A population bottleneck (or genetic bottleneck) is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing, and the population is reduced by 50% or more, often by several orders of magnitude. A graph of a function of this change resembles the neck of a bottle, from wide to narrow; hence the name. Population bottlenecks increase genetic drift, as the rate of drift is inversely proportional to the population size. It also changes the relationship of natural selection (see: inbreeding). ==Humans== DNA evidence suggests that humans today are a legacy of a population bottleneck which occurred 70,000 years ago. This would have had the result of limiting the overall level of genetic diversity in the human species, possibly by a large amount. The evidence that all living humans are descended from fewer than ten thousand people alive at that time comes both from mitochondrial DNA coalescence, and the relatively small variations in the human Y chromosome. One theory about this bottleneck is the Toba catastrophe theory, positing that the human population was reduced to a few thousand individuals when the Lake Toba supervolcano in Indonesia erupted and triggered a massive environmental change. In 2000, a ''Molecular Biology and Evolution paper'' suggested a transplanting model or a 'long bottleneck' to account for the limited genetic variation, rather than a catastrophic environmental change. (See "[http://mbe.oupjournals.org/cgi/content/full/17/1/2 ''Population Bottlenecks and Pleistocene Human Evolution'']".) ==Examples in the animal world== {| style="float:right; border:1px solid;" cellspacing=2 cellpadding=2 |- |Year||Estimated bison
population size |- |Before 1492 |align="right"| 60,000,000 |- |1890 |align="right"| 750 |- |2000 |align="right"| 3,600 |} Wisent, also called European bison, faced extinction in the early 20th century. The 3600 animals living in 2000 are all descended from 12 individuals and only two distinct Y chromosomes are left in the species. The population of American Bison fell due to overhunting, nearly leading to extinction around the year 1890 and has since begun to recover. A classic example of a population bottleneck is that of the northern elephant seals, whose population fell to about 30 in the 1890's although it now numbers in the tens of thousands. Also, all existing cheetahs are extremely close genetically suggesting an extreme population bottleneck in the past. Another largely bottlenecked species is the Golden hamster, for which the vast majority are descended from a single litter found in the Syrian desert around 1930. Sometimes further deductions can be inferred from an observed population bottleneck. Among the Galapagos archipelago's giant tortoises (themselves a prime example of a founder effect), the comparatively large population on the slopes of Alcedo volcano is significantly less diverse than four other tortoise populations on the same island. Researchers' DNA analysis dates the bottleneck around 88,000 years before present (YBP), according to a notice in ''Science,'' October 3, 2003. About 100,000 YBP the volcano erupted violently, burying much of the tortoise habitat deep in pumice and ash. The coincidence is suggestive. ==See also== *Small population size * effective population size *Founder effect *Overpopulation *Ice age *Black Death *AIDS *Toba catastrophe theory ==External links== * http://www.sciencedaily.com/releases/2000/01/000110142554.htm *[http://www.sealexperience.com/docs/protect.htm Northern elephant seals] *http://essp.csumb.edu/eseal/kristi_west/history.html Population genetics Human evolution
From the article: :All species being survivors in relation to the levels their environment support, there is reasonable thinking that says human beings are due for another bottleneck sometime soon. Really? Please provide cites that this thinking is mainstream. --------------------- Also, AIDS, whilst a disastrous pandemic, is not anywhere near the level needed for a bottleneck. :Not globally, but it is approaching (and projected to reach) that level in parts of Africa. (The Black Death was only a regional phenomenon, too.) User:Mkweise ---- "From a bunch to a bushel" sounds poetic, but I think will lose some readers (even some fluent in English) -- can someone find a better way to say this? User:Slrubenstein :I think a loss of at least 50% qualifies, but I'm not sure. If anyone knows better, please fix the article. User:Mkweise 01:23 23 May 2003 (UTC) What is "ybp"? Uncommon abbreviations should either be spelled out in full the first time they are used in an article, or they should be linked to a glossary entry. :"Years before present" should be spelled out in full at the first encounter.--User:Wetman 12:52, 12 Mar 2005 (UTC) ----- ''"as the rate of drift is inversely proportional to the population size."'' No, the rate of drift is a constant. This needs rethinking as well as rephrasing. --User:Wetman 12:52, 12 Mar 2005 (UTC)
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Population bottleneck
A population bottleneck (or genetic bottleneck) is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing, and the population is reduced by 50% or more, often by several orders of magnitude. A graph of a function of this change resembles the neck of a bottle, from wide to narrow; hence the name. Population bottlenecks increase genetic drift, as the rate of drift is inversely proportional to the population size. It also changes the relationship of natural selection (see: inbreeding). ==Humans== DNA evidence suggests that humans today are a legacy of a population bottleneck which occurred 70,000 years ago. This would have had the result of limiting the overall level of genetic diversity in the human species, possibly by a large amount. The evidence that all living humans are descended from fewer than ten thousand people alive at that time comes both from mitochondrial DNA coalescence, and the relatively small variations in the human Y chromosome. One theory about this bottleneck is the Toba catastrophe theory, positing that the human population was reduced to a few thousand individuals when the Lake Toba supervolcano in Indonesia erupted and triggered a massive environmental change. In 2000, a ''Molecular Biology and Evolution paper'' suggested a transplanting model or a 'long bottleneck' to account for the limited genetic variation, rather than a catastrophic environmental change. (See "[http://mbe.oupjournals.org/cgi/content/full/17/1/2 ''Population Bottlenecks and Pleistocene Human Evolution'']".) ==Examples in the animal world== {| style="float:right; border:1px solid;" cellspacing=2 cellpadding=2 |- |Year||Estimated bison
population size |- |Before 1492 |align="right"| 60,000,000 |- |1890 |align="right"| 750 |- |2000 |align="right"| 3,600 |} Wisent, also called European bison, faced extinction in the early 20th century. The 3600 animals living in 2000 are all descended from 12 individuals and only two distinct Y chromosomes are left in the species. The population of American Bison fell due to overhunting, nearly leading to extinction around the year 1890 and has since begun to recover. A classic example of a population bottleneck is that of the northern elephant seals, whose population fell to about 30 in the 1890's although it now numbers in the tens of thousands. Also, all existing cheetahs are extremely close genetically suggesting an extreme population bottleneck in the past. Another largely bottlenecked species is the Golden hamster, for which the vast majority are descended from a single litter found in the Syrian desert around 1930. Sometimes further deductions can be inferred from an observed population bottleneck. Among the Galapagos archipelago's giant tortoises (themselves a prime example of a founder effect), the comparatively large population on the slopes of Alcedo volcano is significantly less diverse than four other tortoise populations on the same island. Researchers' DNA analysis dates the bottleneck around 88,000 years before present (YBP), according to a notice in ''Science,'' October 3, 2003. About 100,000 YBP the volcano erupted violently, burying much of the tortoise habitat deep in pumice and ash. The coincidence is suggestive. ==See also== *Small population size * effective population size *Founder effect *Overpopulation *Ice age *Black Death *AIDS *Toba catastrophe theory ==External links== * http://www.sciencedaily.com/releases/2000/01/000110142554.htm *[http://www.sealexperience.com/docs/protect.htm Northern elephant seals] *http://essp.csumb.edu/eseal/kristi_west/history.html Population genetics Human evolution
Population bottleneck
From the article: :All species being survivors in relation to the levels their environment support, there is reasonable thinking that says human beings are due for another bottleneck sometime soon. Really? Please provide cites that this thinking is mainstream. --------------------- Also, AIDS, whilst a disastrous pandemic, is not anywhere near the level needed for a bottleneck. :Not globally, but it is approaching (and projected to reach) that level in parts of Africa. (The Black Death was only a regional phenomenon, too.) User:Mkweise ---- "From a bunch to a bushel" sounds poetic, but I think will lose some readers (even some fluent in English) -- can someone find a better way to say this? User:Slrubenstein :I think a loss of at least 50% qualifies, but I'm not sure. If anyone knows better, please fix the article. User:Mkweise 01:23 23 May 2003 (UTC) What is "ybp"? Uncommon abbreviations should either be spelled out in full the first time they are used in an article, or they should be linked to a glossary entry. :"Years before present" should be spelled out in full at the first encounter.--User:Wetman 12:52, 12 Mar 2005 (UTC) ----- ''"as the rate of drift is inversely proportional to the population size."'' No, the rate of drift is a constant. This needs rethinking as well as rephrasing. --User:Wetman 12:52, 12 Mar 2005 (UTC)
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