|August 30th, 2011||#1|
Bread and Circuses
12 % of the DNA Differs Amongst Human Races and Populations
|November 27th, 2011||#2|
Bread and Circuses
Degree of Genetic Difference between the Races of Humanity
What are the percentages of genetic differences between the human races? Perhaps the best study to date (2010) on this subject is still that of Masatoshi Nei and Arun K. Roychoudhury from Evolutionary Relationships of Human Populations on a Global Scale (1993). The following table (Fig. 1 below) of estimates of genetic differences between human populations is from their study.
The following table of percentages of genetic differences between human populations presents the estimates for 19 populations from the above table in an easier to read and understand format. The human-chimpanzee genetic difference, giving the greatest degree of difference from the commonly accepted range using the same methodology, is added for context and comparison.
If one were to spatially visualize the first column of the above scale, with a German standing at a distance of 20 feet from an Englishman, a Finn would stand at a distance of 50 feet, an Italian at 70 feet, a northern Indian at 200 feet, a Japanese at 610 feet, a North American Amerindian at 760 feet, a Nigerian at 1,330 feet, and a Chimpanzee at 16,000 feet.
The greatest percentage of genetic difference is .176% between Nigerians and Australian Aborigines. This is 11% of the genetic difference of 1.6% between humans and chimpanzees, different biological Families whose ancestral lines are believed to have separated 5-7 million years ago.
The .133% genetic difference between the English and Nigerian populations is 8.3% as large as the genetic difference between humans and chimpanzees.
The .061% genetic difference between the English and Japanese or Korean populations is 3.8% as large as the genetic difference between humans and chimpanzees. Seen in this context, these are very significant genetic differences.
It is also worth noting that for both the English and the Japanese, representing Europeans and Northeast Asians, the greatest percentage of genetic difference is with the Nigerians, and that the degree of this difference, .133% for the English and .149% for the Japanese, is very similar.
By comparison, the English and Japanese degree of difference from the Australian Aborigine population, .122% for the English and .062% for the Japanese, is very different, with the English-Australoid difference twice as great as the Japanese-Australoid difference.
A widely cited 1994 study by Cavalli-Sforza et al. evaluated the genetic distances between 42 native populations from around the world based on 120 blood polymorphisms.
These 42 populations can be grouped into 9 main clusters, which Cavalli-Sforza termed African (sub-Saharan), Caucasoid (European), Caucasoid (extra-European), Northern Mongoloid (excluding Arctic populations), Northeast Asian Arctic, Southern Mongoloid (mainland and insular Southeast Asia), Pacific Islander, New Guinean and Australian, and American (Amerindian).
The largest genetic distance between any two continents is between Africa and Oceania at 0.2470. Based on physical appearance this may be counterintuitive, since Indigenous Australians and New Guineans resemble Africans with dark skin and sometimes frizzy hair.
This large figure for genetic distance reflects the relatively long isolation of Australia and New Guinea since the end of the last glacial maximum when the continent was further isolated from mainland Asia due to rising sea levels.
The next largest genetic distance is between Africa and the Americas at 0.2260. This is expected since the longest geographic distance by land is between Africa and South America.
The shortest genetic distance at 0.0155 is between European Caucasoids and Non-European Caucasoids.
Africa is the most genetically divergent continent, with all other groups being more related to each other than to Sub-Saharan Africans.
Europe has a genetic variation in general about three times less than that of other continents, and the genetic contribution of Asia and Africa to Europe is thought to be 2/3 and 1/3 respectively.
Only force rules. Force is the first law - Adolf H. http://erectuswalksamongst.us/ http://tinyurl.com/cglnpdj Man has become great through struggle - Adolf H. http://tinyurl.com/mo92r4z Strength lies not in defense but in attack - Adolf H.
Last edited by RickHolland; November 27th, 2011 at 02:16 AM.
|November 27th, 2011||#3|
Bread and Circuses
The Human Genome Diversity Project: past, present and future
The Major and Minor Races of Mankind
Genetic variation, classification and 'race'
New genetic data has enabled scientists to re-examine the relationship between human genetic variation and 'race'. We review the results of genetic analyses that show that human genetic variation is geographically structured, in accord with historical patterns of gene flow and genetic drift. Analysis of many loci now yields reasonably accurate estimates of genetic similarity among individuals, rather than populations. Clustering of individuals is correlated with geographic origin or ancestry. These clusters are also correlated with some traditional concepts of race, but the correlations are imperfect because genetic variation tends to be distributed in a continuous, overlapping fashion among populations. Therefore, ancestry, or even race, may in some cases prove useful in the biomedical setting, but direct assessment of disease-related genetic variation will ultimately yield more accurate and beneficial information.
Implications of biogeography of human populations for 'race' and medicine
In this review, we focus on the biogeographical distribution of genetic variation and address whether or not populations cluster according to the popular concept of 'race'. We show that racial classifications are inadequate descriptors of the distribution of genetic variation in our species. Although populations do cluster by broad geographic regions, which generally correspond to socially recognized races, the distribution of genetic variation is quasicontinuous in clinal patterns related to geography.
The broad global pattern reflects the accumulation of genetic drift associated with a recent African origin of modern humans, followed by expansion out of Africa and across the rest of the globe. Because disease genes may be geographically restricted due to mutation, genetic drift, migration and natural selection, knowledge of individual ancestry will be important for biomedical studies. Identifiers based on race will often be insufficient.
The emerging picture is that populations do, generally, cluster by broad geographic regions that correspond with common racial classification (Africa, Europe, Asia, Oceania, Americas). This is not surprising as the distribution of variation seen today is primarily the result of the history of human expansion out of Africa, the pathways of expansion through Eurasia, subsequent demographic expansions of populations into Oceania and the Americas and local and long-range migrations. A general pattern of isolation by distance has allowed drift to accumulate in spite of some damping due to local migrations. The pattern laid down by the initial expansion of modern humans out of Africa is detectable using Y-chromosome, mtDNA and autosomal markers. Selection in response to region-specific factors has enhanced the differences at some loci, and recent migrations and demic expansions have added complexity to the pattern. But 'races' are neither homogeneous nor distinct for most genetic variation.
Understanding the global distribution of genetic variation is biomedically important, but we emphasize that existence of differences, however small, should not be a basis for discrimination. Statements like "We hold these truths to be self-evident, that all men are created equal..." (US Declaration of Independence, 1776) reflect morality, not science. One can accept this moral imperative and still recognize that all individuals, independently conceived, are genetically unique.
Support from the relationship of genetic and geographic distance in human populations for a serial founder effect originating in Africa
Equilibrium models of isolation by distance predict an increase in genetic differentiation with geographic distance. Here we find a linear relationship between genetic and geographic distance in a worldwide sample of human populations, with major deviations from the fitted line explicable by admixture or extreme isolation. A close relationship is shown to exist between the correlation of geographic distance and genetic differentiation (as measured by F ST) and the geographic pattern of heterozygosity across populations. Considering a worldwide set of geographic locations as possible sources of the human expansion, we find that heterozygosities in the globally distributed populations of the data set are best explained by an expansion originating in Africa and that no geographic origin outside of Africa accounts as well for the observed patterns of genetic diversity.
Although the relationship between F ST and geographic distance has been interpreted in the past as the result of an equilibrium model of drift and dispersal, simulation shows that the geographic pattern of heterozygosities in this data set is consistent with a model of a serial founder effect starting at a single origin. Given this serial-founder scenario, the relationship between genetic and geographic distance allows us to derive bounds for the effects of drift and natural selection on human genetic variation.
|November 27th, 2011||#4|
Join Date: Jul 2008
The differences could be less than 1%, and those differences still be more significant than all the similarities combined. If there are racial differences in genes that dictate how the brain develops, for example, it could mean... everything.
No time for the old in 'n out, love. I've just come to read the meter.