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Thread: The Evolution of Lactose Tolerance in Dairying Populations

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    The Evolution of Lactose Tolerance in Dairying Populations

    The Evolution of Lactose Tolerance in Dairying Populations

    http://www.oxfordhandbooks.com/view/...199694013-e-12

    "Abstract and Keywords

    Among the biocultural innovations associated with the Neolithic, dairying and the evolution of lactose tolerance is the most studied. Expression of the enzyme lactase, which digests the milk sugar lactose, decreases after weaning in mammals, including most humans. However, some humans express lactase throughout adulthood—a trait known as lactase persistence (LP). Striking observations about LP evolution include: (i) a strong correlation between LP frequency and a history of herding and dairying; (ii) genetic patterns indicating LP-associated variants have increased in frequency through natural selection; (iii) two of these variants have been experimentally shown to affect lactase expression in adults; and (iv) archaeological and ancient DNA data indicate dairying pre-dated the rise of LP-associated variants. This chapter reviews the biology and archaeology of LP, examines some of the hypotheses formulated to explain its distribution, and outlines how simulation modelling has contributed to our understanding of its evolution."

  2. The Following User Says Thank You to paoloferrari For This Useful Post:

     FIREYWOTAN (03-09-2018)

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    REACHING A POINT OF COMPROMISE

    I appreciate the opportunity to share and thank you for a chance to add to the conversations. I've been trying to learn and qualify as many ideas and thoughts on the questions of lactose.
    Hopefully, I'm learning how to present my notions that are turning towards ideas.


    Lactase persistence
    (LP), the dominant Mendelian trait conferring the ability to digest the milk sugar lactose in adults, has risen to high frequency in central and northern Europeans in the last 20,000 years. This trait is likely
    to have conferred a selective advantage on individuals who consume appreciable amounts of unfermented milk. Some have argued for the “culture-historical hypothesis,” whereby LP alleles were rare until the advent of dairying early in the Neolithic but then rose rapidly in frequency under natural selection. Others favor the “reverse cause hypothesis,” whereby dairying was adopted in populations with proadaptive high LP allele frequencies. Analysis based on the conservation of lactase gene haplotypes indicates a recent origin and high selection coefficients for LP, although it has not been possible to say whether early Neolithic European populations were
    lactase persistent at appreciable frequencies.





    We developed a stepwise strategy for obtaining reliable nuclear ancient DNA from ancient skeletons, based on (i) the selection of
    skeletons from archaeological sites that showed excellent biomolecular preservation, (ii) obtaining highly
    reproducible human mitochondrial DNA sequences, and (iii) reliable short tandem repeat (STR) genotypes from the same specimens. By applying this experimental strategy, we have obtained
    high-confidence LP-associated genotypes from eight Neolithic and one Mesolithic human remains, using a range of strict criteria for ancient DNA work. We did not observe the allele most commonly associated with LP in Europeans, thus providing evidence for the culture-historical hypothesis, and indicating that LP was rare in early European farmers.

    Most Human Beings Are Lactose Intolerant: Here’s Why
    Arjun WaliaApril 3, 2013

    Lactose intolerance is when the body does not produce enough lactase to break down lactose, a sugar found in milk and much other milk-derived dairy products.

    The enzyme responsible for breaking down lactose is lactase, an enzyme found in the wall of the intestines. Lactase breaks down lactose (the sugar found in milk) into galactose and glucose. The activity of lactase becomes reduced after breastfeeding, at that point the body no longer needs as much lactase. Not to mention a human mothers milk is much different from the milk of a cow.

    The reduction of lactase activity after infancy is a genetically programmed event. Approximately 75 % of Earths population is lactose intolerant for a reason because it’s perfectly natural.

    The statistics vary from race to race and country to country but overall they show an abnormal amount of individuals who qualify. In some Asian countries, 90 percent of the population is lactose intolerant.

    Interestingly, we are the only species on the planet that drinks milk from another species. Since lactase’s only function is the digestion of lactose in milk, most mammal species experience a dramatic reduction in the activity of the enzyme after weaning. Lactase persistence in humans has evolved as an adaptation to the consumption of non-human milk and dairy products consumed beyond infancy. Our diet has changed a lot, and as a result, some of our genes have adapted, but it’s not an easy process. This is why most humans are lactose intolerant.

    Every other species weans and then never drinks milk again for the rest of their lives, and because of that, they don’t have an enzyme to break down the sugar in milk. But during human evolution, some humans experienced a mutation in the LTC gene, the lactase gene, these mutations allow us to process lactose as adults. With over 75 percent of humans on the planet unable to properly process it, it is evidence enough that we are not doing what is natural and in accordance with our bodies.
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    Our natural state is to be lactose intolerant. Undigested lactose in the small intestine acts like an osmotic agent, causing water and electrolytes to be pulled into the intestines, which results in diarrhea, bloating and gassiness. The body struggles and compensates, as well as protects itself by developing coping methods for our unnatural habits.

    Lactase enzyme, found in the cells lining the small intestine of mammals, cleaves lactose, a disaccharide, into the constituent monosaccharides, galactose, and glucose, which are readily absorbed by the intestine. The amount of lactase activity decreases substantially after weaning in mammals, as lactose is no more a major part of their diet. This condition in humans is referred to as lactase non-persistence (LNP) or adult-type hypolactasia or primary lactose mal-digestion (LM). In several human societies all over the world, lactose is a part of the diet of adults due to the prevalence of dairy products and fresh milk in the diet; this has been the case ever since human societies had domesticated cattle. A genetic mutation seems to have occurred in one (or more) such society (is) resulting in lactase activity persisting in the cells lining the intestine even in the adult stage. This condition is referred to as lactase persistence (LP). This mutation, due to its selective advantage, had spread extensively in such cattle rearing societies; this is the generally accepted explanation for Northern European societies having a large proportion (up to 90%) of the population being LP. Human genome sequencing studies done since 2001 have led to uncovering the molecular basis of this mutation. A single nucleotide polymorphism (SNP) at the position 13910 nucleotide upstream to the gene coding for lactase (LCT; located on chromosome 2) appears to determine the LP/LNP status of most populations studied. The nucleotide C at this position (which is the ancestral condition as determined by comparison with primate genome sequence data) corresponds to the LNP status whereas the nucleotide T at this position (which is a mutation) corresponds to the LP status. LP allele is dominant over LNP. This relationship between the SNP at -13910 upstream of LCT and LP/LNP has been verified for several populations including East Asia, East Europe etc and holds good nearly universally with the exception of some small pockets of indigenous populations in African Continent and the Arabian peninsula. Studies carried out (to be published) in the Indian population by scientists at Biotools Technologies Pvt Ltd., and a Govt. Medical Research Laboratory show that the SNP at -13910 upstream of LCT does determine LP/LNP status in Indian population as well. (1)

    A huge increase in milk alternative products like rice milk, almond milk, and coconut milk are popping up in grocery stores and convenience stores everywhere. It may be long before the truth about milk becomes more common knowledge and consumption and production wean off.

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    With all respect, Arjun Walia's article is a bit all over the place and just a little bizarre. He contends:

    ''With over 75 percent of humans on the planet unable to properly process it, it is evidence enough that we are not doing what is natural and in accordance with our bodies.''
    But then goes on to state:

    ''This mutation, due to its selective advantage, had spread extensively in such cattle rearing societies''
    I think the understanding of a selective advantage is the only thing here that is unable to be properly processed.

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    I'm indian and recently found out that i'm tolerant. Is that common among south asians?

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    There's some discussion of it in this thread: https://anthrogenica.com/showthread....se-Intolerance

    In the second post I had a few links that I think discussed frequency in South Asia. My memory is that it varies geographically within India.

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