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Africans' ability to digest milk linked to spread of cattle raising
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[QUOTE]Originally posted by Amun-Ra The Ultimate: [QB] Here's below a table about lactase persistence frequencies in various African and world populations I posted in the [URL=http://www.egyptsearch.com/forums/ultimatebb.cgi?ubb=get_topic;f=8;t=008330]Green Sahara[/URL] thread. It's important to make the distinction between the phenotype (having Lactase Persistence (LP) in adulthood) and having the genotype for that trait, since all the responsible or associated genes(alleles) for LP have not been found yet. In fact, a great majority of them have not been found yet(at least at the moment of writing this, see new studies). Individuals are classified into 3 types, those with lactase persistence (LP), lactase intermediate persistence (LIP) or lactase non-persistence (LNP). So, imo, for a population to exhibit a high frequency of LP there must be 2 main prerequisites: 1) Practice of herding, in the past. So access to animal milk 2) A strong positive natural selection element. A very high level of lactase persistance in a population can be explained by a strong bottleneck effect in the past of a herding population, which led to the selection of people with LP in a way that people without LP couldn't survive or reproduce much. It's hard to imagine many situations where it would be the case. We're talking, imo, about major bottleneck events like drought, famine, diseases (due to lack of milk vitamins or, if the LP gene is also responsible for other phenotype trait(s), like protection against some infections diseases for example). So ultimately populations with a history of herding have various level of LP depending on degree of adaptive advantage provided by the consumption of milk at a certain point in their past history. The most common gene associated with LP in European population have been identified (T-13910 ). But there's still many people around the world who doesn't have that gene/allele and still possess the LP trait. 3 new genes associated with LP have been identified by Tishkoff and al in Africa, that is, C-14010, G-13915 and G-13907. The C-14010 seems to be associated with Nilo-Saharan and Cushitic people. Still many people in Africa, and the rest of the world, don't possess any of the 4 known associated genes mentioned above (and a few one ones discovered in recent studies) In Africa, populations like Wolof, Yoruba, Igbo(Ibo), Gabon (Bantu), Xhosa have the LP phenotype but not any of the known genes associated with it (genes associated with it in those populations will probably be found in future research). On the table below, we can see for example the LP frequencies such as: Gabon Bantu=40% Nigeria Igbo=18% Nigeria Yoruba=17% Senegal Toucouleurs=90% Senegal Wolof=51% South Africa Sotho=35% South Africa Xhosa=18% The populations cited above have the LP phenotype but the genotype associated with it have not been found yet for the most part. In the majority of the African populations the allele(s) associated or responsible for their LP is either unknown, C-14010 or one of the other 2 identified alleles associated with LP in Africa. New studies can provide updated information on the new genes responsible for the LP phenotype that have been discovered. One of the important point here is that there's many different alleles for LP in the world, some seems to be more prevalent (and probably originated) in Europe/Middle East, others in Africa, etc. The genes responsible for the LP phenotype has not been found yet for many populations in Africa. Here's the table about lactase persistence frequencies, thus LP phenotype, in various African and world populations (a very nice compilation of past studies): [IMG]http://i1274.photobucket.com/albums/y421/amunratheultimate2/Misc/Thelactasepersistencephenotypefrequenciesinworldpopulations_zpscf1bed16.jpg~original[/IMG] From [i]The Evolutionary Role of Human-Specific Genomic Events Yuval Itan (2009) [/i] [/QB][/QUOTE]
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