In biological science, a population is a group of organisms of the same species that live in the same geographic area at the same time and, for sexually reproducing species, interbreed. A population is dynamic; it changes over time as a result of both biotic (living) and abiotic (non-living) factors. The study of population dynamics is called ecology.

The size of a population is determined by its number and density. A larger population has more genetic variation and therefore greater resilience to unfavorable conditions. A smaller population, on the other hand, has less opportunity to adapt and may be more vulnerable to environmental change. Populations are also characterized by their growth rates, which represent the net annual change in population size resulting from births minus deaths and net immigration minus emigration.

Populations can be defined at various taxonomic levels, including kingdom, phylum/ division, class, order, family, genus and species. The term is sometimes used informally to refer to a group below the level of species. This group is sometimes referred to as an informal sub population, variety, cultivar or strain.

While the concept of populations is often associated with living organisms, it can be applied to any grouping of items that shares a common feature. It is important to understand what the population is being studied or referred to, so that the data can be interpreted correctly. For example, in statistics, a population can be the set of students from which a sample is drawn for a statistical study. It can be easy to confuse this with the entire student body, but a proper definition of population is a grouping based on a significant characteristic that serves as the basis for a statistical study.

Although it is impossible to keep track of the exact number of people alive at any given moment, human populations are growing rapidly and births currently outnumber deaths in most countries. In fact, the world’s population is increasing by roughly 140 people every minute.

The rate of population growth is a major concern for many environmentalists, as it places pressure on natural habitats and resources. Nonetheless, the United Nations believes that moderate population growth can help reduce poverty and improve living standards.

For example, in many western economies, the population is heavily skewed to older retirees, who are placing a heavy burden on social care and healthcare systems. Moderate population growth can rebalance the age distribution and free up funds for other public services. For these reasons, the world’s governments continue to promote healthy fertility rates and educate children on sexual health. In addition, they encourage people to move to areas where housing and services are available at reasonable costs. This helps to alleviate stress on overcrowded urban centers and improve overall quality of life. The population of the world will reach 8 billion in 2022, according to the US Census Bureau. It is expected to increase to 9.7 billion by 2050. This represents a rate of growth of just under 2 percent per year.