What do populations makeup

As a result, in each county type, adults ages 65 and older now make up a larger share of the total population than in The nation is becoming more racially and ethnically diverse, but these changes have been more muted in rural counties compared with urban and suburban ones. The white share of the population fell 8 percentage points since in the suburbs, 7 points in the urban core and only 3 points in rural counties.

Overall, the U. While the share of the non-Hispanic whites has declined, the number of whites grew in the nation overall — and in suburban counties as a whole — since But the white population did not grow as sharply as other groups did, leading to a decline in the white share of the total U. In urban counties, the decline in the share of the white population was due both to a decrease in the number of whites and an increase in the size of other populations, chiefly Hispanics.

In rural counties, the white population also decreased and other groups also increased in size, but the impact was more modest on the white share of the population because whites are so large a proportion of rural residents. The foreign-born population is not evenly distributed across county types; immigrants tend to be concentrated in big metropolitan areas. In fact, about half live in urban counties, where they make up a higher share of the total than in suburban or rural counties.

The immigrant share of the population grew since in the nation as a whole and in each county type. Although rural counties as a group have more U. There is a large overlap between rural counties that have fewer U.

In the vast majority of rural counties that lost population — 1, out of 1, — the number of U. In addition to the three major demographic shifts that are reshaping urban, suburban and rural counties in the U. These relate to the economic well-being of their residents. Poverty rates have risen in all three county types since The number of people living in poverty also has risen across community types, but the size of the poor population rose more sharply in suburban counties than in urban or rural ones.

About half the U. But looking at the share of counties where at least a fifth of the population is poor — a measure known as concentrated poverty — rural areas are at the top. The number of counties with concentrated poverty grew for all three county types since Growing shares of residents ages 25 and older have graduated from college in all types of U.

Rural communities lag in the share of the population with a college degree. Rural areas also trail urban and suburban areas in their share of residents with postgraduate degrees.

In urban and suburban counties overall, college graduates outnumber residents with a high school diploma and no further education, but in the total rural population there are more high school graduates than college graduates. The share of residents who did not graduate from high school has dwindled in all three county types.

Rural counties also trail other types of communities, especially urban counties, on key measures of employment of prime-age workers — those 25 to 54 years old. By , the number of Muslims will nearly equal the number of Christians.

In the U. The demographic future for the U. Growth from to was rapid — the global population nearly tripled, and the U. However, population growth from to is projected to be significantly slower and is expected to tilt strongly to the oldest age groups , both globally and in the U. Public opinion on whether the growing number of older people is a problem varies dramatically around the world. Concern is highest in East Asia where large majorities describe aging as a major problem for their countries.

In times of uncertainty, good decisions demand good data. Please support our research with a financial contribution. It organizes the public into nine distinct groups, based on an analysis of their attitudes and values.

Even in a polarized era, the survey reveals deep divisions in both partisan coalitions. Pew Research Center now uses as the last birth year for Millennials in our work. President Michael Dimock explains why.

The vast majority of U. Use this tool to compare the groups on some key topics and their demographics. About Pew Research Center Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. Key Concepts genetic variation species. Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2.

The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Postcards from the Universe. Brain Metrics. How do populations respond to all these forces? As relative allele frequencies change, relative genotype frequencies may also change.

Each genotype in the population usually has a different fitness for that particular environment. In other words, some genotypes will be favored, and individuals with those genotypes will continue to reproduce. Other genotypes will not be favored: individuals with those genotypes will be less likely to reproduce.

What type of genotype would be unfavorable? Unfavorable genotypes take many forms, such as increased risk of predation, decreased access to mates, or decreased access to resources that maintain health. Overall, the forces that cause relative allele frequencies to change at the population level can also influence the selection forces that shape them over successive generations. For example, if moths with genotype aa migrate into a population composed of AA and Aa individuals, they will increase the relative allele frequency of a.

However, if the aa genotype has a clear disadvantage to survival e. This page appears in the following eBook. Aa Aa Aa. Genetic variation describes naturally occurring genetic differences among individuals of the same species. This variation permits flexibility and survival of a population in the face of changing environmental circumstances.

Consequently, genetic variation is often considered an advantage, as it is a form of preparation for the unexpected. But how does genetic variation increase or decrease? And what effect do fluctuations in genetic variation have on populations over time? Mating patterns are important. Random forces lead to genetic drift. If the individuals at either end of the range reconnect and continue mating, the resulting genetic intermixing can contribute to more genetic variation overall.

However, if the range becomes wide enough that interbreeding between opposite ends becomes less and less likely, and the different forces acting at either end become more and more pronounced, and the individuals at each end of the population range may eventually become genetically distinct from one another.