Geography, Race and Genetics

There are several methods used to model human genetic variation. Genetic distance is a measure used to quantify the genetic differences between two populations. It is based on the principle that two populations that share similar frequencies of a trait are more closely related than populations that have more divergent frequencies of a trait. In its simplest form it is the difference in frequencies of a particular trait between two populations. For example the frequency of RH negative individuals is 50.4% among Basques, is 41.2% in France and 41.1 in England. Thus the genetic difference between the Basques and French is 9.2% and the genetic difference between the French and the English is 0.1%for the RH negative trait.

When only one trait is considered it often results in two very distant populations having little or no genetic difference. For example the frequency of blood group B allele in Russia is the same as in Madagascar indicating zero value for genetic distance. To adjust for these instances it is thus necessary to average values over several genetic systems. As DNA of all humans is 99.9 percent the same the vast majority of traits show little genetic distance between the continents. However, for a the few traits that are highly polymorphic genetic distances can be calculated and used to create phylogenetic relationships.

An Indigenous Australian , Melanesian, African Nilotic with eurasian blood and nom-bantoid and European mongolizated of North Baltic Sea. Though Oceanians resemble Africans they are the most genetically distant. Africans are more closely related to Europeans than any other group despite having different skin colors.

Historically people have chosen spouses from nearby villages. Hence genetic distance is largely related to geographic distance between populations.[6] Genetic distance may also occur due to physical boundaries that restrict gene flow such as Islands cut off by rising seas.

A study by Cavalli-Sforza using 120 blood polymorphisms provides information on genetic distances of the various continents.[7]

The largest genetic distance between any two continents is between Africa and Oceania at 24.7. Based on physical appearance this may be counterintuitive, since Australians and New Guineans resemble Africans with dark skin and sometimes frizzy hair. This resemblance is probably an example convergent evolution. 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 22.6%. This is expected since the longest geographic distance by land is between Africa and South America. The shortest genetic distance at 8.9% is between Asia and the Americas indicating a more recent separation.

Africans are the most divergent continent with all other groups being more related to each other than to Africa. This is expected in accordance with the Recent single-origin hypothesis. The population most closely related to Africans are Europeans. However, this short distance indicates significant interaction and gene exchange between Africa and Europe in the not so distant past. Europe has a genetic variation in general about three times less than that of other continents. Even though Europeans are the non-African group closest to Africans, Europeans are most closely related to East Asians. As the genetic distance from Africa to Europe (16.6) is shorter than the genetic distance from Africa to East Asia (20.6) Cavalli-Sforza proposes that both Asian and African populations contributed to the settlement of Europe which began 40,000 years ago. The overall contributions from Asia and Africa were estimated to be around two-thirds and one-third, respectively. Europe has a genetic variation in general about three times less than that of other continents.

Gene flow between continents

Gene flow is the exchange of genes from one population to another. Gene flow has the effect of reducing the genetic distance between two populations. Since genes are exchanged between neighboring populations many traits are distributed along clines. The boundaries of the major continents may in some cases restrict gene flow, allowing for genetic differentiation.

However many of the political divisions of today are not naturally occurring and in the past have not restricted gene flow. Europe and Asia are in fact the single continent of Eurasia. This would explain the relatively small genetic distance of 9.7% as calculated by Cavalli-Sforza.

Controversially North Africa is sometimes included as Part of Eurasia. Northeast Africa is adjacent to Saudi Arabia and thus Africans have a long history of interaction with the middle east. Populations in the horn of Africa have significant Arab admixture. African mitochondrial DNA haplotypes are also frequent in the Middle east. Across the Sahara from Sudan to Senegal interactions between blacks and Arabs have resulted in significant gene exchange between the populations. 20% of North Africans have sub-saharan African mitochondrial DNA haplogroups. During the 8th century the Moors from North Africa conquered the Iberian peninsula, in the process they would have brought African admixture to Europe. Studies have shown about 4% of the population in Spain and Portugal have sub-Saharan mtDNA haplogroups. This is clinically distributed across Europe from southwest to North east with Northern Europe showing no presence.

Africa is the most genetically divergent continent. However, the most closely related population to Africa based on genetic distance is Europe at 16.6%. This may be counterintuitive based on different skin colors. Independent evolution on the different continents would result in equal genetic distances between Africa and the other continents. However, this low figure of 16.6(relative to Australia 24.7, and America 22.6%) indicates that there has been substantial interaction and exchange of genes between Africa and Europe. Cavalli-Sforza estimates that Europeans are mixed race population, one third African and two thirds Asian. [7]

Joseph Greenberg classified American languages into three large families. He proposed that these families represent three separate migrations that filled the Americas in the order they arrived. These separate migrations across the Bering strait would have continued to bring new genes from Asia thus reducing the genetic distance between Asia and America.

Australasia is largely considered to be the most isolated continent. It was occupied at least 40,000 years ago when sea levels were much lower and the shortest distance between Indonesia and Australia was a 90 km sea voyage. 20,000 years ago at the end of the last Glacial Maximum, sea levels rose due to melting ice sheets flooding much of Australia's coastline and increasing its geographic isolation from Asia. Tasmania was cut off from Australia 10,000 years ago making it the most isolated region. These obstacles significantly restricted gene flow to indigenous Australasians. Second to Africa, Australasia is the most genetically divergent continent by genetic distance; however evidence suggests that even with Australasia gene flow has been taking place. Fossils of the Dingo in Australia have been dated to only 3500 years ago indicating that it was recently introduced. The dingo is native to India. Some Y chromosomal studies indicate a recent influx of y chromosomes from the Indian subcontinent. [12] More recently fisherman from Makassar in Indonesia regularly made contact with Indigenous Australians from possibly as early as 1000 CE.

Human genetic variation is the natural variation in gene frequencies observed between the genomes of individuals or groups of humans. Variation occurs at both the individual level (differences between individual people) and at the geographic level, i.e. differences between groups of people living in different parts of the world (ethnic groups, races).

In genetics there may be multiple variants of any given gene (polymorphism), these are called alleles. Any individual human has only two copies of any given allele, one inherited from their mother and the other from their father, but many more different versions of the gene may exist. Genetic variation is also distributed geographically, the frequency of any given allele may be greater in humans from on geographic region than in humans from some other region.

There are at least two reasons why genetic variation is geographically distributed:

The study of human geographic variation has both evolutionary significance and medical applications. The study can help scientists understand ancient human population migrations as well as how different human groups are biologically related to one another. From a medical perspective the study of human genetic variation may be important because some disease causing alleles occur at a greater frequency in people from specific geographic regions.

Geographic isolation, or allopatry, is a term used in the study of evolution. When part of a population of the same species becomes geographically isolated from the remainder, it may over time evolve characteristics different from the parent population (due to natural selection). This is particularly likely to happen if the isolated population is small, because of founder effects, or if the population become isolated in an environment which makes new demands upon it. Much research has shown that this is a major reason why there are so many different species throughout the world.

If there is sufficient genetic change following geographical isolation, then if the geographical barriers are removed (perhaps due to human activity), members of the two populations will be unable to successfully mate with each other. At this point, a new species has emerged. Geographical isolation is thus a key factor in speciation, the formation of new species - also termed allopatric speciation.

However, it is more common for there to be considerable genetic and phenotypic change without the loss of the capacity for interbreeding - interbreeding is simply prevented by the geographical separation of populations. In this case the populations are normally regarded as subspecies.

The African Elephant for instance has always been regarded as a single species. Because of morphological and DNA differences some scientists classify the elephants into three subspecies. Researchers at the University of California, San Diego (UCSD) have argued that divergence due to geographical isolation has gone further, and the elephants of West Africa should be regarded as a separate species from either the savanna elephants of Central, Eastern and Southern Africa, or the forest elephants of Central Africa.

Other cases arise where two populations that are quite distinct morphologically, and are native to different continents, have been classified as different species; but when members of one species are introduced into the other's range, they are found to interbreed freely, showing that they were in fact only geographically isolated subspecies. This was found to be the case, for example, when the Mallard Anas platyrhynchos was introduced into New Zealand; it interbred freely with the native Grey Duck, which had been classified as a separate species, Anas superciliosa; it is controversial whether its specific status can now be retained.

The investigation of surnames in genetics can be said to go back to George Darwin, a son of Charles Darwin. In 1875, George Darwin used surnames to estimate the frequency of first-cousin marriages and calculated the expected incidence of marriage between people of the same surname (isonymy). He arrived at a figure between 2.25% and 4.5% for cousin-marriage in the population of Great Britain, with the upper classes being on the high end and the general rural population on the low end. (His parents, Charles Darwin and Emma Wedgwood, were first cousins.) This simple study was innovative for its era. The next stimulus toward using genetics to study family history had to wait until the 1990s, when certain locations on the Y chromosome were identified as being useful for tracing male-to-male inheritance.

(George H. Darwin, "Note on the Marriages of First Cousins", Journal of the Statistical Society of London 38:3 (Sep., 1875), pp. 344-348)

Dr. Karl Skorecki, a Canadian nephrologist of Ashkenazi parentage, noticed that a Sephardic fellow-congregant who was a Kohen like himself had completely different physical features. According to Jewish tradition, all Kohanim are descended from the priest Aaron, brother of Moses. Skorecki reasoned that if Kohanim were indeed the descendants of only one man, they should have a common set of genetic markers and should perhaps preserve some family resemblance to each other.

To test that hypothesis, he contacted Professor Michael Hammer of the University of Arizona, a researcher in molecular genetics and pioneer in Y chromosome research. Their report in the Nature in 1997 sent shock waves through the worlds of science and religion. A particular marker was indeed more likely to be present in Jewish men from the priestly tradition than in the general Jewish population. It was apparently true that a common descent had been strictly preserved for thousands of years. (See Y-chromosomal Aaron). Moreover, the data showed that there were very few “non-paternity events”.

The first to test the new methodology in general surname research was Bryan Sykes, a molecular biologist at Oxford University. His study of the Sykes surname obtained valid results by looking at only four markers on the male chromosome. It pointed the way to genetics becoming a valuable assistant in the service of genealogy and history. In 2001, Sykes went on to write the popular book The Seven Daughters of Eve.

In the wake of that book's success, and the growing availability and affordability of genealogical DNA tests, genetic genealogy as a field began growing rapidly. By 2003, the field of DNA testing of surnames was declared officially to have “arrived” in an article by Jobling and Tyler-Smith in Nature Reviews Genetics. The number of firms offering tests, and the number of consumers ordering them, had risen dramatically.

Another milestone in the acceptance of genetic genealogy is the Genographic Project. The Genographic Project is a five-year research partnership launched by the National Geographic Society and IBM in 2005. Although its goals are primarily anthropological, not genealogical, the project's sale of over 225,000 testing kits (as of October 2007) of its public participation kits, which test the general public for either twelve STR markers on the Y chromosome or the HVR1 region of the mtDNA, has helped increase the visibility of genetic genealogy.

More state-of-the-art commercial laboratories nowadays recommend testing at least 25 markers, since the more markers that are tested, the more discriminating and powerful the results will be. A 12 marker STR test is usually not discriminating enough to provide conclusive results for a common surname. Genetic laboratories such as Genebase give the option of testing 44 Y-DNA Markers.[2]

Annual sales of genetic genealogical tests for all companies, including the laboratories that support them, are estimated to be in the area of $60 million (2006).

Since the year 2000, dozens of relevant academic papers have been published, and thousands of private test results organised by surname study groups have been made available on the internet. The comparison of results may be complicated by the fact that some laboratories use different testing methods. Apparently differing results from two sources may in fact be identical, and vice-versa.