Post by Noah on Aug 14, 2011 16:20:54 GMT -5
The Duffy antigen system is a genetic factor often used to ascertain whether or not a given population is predominantly of Black African descent. People who possess the antigen are often very susceptible to a form of malaria called P.vivax, whereas those who don't are much less so.
Non-Negroid people thus have one thing in common, and that's that they are just about all Duffy positive. That includes the Hamitic peoples in the Horn and North Africa. Unmixed Negroid populations, on the other hand, are almost entirely Duffy negative.
Note that some African Americans and other New World blacks today -- unlike just about all of their Black African relatives -- are Duffy positive. And they are Duffy positive exclusively due to admixture with Europeans (who, like all non-Negroid populations, are entirely Duffy positive). This is why the percentage of Duffy positive African Americans so closely matches the percentage of African Americans who have a substantial Eurasian component i.e. Eurasians are who they acquired the trait from to begin with:
In fact, even a few members of Bantu/Nilotic populations in South East Africa are Duffy positive. But, as with African Americans, this is almost always due to admixture with non-Negroid peoples and the frequency is thus also quite low. In the case of Kenyan Bantus and Nilotes, it's due to genetic contributions from their Hamitic neighbors to the north in the Horn:
The Hamitic peoples of the Horn, on the other hand, are almost entirely Duffy positive, just like other non-Negroid populations. And they didn't require admixture with Eurasians to get that way either. They got that way through common descent with Eurasian populations (as the abundant Eurasian mtDNA haplogroups and autosomal DNA in the Horn region, among other things, testify). Only in areas of the Horn where admixture with Negroid peoples is substantial this doesn't happen to be the case.
For example, a study conducted on various Hamito-Semitic populations in Ethiopia (Oromo, Amhara, Tigre, etc.) found an incidence of 70% Duffy positivity in the malarious community in the southwestern town of Gambela, where some of the Hamitic peoples there had interbred with neighboring Nilotic people. On the other hand, 98% of the Hamitic peoples tested in Addis Ababa, Ethiopia's capital, were Duffy positive since less admixture with Black Africans (who are mostly Duffy negative) had taken place there:
Non-Negroid people thus have one thing in common, and that's that they are just about all Duffy positive. That includes the Hamitic peoples in the Horn and North Africa. Unmixed Negroid populations, on the other hand, are almost entirely Duffy negative.
"P. vivax was endemic in North Africa until many countries launched eradication programs and remains endemic in the Afro-Asiatic populations of Sudan, Somalia and Ethiopia; in these places, where testing has been done, populations have predominantly been Duffy positive"
www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W7G-4N7YGND-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=2c549cf4f7a5e4669336184ad70114de
"Black Africans are Duffy-negative and are thus resistant to P. vivax infection."
books.google.ca/books?id=1Zl70SLDU3oC&pg=PA493#v=onepage&q&f=false
"The best measure of "whiteness" is the presence of positive Duffy blood proteins[...] Members of the White race always possess a positive phenotype for Duffy red blood cell antigens and African Blacks have only a small positive rate; thus determination of the phenotype in American Blacks permits an estimation of the degree of genetic admixture which has occurred in a particular Black population."
ajph.aphapublications.org/cgi/reprint/75/5/558.pdf
Note that some African Americans and other New World blacks today -- unlike just about all of their Black African relatives -- are Duffy positive. And they are Duffy positive exclusively due to admixture with Europeans (who, like all non-Negroid populations, are entirely Duffy positive). This is why the percentage of Duffy positive African Americans so closely matches the percentage of African Americans who have a substantial Eurasian component i.e. Eurasians are who they acquired the trait from to begin with:
"Approximately 30% of African-American's erythrocytes are Duffy positive as a result of Caucasian admixture"
books.google.ca/books?id=_eXYwH13jckC&pg=PA111&lpg=PA111&dq=%22are+Duffy+positive%22&source=bl&ots=hqHWIzgk5G&sig=9fm_qagTUBg12wEAsXQHFV8pebg&hl=en&ei=a9faSqCPCtDX8Ab3o4m3BQ&sa=X&oi=book_result&ct=result&resnum=9&ved=0CCIQ6AEwCA#v=onepage&q=%22are%20Duffy%20positive%22&f=false
In fact, even a few members of Bantu/Nilotic populations in South East Africa are Duffy positive. But, as with African Americans, this is almost always due to admixture with non-Negroid peoples and the frequency is thus also quite low. In the case of Kenyan Bantus and Nilotes, it's due to genetic contributions from their Hamitic neighbors to the north in the Horn:
"Occasional reports of P. vivax in Kenya have commonly been ascribed, a priori, either to confusion with the morphologically similar P. ovale or to the genetic contribution from Hamitic or other populations who are largely Duffy positive."
www.ajtmh.org/cgi/content/full/75/4/575
The Hamitic peoples of the Horn, on the other hand, are almost entirely Duffy positive, just like other non-Negroid populations. And they didn't require admixture with Eurasians to get that way either. They got that way through common descent with Eurasian populations (as the abundant Eurasian mtDNA haplogroups and autosomal DNA in the Horn region, among other things, testify). Only in areas of the Horn where admixture with Negroid peoples is substantial this doesn't happen to be the case.
For example, a study conducted on various Hamito-Semitic populations in Ethiopia (Oromo, Amhara, Tigre, etc.) found an incidence of 70% Duffy positivity in the malarious community in the southwestern town of Gambela, where some of the Hamitic peoples there had interbred with neighboring Nilotic people. On the other hand, 98% of the Hamitic peoples tested in Addis Ababa, Ethiopia's capital, were Duffy positive since less admixture with Black Africans (who are mostly Duffy negative) had taken place there:
"The Duffy blood group determinants have been identified by Miller and associates as possible mediators on erythrocytes for the invasion of Plasmodium vivax merozoites. Accordingly, Duffy-positive persons would be susceptible to patent infection with P. vivax and Duffy-negative persons would be insusceptible to such infection. This hypothesis has been offered as an explanation for the widespread refractoriness to vivax malaria among West Africans and their descendants in the New World, most of whom are Duffy negative. By contrast, virtually all people of European and Asian descent are Duffy-positive. Support for the hypothesis has been provided by the results of field studies conducted in West Africa and in Central America. The relationship between vivax malaria and the Duffy factor in eastern Africa has not, to our knowledge, been investigated. People representing two ethnic groups and residing in the same town in Ethiopia were shown by Armstrong to have significantly different rates of infection with P. vivax. The present study was designed to examine the Duffy-vivax relationship as a possible explanation for this difference, and to determine the applicability of the aforementioned hypothesis to people of eastern Africa[...] We investigated an hypothesis relating the Duffy-negative blood type with in susceptibility to vivax malaria and previously associated only with people of West African ancestry in three population samples of eastern African stock. The samples included Nilotic and Hamitic-Semitic residents of a malarious locale in Ethiopia and Hamito-Semites in Addis Ababa where malaria is not endemic. Fresh red blood cells from 191 subjects were tested with Duffy antisera, anti-Fya and anti-Fyb. Duffy-positive rates in the malarious community were 8% for the Nilotes and 70% for the Hamito-Semites; the Hamito Semites in Addis Ababa were 98% Duffy-positive. The relative prevalences of Plasmodium vivax in the two study groups at risk to malaria were 2.4% for the Nilotes and 27.3% for the Hamito-Semites, producing a ratio similar to the ratio of Duffy-positives in the two samples. We interpret the data as supportive of the Duffy-vivax hypothesis with reference to a part of eastern Africa, and we suggest that the Duffy-negative genotype may represent the original, rather than the mutant, condition in tropical Africa."
www.ajtmh.org/content/30/2/299.citation