英语选择 The population problem may be _ one of the world today.A.the most B.most difficult C.the greatest D.more interesting_百度作业帮
英语选择 The population problem may be _ one of the world today.A.the most B.most difficult C.the greatest D.more interesting
A项most不能修饰problem
你自己感觉一下B项最高级前没有加theC项great可以形容problem,表示问题严重D项不对是因为题中没有比较的情境几道英语填空题,请英语高手献身~1.When the police arrived there, the thief had e_______.2.The c_______ have never reached the top of the mountain.3.The i_______ population may be the greatest challenge of the world.4.The s_______ of the houses in the south are quite d_百度作业帮
几道英语填空题,请英语高手献身~1.When the police arrived there, the thief had e_______.2.The c_______ have never reached the top of the mountain.3.The i_______ population may be the greatest challenge of the world.4.The s_______ of the houses in the south are quite d
1.When the police arrived there, the thief had e_______.2.The c_______ have never reached the top of the mountain.3.The i_______ population may be the greatest challenge of the world.4.The s_______ of the houses in the south are quite different from those in the north.
1,escaped2,climbers3,increasing4,style嘿嘿
1.When the police arrived there, the thief had escaped_______.2.The climbers_______ have never reached the top of the mountain.3.The increasing_______ population may be the greatest challenge of the world.4.The structure_______ of the houses in the south are quite different from those in the north
escapedclimbersincreasingstructure
escapedclimbersincreasingstyle中文上面已经给了
这些词的中文意思？1.When the police arrived there, the thief had escaped_______.
2.The climbers_______ have never reached the top of the mountain.
3.The increasing_______ population may be the greatest chall...
第四个我觉得用style更好吧he pollution problem may be __one of the world today.A.the modt B.most difficult Cthe greatest_百度作业帮
he pollution problem may be __one of the world today.A.the modt B.most difficult Cthe greatest
第一个单词是the 吧.选C 污染问题也许是当今世界最大的问题之一.From Wikipedia, the free encyclopedia
For other uses, see .
The distribution of human
A population is a summation of all the
of the same group or , which live in a particular , and have the capability of interbreeding.
In ecology, the population of a certain species in a certain area is estimated using the . The area that is used to define a
population is defined as the area where
is potentially possible between any pair within the area. The probability of interbreeding is greater than the probability of
with individuals from other areas. Under normal conditions, breeding is substantially more common within the area than across the border.
In , population refers to a collection of .
which entails the statistical study of human populations. This article refers mainly to human population.
a sexual population is a set of organisms in which any pair of members can
together. This means that they can regularly exchange gametes to produce normally-fertile offspring, and such a breeding group is also known therefore as a gamodeme. This also implies that all members belong to the same of species, such as humans. 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 : localisation of gamete exchange – through dispersal limitations, or preferential mating, or cataclysm, or other cause – may lead to small actual gamodemes which exchange gametes reasonably uniformly within themselves, but are virtually separated from their neighbouring gamodemes. However, there may be low frequencies of exchange with these neighbours. This may be viewed as 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). 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). Note that 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 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 utilise the effects of dispersion (such as line breeding, pure-line breeding, back-crossing). It can be shown that dispersion-assisted selection leads to the greatest genetic advance (ΔG = change in 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
Main article:
As of today's date, the world population is
to be 7.237 billion./7185 million The US Census Bureau estimates the 7 US billion/7000 million number was surpassed on 12 March 2012. According to a separate estimate by the United Nations, Earth’s population exceeded seven US billion in October 2011, a milestone that offers unprecedented challenges and opportunities to all of humanity, according to , the United Nations Population Fund.
According to papers published by the United States Census Bureau,the world population hit 6.5 US billion/6500 million on 24 February 2006. The
designated 12 October 1999 as the approximate day on which world population reached 6 US billion/6000 million. This was about 12 years after world population reached 5 US billion/5000 million in 1987, and 6 years after world population reached 5.5 US billion/5500 million in 1993. The population of some[] countries, such as , 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 US billion/100 000 million people have probably been born in the last 2000 years.
The years taken for every billion people to be added to the world's population, and the years that population was reached. (with future estimates). See also
alt. chart
Main article:
increased significantly as the
gathered pace from 1700 onwards. The last 50 years have seen a yet more rapid increase in the
of population growth due to
and substantial increases in agricultural productivity, particularly beginning in the 1960s, made by the . In 2007 the
projected that the world's population will likely surpass 10 billion in 2055.
In the future, the world's population is expected to peak, after which it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. According to one report, it 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 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 is often referred to as the .
Main article:
Human population control is the practice of artificially altering the rate of growth of a human population. Historically, human population control has been implemented with the goal of increasing 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, a few programmes, most notably the Chinese government's one-child per family policy, have resorted to coercive measures.
In the 1980s, tension grew between population control advocates and women's health activists who advanced women's
as part of a -based approach. Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1990s.
. Biology Online 2012.
. Oxford Dictionaries. Oxford University Press 2012. a community of animals, plants, or humans among whose members interbreeding occurs
Hartl, Daniel (2007). Principles of Population Genetics. . p. 45.  .
Hartl, Daniel (2007). Principles of Population Genetics. . p. 95.  .
Fisher, R. A. (1999). The Genetical Theory of Natural Selection. .  .
Gordon, Ian L. (2000). "Quantitative genetics of allogamous F2 : an origin of randomly fertilized populations". Heredity 85: 43–52. :.  .
Gordon, Ian L. (2001). "Quantitative genetics of autogamous F2". Hereditas 134 (3): 255–262. :.  .
. BBC News. 24 December .
Haub, C. . "How Many People Have Ever Lived On Earth?" Population Today,
As graphically illustrated by
. BBC News. 29 May .
(Press release). United Nations Population Division. 13 March . The world population continues its path towards population ageing and is on track to surpass 9 billion persons by 2050.
, United Nations, 2011.
Ojovan M.I., Loshchinin M.B. Heuristic Paradoxes of S.P. Kapitza Theoretical Demography. European Researcher, 92 (3), 237-248 (2015).
Shackman, Gene, Xun Wang and Ya-Lin Liu. 2011. Brief review of world population trends. Available at
Knudsen, Lara (2006). . Vanderbilt University Press. p. 2.  .
Knudsen, Lara (2006). . Vanderbilt University Press. pp. 4–5.  .
has a property, , for population (see )
a platform for interaction between research centres and international organizations, such as the United Nations Population Division, ,
(2005). Retrieved 13 February 2005.
. Retrieved 13 February 2004.
. (French)
. (French)
Reports about world and regional population trends
Lee, Ronald Demos (2008). . In
(2nd ed.). Indianapolis: .  .  .
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