Changes

===Population Bottleneck===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 was the key even 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 ago or more. <ref>For more on the recent debate, see: Lane, C.S., Chorn, B.T. & Johnson, T.C. (2013) Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka. <i>Proceedings of the National Academy of Sciences.</i> [Online] 110 (20), 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 population began to influence the genetic makeup of many other subsequent human populations.<ref>For more on population bottleneck events that may have shaped how human genetics evolved, see: Cochran, G. & Harpending, H. (2009) <i>The 10,000 -year explosion: how civilization accelerated human evolution.</i> New York, Basic Books.</ref>

Where there is greater diversity, it is found in Africa itself, where different modern African populations show far greater genetic diversity than the rest of modern human populations in all other regions of the globe. Human Humans in general are much less genetically diverse than many other types of animals. Overall, this lack of diversity has suggested a limited number of humans may have been responsible for the variety of populations today, suggesting relatively small numbers, or even population bottlenecks, shaped the population of areas outside of Africa. The relatively greater genetic diversity in Africa suggests humans were evolving like many other species in Africa, creating new populations over time. Climatic effects or crises may have then triggered a large-scale migration out of Africa that subsequently led to the 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 Genomics and Human Genetics.</i> [Online] 9 (1), 403–433.</ref>

===Migration From Africa===

===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 300,000-200,000 years ago, suggesting that the ancestor to all males derived during the very early evolution of modern humans rather 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 ago or perhaps more similar in time to genetic Adam. There were likely many female genetic lines but Mitochondrial Eve likely became the only female line that survived. All of these early dates suggest greater human diversity and variation were originating and developing in Africa for 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>

For perhaps the first 100As stated,000 years or more, genetic variation was developing as for most human populations largely migrated within Africa , the vast majority of it can be traced to a large wave of migrations that occurred between 300,00080-200,000 50 thousand years ago. Anatomically modern Overall, humans derived from these <i>Homo sapiens</i> species, although by then are about 99.5% similar to each other similar species, such as Neanderthals, had existed. Genetically, Y-chromosomal Adam, or suggesting that relatively few populations have influenced the vast majority of our genetic ancestor for all living men today (i.emakeup.In Africa, although this does not mean he was using linguistic and genetic Adam was the only man around)evidence, seems there were likely about 14 main population groups. These groups show a wider range of genetic variability due to derive between 300,000-founder effects and isolation of very early humans that evolved over 200,000 years ago, suggesting that the ancestor to all males derived during the very early evolution of modern humans rather than within a much later sub-population(Figure 2). Central to Western Modern African populations in eastern 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 120Namibia and South Africa,000 years ago. There were are likely many female genetic lines but Mitochondrial Eve likely became the only female line. All of these early dates suggest greater human diversity and variation were originating in Africa, long before migrations began most similar to significantly shape subsequent other human populations found in other parts of the Earthworld, which suggests that it was this region that modern humans began the large, second wave migration that eventually colonized the rest of the planet. <ref>For more on genetic Adam and Evethe great migration that have subsequently influenced human populations, see: CallawayYotova, V., Lefebvre, J.-F., Moreau, C., Gbeha, E., et al. (20132011) Genetic Adam and Eve did not live too far apart in timeAn X-Linked Haplotype of Neandertal Origin Is Present Among All Non-African Populations. <i>Nature.Molecular Biology and Evolution</i> . [Online] 28 (7), 1957–1962. Available from: doi:10.10381093/molbev/nature.2013.13478 [Accessed: 12 June 2017]msr024.</ref>

As stated, for most human populationsDivergence in genetics began to accelerate again at about 40, the vast majority of it can be traced to a large wave of migrations that occurred between 80-50 thousand 000 years ago. Overall, humans are about 99.5% similar by which time European and Asian populations began to each otherdiverge as human populations migrated into different parts of Eurasia, suggesting that relatively few where the Middle East and Central Asia became an area where human populations have influenced the vast majority of our genetic makeupdiverged from. In Africa, using linguistic and genetic evidencesoutheast Asia, there were likely about 14 main population groups. These groups show a wider range of genetic variability than many other populations throughout the EarthDenisova hominin, which suggests an early hominid that shares an ancestor with Neanderthals, may have also bred with early modern humans spent a lot of time , similar to Neanderthals in Africa before they successfully spread Europe and colonized the remaining other parts of Earth (Figure 2)Asia. Modern African This could explain why up to 4-6% of southeast Asian populations in eastern Africa, between Namibia and South Africa, are likely the most similar to ' genetic makeup shows variation from other human populations. Additionally, which suggests that it was this region that modern humans began the sub-Sahara African populations not only show largevariation, second wave migration(s) that eventually colonized the rest but their genetic makeup lacks any genetic input from Neanderthals, suggesting Neanderthals never migrated to areas south of the planetSahara.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 the great post-Africa migration that have subsequently influenced human populationsgenetic divergence, see: Yotova, V., Lefebvre, J.-F., MoreauBarbujani, CG.& Bertorelle, Gbeha, E., et alG. (20112001) An X-Linked Haplotype Genetics and the population history of Neandertal Origin Is Present Among All Non-African PopulationsEurope. <i>Molecular Biology and EvolutionProceedings of the National Academy of Sciences.</i>. [Online] 28 98 (71), 1957–196222–25. Available from: doi:10.10931073/molbev/msr024pnas.98.1.22.</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. In southeast Asia, 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.<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}}