As the death rate declines, more people survive to the reproductive ages and beyond. This shape is the result of high birth rates that feed more and more people into the lowest bars and in turn shrink the relative proportion at the oldest ages. The first pyramid, representing the population of the Democratic Republic of Congo, with its wide base and narrow top, is typical of a young population. The country pyramids shown in “Three Patterns of Population Change” also represent different stages of population growth going on today. The horizontal bars show the percentage (or in some cases the actual numbers) of males and females in each age group. The four representations of population age-sex structure provide an overall example of what a pyramid for different levels of population growth would look like - rapid growth, slow growth, zero growth, and negative growth. The overall shape of the pyramid indicates the potential for future growth. The age-sex structure of a country can be studied through population pyramids. Thus, even though it has reached replacement level fertility, China’s population continues to grow. This momentum is very pronounced in China, where women have about two children, but the number of women having children is now much larger than in the previous generation. The momentum of population growth in less developed countries will only be slowed when the large number of young adults resulting from previous high fertility have passed out of the childbearing years and a succeeding smaller generation reproduces at replacement level fertility. Hispanics, 40 percent of whom are foreign-born, there are approximately 10 births for every death. Immigrants, who are younger on average than the U.S.-born population, play a significant role in keeping the United States younger than most other developed countries. In the United States, birth rates are higher than death rates at present, partly due to the relatively young age structure of the U.S. This phenomenon is known as population momentum. Hence, a relatively large number of couples each having one or two children can still produce a large excess of births. If there are comparatively more young adults than older adults where mortality is highest, then even at replacement fertility levels (when each woman has about an average of two children) there will be more births than deaths. ![]() Births occur primarily to people in the younger-adult age groups. The rate of natural increase of a population depends on birth and death rates, which are strongly influenced by the population age structure. This rate of natural increase occurred in spite of a very small average family size measured by the total fertility rate-an estimate of the number of births to women during their lifetimes. birth rate in 2005 was 14 births per 1,000 people and the death rate was 8, yielding a net increase of six persons for every 1,000 persons in the United States, or approximately 1.7 million additional persons for that year. Growth through natural increase occurs when the birth rate exceeds the death rate. Question and Answer: Why Does It Take So Long to Slow or Stop Population Growth? ![]() Our Commitment to Diversity, Equity, and Inclusion.Policy and Advocacy Communications Training. ![]() Management of Complex Technical Programs.Distilling Research for Non-Technical Audiences.Adaptive Learning and Knowledge Management.Family Planning, Maternal and Reproductive Health.
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