Terms

Population Problems

Terms and Concepts

Image by permission from 6 milliards d'Hommes / 6 billion Human Beings

Basic Forces: Fertility
Mortality
Migration
Constraints: Carrying Capacity
Descriptive and Analytical Concepts: Age Structure
Sex Structure
Growth Rates and Doubling Time
Life Expectancy and Life Chances
Nuptuality
Demographic Transition
Policy: Family Planning

Fertility (Stacy Fuchs): Fertility is the condition, quality, and degree of being fertile for an individual; it also refers to the birthrate of an entire population. The fertility of individuals determines the fertility of a nation. Fertility is measured by total fertility rate, TFR. TFR is the average number of children a woman will have in her lifetime. Fertility is determined by a number of factors including onset of fecundity (fertility or the ability to get pregnant), degree of fecundity, incidence of miscarriage, duration of temporary infecundity following a birth, length of breast feeding, age of onset of permanent sterility, social behavior and cultural restrictions. Fertility is imperative to the study of population because it determines the natural increase in a population. Mortality and fertility combine to determine the natural growth or decline of a population.

Mortality (Korin Werner): The term "mortality" has two possible meanings: the state of being susceptible to death and also the relative number of deaths within a given population. These two definitions are not entirely separate from each other, but are actually inherently linked. Social/cultural factors (ex: methods of childrearing), economic factors (ex: improved quality of life), and medical/scientific advances combine to improve an individual's chances for longevity (the first definition). When individuals live longer, the result is a lower rate of mortality for the population as a whole (the second definition).
Mortality is an important concept in the study of population because it is a large factor in the growth or decline of a civilization. High mortality rates make a population more susceptible to decline, and perhaps even to extinction. On the other hand, low mortality rates can mean the possibility of overpopulation, which could in turn lead to starvation and other negative consequences. Mortality rates can actually be somewhat cyclical: somewhat high mortality rates can result in extra resources for those still left alive, giving them lower mortality rates. In turn these lower mortality rates can lead to overpopulation, which can have negative consequences…

Migration (Kennon Bauman): Migration can be defined as a move from one region to another, permanently or temporarily. In most population-related situations, migration refers to more permanent movements. There are two parts of migration: immigration and emigration. Emigration refers to people (either as large groups, or as individuals) leaving their current homes, while immigration refers to the arrival of émigrés to their destination. Which part of migration effects a particular country or region depends greatly upon various "push factors" and "pull factors." Countries with many resources and economic opportunities pull in populations. Nations with few resources, limited civil liberties, or little chance for economic growth tend to push people away. Overcrowding or a lack of needed resources are examples of push factors, while higher standards of living or open land serve as pull factors. Although migrations of large populations from one place to another are no longer as common as they once were, these movements can drastically influence the population of any area. A sudden rush of immigrants can strain resources, just as constant emigration can leave a region without the people it needs to support itself. From the immigrations of the Goths and Visigoths to the regions north of Rome, to the massive influx of European populations to the United States at the beginning of the twentieth century, migration can have drastic effects upon the social, political, agricultural, and military situations of any nation or region.

Carrying Capacity (Ben Aaker): From an ecological standpoint, carrying capacity is the total amount of organisms a region can hold indefinitely without causing permanent damage to the ecosystem. When speaking of populations of human beings, carrying capacity must be defined by a different criterion. Carrying capacity then becomes the maximum population supported indefinitely by current food production and waste management without causing permanent damage to the ecosystem. It should be noted that, while humans damage the environment, most damage is not permanent. Carrying capacity has increased accordingly throughout human history as advances in agriculture and technology have improved. Current estimates for Earth's carrying capacity range from 10 to 100 billion humans.

Age Structure (Chris Dabney): The age structure of a population refers to the distribution of persons into categories of varying ages, with the relative sizes of such categories typically arranged chronologically in increments of five to ten years. Age structures are easily visualized and are often implemented as a useful tool for recognizing trends in changing populations, as well as aiding, to some extent, in the analysis of the impact of social events on the birth and mortality rates of a population, among other trends. Age structure charts are often used in combination with sex structure charts to form a more complete view of a society's population. The sample chart offered below is an example of one such combination chart.


Sex Structure (Tabitha Lurz): A sex structure displays the sex distribution measured by the ratio of the total number of one sex to the total population or to the total number of the other sex. It also shows the growth potential of a population because population growth is directly related to the number of fertile women in a population. A sex structure is often used in combination with an age structure or other categories to show a greater breakdown of the males and females in a population. The other categories, such as education level, salaries, etc., enable a comparison of the sexes and the evaluation of the effects that such differences or similarities have on the population and economy.
The chart above shows the age/sex structure of the United States in 2000. In 1990 there were 121,239,418 males and 127,470,455 females in the United States for a F:M ratio of 1:1.05.

Growth Rates and Doubling Time (Justin Kopetsky): The growth rate of a nation, state, or entire world is the rate at which its population is changing. The rate, presented as a percent change, may be either positive or negative indicating a gain or a loss of population. The growth rate is governed by birth and death rates in the context of the world. If there are more births than deaths, the rate will be positive. A negative rate is the product of more deaths than births. It is also possible, but not probable that the growth rate would be zero. This would result in neither a gain nor a loss in population. On a more localized level immigration and emigration are also large factors. Large numbers of people entering or leaving a nation can have a dramatic effect on the population. World-wide, immigration has no effect because there is no large population leaving the earth or entering it.
Doubling time is directly related to the growth rate. Doubling time is the amount of years that it will take for a certain population to double in size from a specified date. It is calculated much the same way as an investment in a bank. The easiest way to calculate this is by dividing 70 by the growth rate. This gives you a fairly accurate estimate of the doubling time for any given population.

Life Expectancy and Life Chances (Ben Tesch): A figure representing the number of years, based on known statistics, to which any person of any given age may reasonably expect to live. Life expectancy is influenced by a number of factors, the most important being biological, social, and environmental. The trend of lengthened life expectancy since the Industrial Revolution is linked to immaterial progress, such as changes in individual behavior and scientific advancement, and not to material progress, such as greater economic wealth.

Nuptuality (Lindsey Tilberg)

Nuptuality may be defined as the rate of marriage among a population. Divorce, mortality, and the practice of polygamy as well as standard of living and economic problems all affect this rate. Marriage rate, in turn, affects population. If a population has many unmarried people who pass the reproductive years (assuming a small percentage of unmarried people having children), the reproduction rate is going to go down and eventually may cause extinction of the group. Marriage rate is sometimes misrepresented. While it is higher in the United States than in many other countries, it often goes unreported in areas where common-law marriages are legal and also in areas where reports may be incomplete or inaccurate. Nuptuality needs to be taken into consideration when looking at a population, but social views of marriage also need to be looked at in order to see how nuptuality truly affects the population.

Demographic Transition (Colleen Kelley)

The term demographic transition generally refers to the model/theory of population development that seeks to explain a nation's transition from high birth and death rates to low birth and death rates. The model compares a nation's crude birth rate (CBR) to its crude death rate (CDR) over time (CBR or CDR= [# of births (or deaths) in one year/total population] x1000). The demographic transition model is based on the actual demographic history of population in England, and has been an adequate description of the transition in many developed countries. The model usually consists of four stages (though some consider that there are five, four remains a constant, accepted transition), and a nation's social and economic status generally indicates what stage that nation is in:

I. High CBR and CDR; common in pre-industrial societies and undeveloped nations. Overall population experiences little change.
II. CBR remains high while CDR begins to lower; many 3rd world or developing nations are in this stage. Overall population growth occurs during this stage.
III. CBR begins to lower and CDR remains low; this stage includes 2nd world countries such as China. Overall population growth occurs during this stage.
IV. Low CBR and CDR; many developed nations, such as the US and England, are entering or are already in this stage, which sees the stabilization of a population.

Family Planning (Wade Sirles)

Advising people on all of the options of parenting, such as becoming a parent or remaining childless, as well as promoting and educating the use of contraceptives and other pregnancy avoidance methods in order to help determine (plan) the time of pregnancy. Planned Parenthood tries to reduce the number of unwanted pregnancies and help people become parents who lack the ability to conceive children.

Urbanization (Michael Harkness)

Urbanization is the transition of a population from an agricultural to a non agricultural basis. Urbanization often results from high levels of industrialization and is frequently associated with prosperity. Urban areas are demographically self-sustaining, but are dependent upon other regions for food.

Last update: 15 May 2001