From The Trap? Demographic-Structural Factors of Political Instability in Modern Africa and West Asia. Cliodynamics 2/2 (2011): 1-28.
- The Effects of 'Youth Bulge' on Civil Conflicts - Council on Foreign Relations
- Yair, Omer; Miodownik, Dan (2016-02-01). "Youth bulge and civil war: Why a country's share of young adults explains only non-ethnic wars". Conflict Management and Peace Science. 33 (1): 25–44. doi:10.1177/0738894214544613. ISSN 0738-8942.
- Huntington, Samuel P. 1996. The Clash of Civilizations and the Remaking of World Order. New York, NY: Simon and Schuster
- Urdal, Henrik. 2006. "A Clash of Generations? Youth Bulges and Political Violence." International Studies Quarterly 50:607-29 doi:10.1111/j.1468-2478.2006.00416.x
- Cincotta, Richard, and John Doces. 2011. "The Age-structural Maturity Thesis: The Youth Bulge's Influence on the Advent and Stability of Liberal Democracy?" In Political Demography: identity, conflict and institutions ed. J. A. Goldstone, E. Kaufmann and M. Toft. Boulder, CO: Paradigm Press
- Hassan, Islam; Dyer, Paul (2017). "The State of Middle Eastern Youth." (PDF). The Muslim World. 107 (1): 3–12.
- Navtej Dhillon "The Role of the U.S. in the Middle East," Congressional Briefing (May 2008)
- Navtej Dhillon, Tarik Yousef. "Inclusion: Meeting the 100 Million Youth Challenge"
- Middle East Youth Initiative – Employment
- Navtej Dhillon, Tarik Yousef. "Inclusion: Meeting the 100 Million Youth Challenge" (2007)
- "Youth – An Undervalued Asset: Towards a New Agenda in the Middle East and North Africa, Progress, Challenges and Way Forward," Middle East and North Africa Region Human Development Department (MNSHD), The World Bank, 2007" (PDF). Retrieved 27 October 2011.
- "Middle East Youth Initiative: About: Why Shabab?". Retrieved 27 October 2011.
- Gary Fuller, "The Youth Crisis in Middle Eastern Society" (2004) download
- Gary Fuller, The Demographic Backdrop to Ethnic Conflict: A Geographic Overview, was born in 1989 and was produced by Edward Gewin: The Challenge of Ethnic Conflict to National and International Order in the 1990s, Washington: CIA (RTT 95-10039, October), 151-154.
- Heinsohn, Gunnar (2003). Söhne und Weltmacht : Terror im Aufstieg und Fall der Nationen (in German). Zürich: Orell Füssli. ISBN 3-280-06008-7.
- Navtej Dhillon, "Middle East Youth Bulge: Challenge or Opportunity?" (2008) The Brookings Institution
- "From Oil Boom to Youth Boon: Tapping the Middle East Demographic Gift" (2008) The Brookings Institution
- Graham Fuller, "The Youth Factor: The New Demographics of the Middle East and the Implications for U.S. Policy" (2003) The Brookings Institution
- The Security Demographic: Population and Civil Conflict after the Cold War
- The "Youth Bulge" (zmag.org)
- The Shape of Things to Come, Why Age Structure Matters To A Safer, More Equitable World
- Political Demography: identity, conflict and institutions ed. J. A. Goldstone, E. Kaufmann and M. Toft. Boulder, CO: Paradigm Press
|Wikimedia Commons has media related to Population pyramids.|
- World Population Prospects, the 2010 Revision, Website of the United Nations Population Division with population pyramids for all countries
- U.S. Census Bureau, International Statistical Agencies
- U.S. Census Bureau, International Database (IDB)
- United Nations Data Set Population pyramids from 1950 to 2050
- Australian animated population pyramids, Australian Bureau of Statistics
- Interactive population pyramids of metropolitan France 1901-2060 (INSEE)
- China, Europe, USA: Population by Age and Sex, 1950-2050. Moving Age pyramids.
- A discussion on population pyramids as a data visualization tool