Changes

===Population Bottleneck===Between Population bottlenecks often reduce genetic diversity, as a large reduction in population means that subsequent populations will inherit that more limited gene pool. Although modern humans evolved perhaps more than 200,000 years ago, as late as between 80,000-70,000 years ago, a population bottleneck has been proposed for modern humans. There is evidence of major climatic change at around this time, perhaps triggered by a super volcanic eruption activity in Lake Toba, Indonesia, that led to rapid global cooling. Some have suggested that this led to a diminished modern human population, resulting was the key event that resulted in a more limited gene pool for modern humans. Others have disputed this finding, and have suggested that the bottleneck may have been triggered much earlier, at about 100,000 years agoor more. In effect<ref>For more on the recent debate, see: Lane, what results do show is that the genetic diversity is relatively limited for many modern human populationsC.S., Chorn, B.T. Where there is greater diversity is found in Africa itself& Johnson, where different modern African populations show far greater genetic diversity than T.C. (2013) Ash from the rest of modern human populations Toba supereruption in Lake Malawi shows no volcanic winter in all other regions East Africa at 75 ka. <i>Proceedings of the globe. Human in general are much less genetically diverse than many other types National Academy of animalsSciences. Overall</i> [Online] 110 (20), this lack of diversity 8025–8029. Available from: doi:10.1073/pnas.1301474110.</ref> Other work has suggested perhaps by 100,000 years ago variations in modern humans became less, as a limited number of humans may have been responsible for population began to influence the variety genetic makeup of populations today. The relatively greater genetic diversity in Africa suggests humans were evolving like many other species in Africa, creating new subsequent human populations over time. Climatic effects or crises <ref>For more on population bottleneck events that may have then triggered a largeshaped how human genetics evolved, see: Cochran, G. & Harpending, H. (2009) <i>The 10,000-scale migration out of Africa that subsequently led to the more narrow genetic diversity found today in other regionsyear explosion: how civilization accelerated human evolution.</i> New York, Basic Books.</ref>

==Migration From Africa==Scientists do not completely agree on all the genetic and archaeological dataWhere there is greater diversity, but there may have been two main migrations from Africa (Figure 1). The first may have been relatively small and it may have occurred more than 140,000 years ago. This migration could have resulted is found in population spreading to West and East AsiaAfrica itself, as where different modern African populations show far as Indonesia. However, greater genetic diversity than the second main migration, between 80,000-50,000 years ago, seems to have been far more significant. In fact, nearly 98% rest of modern human genetics found populations in all other regions of the globe. Humans in general are much less genetically diverse than many global populations appear to trace their genetics to this second migrationother types of animals. In effectOverall, this might have meant that the first migration lack of diversity has suggested a limited number of humans may not have been successful responsible for the variety of populations today, suggesting relatively small numbers, or it resulted in a more limited even population bottlenecks, shaped the population in different regions of areas outside of Africa. The second migrationrelatively greater genetic diversity in Africa suggests humans were evolving like many other species in Africa, which could creating new populations over time. Climatic effects or crises may have consisted of subthen triggered a large-scale migration over out of Africa that subsequently led to the span more narrow genetic diversity found today in other regions.<ref>For more on African genetic diversity, see: Campbell, M.C. & Tishkoff, S.A. (2008) African Genetic Diversity: Implications for Human Demographic History, Modern Human Origins, and Complex Disease Mapping. <i>Annual Review of timeGenomics and Human Genetics.</i> [Online] 9 (1), seemed to spread far and more rapidly across the globe403–433. </ref>

Cro-Magnon are generally considered ===Migration From Africa===Scientists do not completely agree on all the genetic and archaeological data, but there may have been two main migrations from Africa (Figure 1). The first anatomically modern humans in Europe at about 50may have been relatively small and it may have occurred more than 140,000 years ago. Already nearly 1 million years ago, the earliest <i>Homo</i> species had migrated This migration could have resulted in population spreading to Europe, likely via Eurasia. As modern humans expanded in Europe West and East Asia, they increasingly came across Neanderthalsas far as Indonesia. At this pointHowever, the second main migration, between 80,000-50, humans were most likely competing with Neanderthals for resources and food. At times000 years ago, the two species were similar enough seems to breedhave been far more significant. In fact, which has resulted nearly 98% of human genetics found in some genetic makeup of modern humans have Neanderthals DNA (some many global populations range in having 1% appear to trace their genetics to 4% influence in DNA from Neanderthals)this second migration. In effect, but this seems to might have meant that the first migration may not have been relatively successful or it resulted in a more limitedpopulation in different regions outside of Africa. By 20The second migration,000 years agowhich could have consisted of several sub-migrations over the span of time, seemed to spread far and more rapidly across the globe.<ref>For more on the main migrations out of Africa, see: Hans-Jürgen Bandelt, Vincent Macaulay, & Martin Richards (eds.) (2006) <i>Human mitochondrial DNA and the evolution of homo sapiens.</i> Nucleic acids and molecular biology 18. Berlin ; New York, Springer, Neanderthals had disappearedpg. 235. </ref>

In east AsiaDuring this last great wave from Africa, east Siberia, Korea, and Japan may have been reached by 35,000 years ago by it is during this time we see the rapid spread of modern humanson the Earth. This population that migrated to this region also led to a subCro-population that became Magnon are generally considered the first colonizers of the Americas. It is not clear when, but between 40anatomically modern humans in Europe at about 50,000-16,500 years ago. Already nearly 1 million years ago, modern human the earliest <i>Homo</i> species had migrated over the Beringia land bridgeto Europe, likely using the ice sheets that formed via Eurasia. As modern humans expanded in the late glacial maximum period when ice sheets Europe and Asia, they increasingly came across Neanderthals. At this point, humans were most likely competing with Neanderthals for resources and glaciers covered many parts of North Americafood. Recent At times, the two species were similar enough to breed, which has resulted in some genetic work has shown that human makeup of modern humans having Neanderthal DNA (some populations range in the Amazon are genetically similar having 1% to Australoid populations4% influence in DNA from Neanderthals), or populations that also migrated but this seems to east Asia and Australiahave been relatively limited. By 30,000 years ago, Neanderthals had largely disappeared as a distinct sub-species of humans.<ref>For more on migration into Eurasia, see: Semino, O. (2000) The Genetic Legacy of Paleolithic Homo sapiens sapiens in Extant Europeans: A Y Chromosome Perspective. In effect<i>Science</i> [Online] 290 (5494), human migrations to the Americas likely traveled along the coastal regions between North and South America1155–1159. Available from: doi:10.1126/science.290.5494.1155.</ref>

[[FileIn east Asia, east Siberia, Korea, and Japan, modern humans may have been reached these areas by 35,000 years ago. This population that migrated to these regions also led to a sub-population that became the first colonizers of the Americas. It is not clear when, but between 40,000-16,500 years ago, modern humans migrated over the Beringia land bridge, connecting North America with East Asia in Russia and Alaska today, likely using the ice sheets that formed in the late glacial maximum period when ice sheets and glaciers covered many parts of North America. Recent genetic work has shown that human populations in the Amazon are genetically similar to Australoid populations, or populations that also migrated to east Asia and Australia. In effect, human migrations to the Americas likely traveled along the coastal regions between North and South America.<ref>For more on migrations in east Asia, see:Spreading homo sapiens laSu, B., Xiao, J., Underhill, P., Deka, R.svg, et al.png|thumbnail|Figure 1(1999) Y-Chromosome Evidence for a Northward Migration of Modern Humans into Eastern Asia during the Last Ice Age. Proposed migration patterns out <i>The American Journal of Africa Human Genetics.</i> [Online] 65 (6), 1718–1724.; for modern humansmigrations in the Americas, see: Hey, J. (2005) On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas Andy G. Clark (ed.). <i>PLoS Biology.</i> [Online]]3 (6), e193. Available from: doi:10.1371/journal.pbio.0030193.</ref>

===Genetic Diversity===[[File:World Map of Y-DNA Haplogroups.png|thumbnail|left|350px|Figure 2. Map of Y-DNA Haplogroups and the origin of genetic Adam.]]For perhaps the first 100,000 years or more, genetic variation was developing as human populations largely migrated within Africa between 300,000-200,000 years ago. Anatomically modern humans derived from these <i>Homo sapiens</i> species, although by then other similar sub-species, such as Neanderthals, had existed. Genetically, Y-chromosomal Adam, or the genetic ancestor for all living men today (i.e., although this does not mean he was genetic Adam was the only man around), seems to derive between 300,000-200 thousand ,000 years ago, suggesting that the ancestor to all males derived during the very early evolution of modern humansrather than within a much later sub-population. Central to Western Africa seem to be the regions where this early human ancestor influenced subsequent populations. For genetic Eve, or the most recent common matrilineal ancestor Mitochondrial DNA for all humans, is harder to specify, where the dates can range between more than 120,000 years agoor perhaps more similar in time to genetic Adam. There were likely many female genetic lines but Mitochondrial Eve likely became the only female linethat survived. All of these early dates suggest greater human diversity and variation were originating and developing in Africafor the first 100,000 years or more of modern humans, long before migrations began to significantly shape subsequent human populations in other parts of the Earth.<ref>For more on genetic Adam and Eve, see: Callaway, E. (2013) Genetic Adam and Eve did not live too far apart in time. <i>Nature.</i> [Online] Available from: doi:10.1038/nature.2013.13478 [Accessed: 12 June 2017].</ref>

As stated, for most human populations, the vast majority of it can be traced to a large wave of migrations that occurred between 80-50 thousand years ago. Overall, humans are about 99.5% similar to each other, suggesting that relatively few populations have influenced the vast majority of our genetic makeup. In Africa, using linguistic and genetic evidence, there were likely about 14 main population groups. These groups show a wider range of genetic variability than many other populations throughout the Earth, which suggests that humans spent a lot of time in Africa before they successfully spread due to founder effects and colonized the remaining parts isolation of Earth very early humans that evolved over 200,000 years ago (Figure 2). Modern African populations in eastern Africa, between Namibia and South Africa, are likely the most similar to other human populationsfound in other parts of the world, which suggests that it was this region that modern humans began the large, second wave migration(s) that eventually colonized the rest of the planet. <ref>For more on the great migration that have subsequently influenced human populations, see: Yotova, V., Lefebvre, J.-F., Moreau, C., Gbeha, E., et al. (2011) An X-Linked Haplotype of Neandertal Origin Is Present Among All Non-African Populations. <i>Molecular Biology and Evolution</i>. [Online] 28 (7), 1957–1962. Available from: doi:10.1093/molbev/msr024.</ref>

Divergence in genetics began to accelerate again at about 40,000 years ago, by which time European and Asian populations began to diverge as human populations migrated into different parts of Eurasia, where the Middle East and Central Asia became an area where human populations diverged from. In southeast Asia, the Denisova hominin, an early hominid that shares an ancestor with Neanderthals, may have also bred with early modern humans, similar to Neanderthals in Europe and other parts of Asia. This could explain why up to 4-6% of southeast Asian populations' genetic makeup shows variation from other populations. Additionally, sub-Sahara African populations not only show large variation, but their genetic makeup lacks any genetic input from Neanderthals, suggesting Neanderthals never migrated to areas south of the Sahara.On the other hand, Central Asian, European, and Middle Eastern populations do show input from Neanderthals, altough not at very high rates<ref>For more on post-Africa migration genetic divergence, see: Barbujani, G. & Bertorelle, G. (2001) Genetics and the population history of Europe. <i>Proceedings of the National Academy of Sciences.</i> [Online] 98 (1), 22–25. Available from: doi:10.1073/pnas.98.1.22.</ref>

 [[File:World Map of Y-DNA Haplogroups.png|thumbnail|Figure 2. Map of Y-DNA Haplogroups and the origin of genetic Adam.]] ===Summary===Genetic variation among modern humans is relatively limited to most species found on Earth. Populations within Africa were often isolated, developing more diverse genetic variation over time. Once populations left Africa, that diversity began to diminish. Despite physical traits that show variety among humans today in wide regions, the fact is most of those populations show very similar genetic makeup with some input from much older Hominid hominid populations and some early modern humans who migrated before the great migration that occurred between 80-50 thousand years ago. There seems to have been a In effect, since about 80,000 years ago, humans became far more mobile, whereas migration was very limited perhaps for more than 100,000 years in the evolution of <i>Homo sapiens</i>. The next great split divergence between migratory human populations by occurred at about 40,000 years ago, where part of the populations migrated towards Europe and the other part into east Asia and eventually North and South America.{{Mediawiki:Food History}}===References===<references/>[[Category:Wikis]][[Category:Chinese History]] [[Category:European History]][[Category:Middle East History]][[Category:Asian History]][[Category:Medical History]]{{Contributors}}