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25-410: The Wiltshire Horn is a breed of domestic sheep originally from Wiltshire in southern England raised for meat . The breed is unusual among native British breeds, for it has the unusual feature of moulting its short wool and hair coat naturally in spring, obviating the need for shearing . They are good mothers and have high fertility. The Wiltshire Horn was until the eighteenth century one of

50-408: A sexual population is the area where interbreeding is possible between any opposite-sex pair within the area and more probable than cross-breeding with individuals from other areas. In humans , interbreeding is unrestricted by racial differences, as all humans belong to the same species of Homo sapiens. In ecology, the population of a certain species in a certain area can be estimated using

75-476: A few programs, most notably the Chinese government's one-child per family policy, have resorted to coercive measures. In the 1970s, tension grew between population control advocates and women's health activists who advanced women's reproductive rights as part of a human rights -based approach. Growing opposition to the narrow population control focus led to a significant change in population control policies in

100-476: Is a hair breed, growing a thick, coarse coat in the winter and shedding in the summer. Rams weigh about 250 lb (110 kg) and ewes 150 lb (68 kg). No longer a rare breed, the Wiltshire Horn is proving its worth to three particular groups of producers: Breed Another point of view is that a breed is consistent enough in type to be logically grouped together and when mated within

125-476: Is derived from the Latin word populus (a people). In sociology and population geography , population refers to a group of human beings with some predefined feature in common, such as location, race , ethnicity , nationality , or religion . In ecology , a population is a group of organisms of the same species which inhabit the same geographical area and are capable of interbreeding . The area of

150-609: Is not even known to the nearest million, so there is a considerable margin of error in such estimates. Researcher Carl Haub calculated that a total of over 100 billion people have probably been born in the last 2000 years. Population growth increased significantly as the Industrial Revolution gathered pace from 1700 onwards. The last 50 years have seen a yet more rapid increase in the rate of population growth due to medical advances and substantial increases in agricultural productivity, particularly beginning in

175-611: Is often referred to as the demographic transition . Human population planning is the practice of altering the rate of growth of a human population. Historically, human population control has been implemented with the goal of limiting the rate of population growth. In the period from the 1950s to the 1980s, concerns about global population growth and its effects on poverty, environmental degradation , and political stability led to efforts to reduce population growth rates. While population control can involve measures that improve people's lives by giving them greater control of their reproduction,

200-715: Is very likely that the world's population will stop growing before the end of the 21st century. Further, there is some likelihood that population will actually decline before 2100. Population has already declined in the last decade or two in Eastern Europe, the Baltics and in the former Commonwealth of Independent States. The population pattern of less-developed regions of the world in recent years has been marked by gradually declining birth rates. These followed an earlier sharp reduction in death rates. This transition from high birth and death rates to low birth and death rates

225-478: The Lincoln index to calculate the total population of an area based on the number of individuals observed. In genetics, a population is often defined as a set of organisms in which any pair of members can breed together. They can thus routinely exchange gametes in order to have usually fertile progeny, and such a breeding group is also known therefore as a gamodeme. This also implies that all members belong to

250-569: The 1960s, made by the Green Revolution . In 2017 the United Nations Population Division projected that the world's population would reach about 9.8 billion in 2050 and 11.2 billion in 2100. In the future, the world's population is expected to peak at some point, after which it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. According to one report, it

275-496: The United States Census Bureau, the world population hit 6.5 billion on 24 February 2006. The United Nations Population Fund designated 12 October 1999 as the approximate day on which world population reached 6 billion. This was about 12 years after the world population reached 5 billion in 1987, and six years after the world population reached 5.5 billion in 1993. The population of countries such as Nigeria

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300-480: The breaking up of a large sexual population (panmictic) into smaller overlapping sexual populations. This failure of panmixia leads to two important changes in overall population structure: (1) the component gamodemes vary (through gamete sampling) in their allele frequencies when compared with each other and with the theoretical panmictic original (this is known as dispersion, and its details can be estimated using expansion of an appropriate binomial equation ); and (2)

325-620: The breed suffer a dramatic decline throughout the 19th and 20th centuries. It was nearly extinct at the start of the 1900s. In 1923, in an attempt to save the breed, the Wiltshire Horn Breed Society was formed. In the early 1980s, 45 registered flocks were in the UK, but the 2009 edition of the flock book of the Wiltshire Horn Sheep Society recognises almost 300 flocks. The Wiltshire Horn is one of

350-484: The breeder mates the most desirable representatives of the breed from his or her point of view, aiming to pass such characteristics to their progeny . This process is known as selective breeding . A written description of desirable and undesirable breed representatives is referred to as a breed standard . Breed specific characteristics, also known as breed traits, are inherited, and purebred animals pass such traits from generation to generation. Thus, all specimens of

375-607: The foundation breeds for Katahdin , Wiltipoll , and Easycare breeds and the Hampshire breed along with Southdown sheep and the Berkshire Nott. Until the 20th century, the breed was chiefly traded at local events such as the Westbury Hill Fair . Males and females both have horns. Ram horns grow one full spiral each year until maturity. Both sexes are white with occasion black spots on the undercoat. This

400-494: The group produce the same type. When bred together, individuals of the same breed pass on these predictable traits to their offspring, and this ability – known as " breeding true " – is a requirement for a breed. Plant breeds are more commonly known as cultivars . The offspring produced as a result of breeding animals of one breed with other animals of another breed are known as crossbreeds or mixed breeds. Crosses between animal or plant variants above

425-455: The level of breed/cultivar (i.e. between species, subspecies , botanical variety , even different genera ) are referred to as hybrids . The breeder (or group of breeders) who initially establishes a breed does so by selecting individual animals from within a gene pool that they see as having the necessary qualities needed to enhance the breed model they are aiming for. These animals are referred to as foundation stock . Furthermore,

450-463: The level of homozygosity rises in the entire collection of gamodemes. The overall rise in homozygosity is quantified by the inbreeding coefficient (f or φ). All homozygotes are increased in frequency – both the deleterious and the desirable. The mean phenotype of the gamodemes collection is lower than that of the panmictic original – which is known as inbreeding depression. It is most important to note, however, that some dispersion lines will be superior to

475-458: The number of people in a single area. Governments conduct a census to quantify the size of a resident population within a given jurisdiction. The term is also applied to non-human animals , microorganisms , and plants , and has specific uses within such fields as ecology and genetics . The word population is derived from the Late Latin populatio (a people, a multitude), which itself

500-418: The panmictic original, while some will be about the same, and some will be inferior. The probabilities of each can be estimated from those binomial equations. In plant and animal breeding , procedures have been developed which deliberately utilize the effects of dispersion (such as line breeding, pure-line breeding, backcrossing). Dispersion-assisted selection leads to the greatest genetic advance (ΔG=change in

525-771: The phenotypic mean), and is much more powerful than selection acting without attendant dispersion. This is so for both allogamous (random fertilization) and autogamous (self-fertilization) gamodemes. According to the UN, the world's population surpassed 8 billion on 15 November 2022, an increase of 1 billion since 12 March 2012. According to a separate estimate by the United Nations, Earth's population exceeded seven billion in October 2011. According to UNFPA , growth to such an extent offers unprecedented challenges and opportunities to all of humanity. According to papers published by

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550-468: The predominant sheep breeds of southern England. For hundreds of years, it served a clear function on the thin chalk soils of the Wiltshire Downs, requiring little shelter from the elements and providing dung and urine to fertilise the wheat-growing land. At the same time, it provided an easily managed source of quality meat, but the rising price of wool and a general move away from horned sheep had

575-430: The same breed carry several genetic characteristics of the original foundation animal(s). In order to maintain the breed, a breeder would select those animals with the most desirable traits to achieve further maintenance and developing of such traits. At the same time, the breed would avoid animals carrying characteristics undesirable or not typical for the breed, including faults or genetic defects. The population within

600-422: The same breed should consist of a sufficient number of animals to maintain the breed within the specified parameters without the necessity of forced inbreeding . Domestic animal breeds commonly differ from country to country, and from nation to nation. Breeds originating in a certain country are known as "native breeds" of that country. Population Population is the term typically used to refer to

625-829: The same species. If the gamodeme is very large (theoretically, approaching infinity), and all gene alleles are uniformly distributed by the gametes within it, the gamodeme is said to be panmictic. Under this state, allele ( gamete ) frequencies can be converted to genotype ( zygote ) frequencies by expanding an appropriate quadratic equation , as shown by Sir Ronald Fisher in his establishment of quantitative genetics. This seldom occurs in nature: localization of gamete exchange – through dispersal limitations, preferential mating, cataclysm, or other cause – may lead to small actual gamodemes which exchange gametes reasonably uniformly within themselves but are virtually separated from their neighboring gamodemes. However, there may be low frequencies of exchange with these neighbors. This may be viewed as

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