Study Links Africans’ Ability to Digest Milk to Spread of Cattle Raising

Medical Xpress, March 13, 2014

Babies are born with the ability to digest lactose, the sugar found in milk, but most humans lose this ability after infancy because of declining levels of the lactose-digesting enzyme lactase. People who maintain high levels of lactase reap the nutritive benefits of milk, however, offering a potential evolutionary advantage to lactase persistence, or what is commonly known as lactose tolerance.

A new study led by University of Pennsylvania researchers—constituting the largest investigation ever of lactase persistence in geographically diverse populations of Africans—investigated the genetic origins of this trait and offers support to the idea that the ability to digest milk was a powerful selective force in a variety of African populations which raised cattle and consumed the animals’ fresh milk.

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The paper will be published March 13 in the American Journal of Human Genetics.

Previous research had shown that northern Europeans and people with northern European ancestry, as well as populations from Africa, the Arabian Peninsula and Central Asia with a tradition of fresh milk production and consumption, continue to express the lactase enzyme into adulthood. Some of these earlier studies had traced the genetic origin of this trait in Europeans to a particular mutation that regulates the expression of the gene that codes for lactase. And in 2007 a study by Tishkoff, Ranciaro and colleagues examined African populations and found three addition genetic variants associated with lactase persistence that had not been previously identified.

“But these variants didn’t completely account for the reason why some Africans were able to digest milk,” Ranciaro said.

To try to reconcile these apparent discrepancies between genotype, the genetic basis of a characteristic, and phenotype, the characteristic itself, Ranciaro, along with colleagues, led field studies to often-remote areas of Kenya, Tanzania and Sudan to collect blood samples and perform a lactose tolerance test on people from diverse ethnic backgrounds.

“The idea was that we wanted to sample as many populations, and as diverse a set of populations, as possible,” Ranciaro said. “We included pastoralists, agro-pastoralists, agriculturalists and hunter-gatherers, so the four major subsistence patterns were all covered.”

The Penn researchers worked with African collaborators and local district offices and tribal chiefs to spread the word and recruit volunteers for their study.

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To look for genetic variations among the populations’ abilities to digest milk, the team sequenced three genomic regions thought to influence the activity of the lactase-encoding LCT gene in 819 Africans from 63 different populations and 154 non-Africans from nine different populations in Europe, the Middle East and Central and East Asia.

They also examined the results of the lactose tolerance test in 513 people from 50 populations in East Africa.

Their sequencing and phenotyping efforts confirmed the association between lactase persistence and three known single–nucleotide polymorphisms, or SNPs, places where the DNA sequence varies in just one “letter.” But they also identified two new SNPs associated with the trait located in regions that are thought to regulate lactase gene expression.

Their analysis revealed strong evidence of recent positive selection affecting several variants associated with lactase persistence in African populations, likely in response to the cultural development of pastoralism. The distinct geographic patterns in which these variants were present correlate in many cases with historic human migrations, mixing between populations as well as the spread of cattle, camels or sheep.

For example, they found the variant associated with lactase persistence in Europeans, T-13910, in central and northern African pastoralist groups, suggesting that these groups may have mixed historically with a non-African population. The age of this genetic mutation is estimated to be 5,000-12,300 years old, coinciding with the origins of cattle domestication in North Africa and the Middle East. And a variant, G-13915, found at high frequencies in the Arabian Peninsula, and also present in northern Kenya and northern Sudan, dates to roughly 5,000 years ago, around the time that archaeological evidence suggests that camels were domesticated in the region.

Another variant, G-13907, was identified in the northern reaches of Sudan and Kenya as well as in Ethiopia. The researchers speculate that the mutation may have arisen in Cushitic populations in Ethiopia, who later migrated into Kenya and Sudan in the last 5,000 years.

They observed still another variant, C-14010, in Tanzania and Kenya as well as in southern Africa. This variant is believed to have arisen 3,000 to 7,000 years ago, a timing in line with the migration of pastoralists from North Africa into East Africa. The researchers’ analysis suggests that this variant spread more recently into southern African, perhaps only in the last 1,000 years.

“We’re starting to paint a picture of convergent evolution,” Tishkoff said. “Our results are showing different mutations arising in different places that are under selection and rising to high frequencies and then reintroduced by migration to new areas and new populations.”

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  • D.B. Cooper

    It’s considered a favorable gene, and as far as I know, a lot of the human race throughout the cosmos are able to digest dairy products just fine.

    I hope, I really, really, do hope these University of Pennsylvania researchers (students in their 20s?) took into consideration that humans throughout Earth also consumed dairy products from sources other than bovine in origin. Goats’ milk comes to mind.
    I also recall watching a program explaining how the Swiss became such experts at cheese making. Their climate was cool enough to allow cheese to stay fresh for weeks at a time, which was useful back in the old days.

    • JohnEngelsman

      Interesting, but not important. If milk were truly important, then Asians would have developed a gene to allow them to easily digest milk into adulthood.

      • D.B. Cooper

        Even most Asians are able to consume dairy products just fine. In fact, I’ve seen them go all out on ice cream, extra cheese on pizza, giant milkshakes, etc.

        • Martel

          Its about the ability to digest the products not the ability to be free from any side effects. Europeans have a stronger reaction to lactose products if they lack the tolerance, other peoples simply flush it through their system, the physical reaction is hardly noticeable.

      • APaige

        John,
        Just because Asians did not develop a gene does not mean its not important. How many milk bearing animals fit for humans are in Asia? Do you actually believe Asians have a superpower that is something was important they would develop it? Well they sure could not “invent” it. If the world only relied on Asians to develop something important the most advanced technological tool would be the compass.

        • Martel

          The word ‘superpower’ popped into my head when reading his comment as well. I never met a man who literally fantasizes about the capabilities of another race like this guy.

          Its odd and creepy at times.

      • Martel

        From an evolutionary standpoint this comment doesn’t make any sense, a gene is not ‘developed’ just because something is ‘important enough’. Just stick to randomly posting the same IQ scores over and over again.

        • JohnEngelman

          Read his nickname. JohnEngelsman is not me.

          Mutations happen randomly. If they are useful they tend to spread.

          • Martel

            That’s funny, it will be difficult to tell you both apart. Fortunately you are not stuck in Lamarckian days. I had not noticed this imposter before.

          • MBlanc46

            AmRen ought to delete that bogus account.

          • JohnEngelman

            They probably will. Meanwhile he is good for a few laughs.

    • Stammon

      Caesar’s men made him ice cream in the African desert.

  • Martel

    The mutation for tolerating products containing lactose in Northern India is similar to the mutation in Europe.

  • dd121

    Europeans lived in hovels with their animals for thousands of years. The cows produced milk in the winter which kept them alive. Those that couldn’t tolerate that, and died, did not pass on their genes.

  • 1stworlder

    There is a reason why the Queen of England drinks raw milk and the leftists in CA try to stop its sale. Black and brown tend to be lactose intolerant. That heifer international charity was poorly thought out.

  • Rhialto

    This is not a significant fact for race realists, except as one more example of how different groups of humans adapted to different niches in different environments. In societies where milk is useful as an adult food, there was a selective advantage in retaining the capability of digesting lactose past infancy. Just as in a niche wherein long range planning was useless, there is no selective advantage in developing or retaining this capability. In fact, it may be a disadvantage, as brain tissue is expensive.