Gene Sleuths Find How Some Naturally Resist Cholera

Nicholas Wade, New York Times, July 4, 2013

People living in the Ganges Delta, where cholera is an ancient, endemic and often lethal disease, have adapted genetically to the scourge through variations in about 300 genes, say researchers who have scanned their genomes for the fingerprints of evolution.

The researchers also found unexpected changes in genes that protect against arsenic, suggesting that arsenic exposure in Bangladesh is not just a modern problem associated with deep tube wells but may have ancient roots.

These instances of natural selection probably took place within the last 5,000 to 30,000 years, the researchers say, and show how evolution has continued to mold human populations through the relatively recent past.

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The genes that showed fingerprints of natural selection were identified by two other authors of the study, Elinor K. Karlsson and Dr. Pardis C. Sabeti, computational biologists at Harvard, in the genomes of Bengalis, the majority population in Bangladesh.

The selected genes offer a road map to how the body defends itself against cholera. Toxin from the bacterium binds to cells in the victim’s intestine, prizing open the channels through which chloride ions leave the cell and forcing the cells to excrete volumes of water and electrolytes—up to two liters an hour. The diarrhea benefits the organism, which can reach drinking water and spread further, but can be lethal for the host if unchecked.

One set of selected genes in the Bengalis affects control of the innate immune system, the body’s first line of defense against microbes. Another set of genes affects the channels that control the flow of potassium ions in and out of cells. It is not yet known exactly how the variations in any of the selected genes affect the biology of resisting cholera. But variations in the potassium channel genes, for instance, could help reverse the outward flow of water caused by the cholera toxin’s attack on the chloride channels.

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People with blood group O are particularly susceptible to cholera, and indeed few Bengalis have blood group O. In scanning blood group genes, the researchers were not able to pick up any negative selection against the O group genes. But they unexpectedly found evidence of natural selection having favored a minor blood type known as the Kell blood group. The genes of this group have no known connection with cholera but seem to offer a defense against arsenic. The poison contaminates the groundwater of Bangladesh, having been released by the tube wells dug to secure clean water to protect against cholera. The presence of protective genes in the Bengali population, if verified, would suggest arsenic is not just a modern problem but has been unleashed by monsoons or other natural phenomena for thousands of years.

As a necessary preliminary to testing for natural selection, the researchers looked at the racial composition of the Bengali population and found that they are an Indian population with a 9 percent admixture of East Asian genes, probably Chinese. The admixture occurred almost exactly 52 generations ago, according to statistical calculation, or around A.D. 500, assuming 29 years per generation. The Gupta empire in India was in decline at this time, but it is unclear whether the intermarriage with East Asians took place through trade or conquest. {snip}

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  • MawellAxel

    This is NOT evolution. This is ADAPTATION!!!! It is NOT the same thing!

    • Enough of those over a long enough time and you’ve eventually got different species, especially when a catastrophe produces a population bottleneck in an isolated area (genetic drift works the fastest in small, isolated populations).

    • So CAL Snowman

      Natural selection by adaptation is one of the underlying principles of evolution. We have an isolated population with genetic variation not seen in any other population on Earth. This is most definitely a prime example of evolution.

      • MadMike

        Evolution: The change of allele frequencies over time.
        Allele: Pairs of Genes one allele from each parent which determines Phenotype (characteristics).

  • JohnEngelman

    Recent evolution can also explain racial differences in average intelligence and crime rates.

  • IstvanIN

    Good golly it means these people will continue to breed and breed nonstop forever.

  • David Ashton

    “The various races, when carefully compared and measured, differ much from each other, – as in the texture of the hair, the relative proportions of all parts of the body…the form and and capacity of the skull, and even in the convolutions of the brain…also in constitution, in acclimatisation and in LIABILITY TO CERTAIN DISEASES.” – Charles Darwin, “The Descent of Man” (rev. ed. 1889), p.167.

  • APaige

    The ‘adaptation’ must have been passed on as a social construct.

    • Rhialto

      No, it means that the cholera bacteria living in the Ganges Delta are racist.

  • KenelmDigby

    As the article says, cholera is endemic in India, Indians have lived with the disease for hundreds of years – and their very genomes are shaped by the massive toll it extracted.
    As we all know the cause of cholera is human ‘faecal material’ contaminating drinking water.
    As an aside, recently a cholera epidemic ran through Haiti like wildfire killing hundreds and leaving thousands more in a state of terrible discomfort. The cause? – after the recent earthquake there, the UN sent Indian troops to Haiti for ‘peace-keeping’ roles. Apparently, ‘faecal material’ – from Indian army camps entered streams used for drinking water, and the rest is history. The Haitians now plan to sue the UN for huge damages.
    Back in the ’70s, ‘mini’ cholera outbreaks affected the environs of Paris, France. Initially the authorities were baffled. But the dilligent work of scientists soon found the cause. The outbreaks occurrred under the fligh-paths of planes operating from Paris airport. It was found that leaking waste-pipes from the toilets of Indian airplanes was the cause.

    • As an update, the UN has some sort of immunity from lawsuits like that one, and told Haiti to go get stuffed.

      An unknown early – probably hemorrhagic fever – virus exposure among whites has left us very resistant to HIV; some 10% of the global white population is immune to HIV. IMHO, 90% is still bad odds. Whites are the most resistant to tuberculosis, and European whites were the most resistant to smallpox (recurrent smallpox outbreaks in Europe killing off students from North America spurred the founding of universities here.)

      I don’t know about plague; due to its origin there, Mongolia’s natives are probably the most resistant.

      A very good read on the subject of epidemiology is “Man and Microbes”, by Arno Karlen, ISBN 0-684-82270-9

      • Spartacus

        The plague originated in India, not Mongolia, so I don’t see why Mongolians would be more resistant to it.

      • MadMike

        Bubonic Plague aka The Black Death is one theory which explains why Whites are more resistant to AIDS then other races. I also read that 10% of European Whites are immune but another 20% are resistant HIV.

  • gemjunior

    I saw that exact video and then couldn’t remember what site it was on so thanks a lot for the name of it. I wanted to show it to everyone I know because it was the most extreme example of ignorant savagery I have seen in a long time. They were drinking directly out of the river as corpses floated by, heads, limbs, etc. Crowds of people swimming and coming up out of the water between heads and legs, with a dead cow floating past once in a while. It was so disgusting it was hard to believe that any human could have the immunity to withstand this sort of thing. Drinking it one foot from cadavers in different stages of decomposition. If this is acceptable, does anyone think handwashing is important to the same people? I wouldn’t go near their food (I never did anyway because it’s gross). Can’t eat Mexican, Indian, or spicy stuff. My bland whiteness, you must understand, is so boring and unvibrant and unenriched that toast and tea , meat and potatoes is acceptable…

  • Spartacus

    Here they are, drinking and bathing in the Ganges, while a corpse floats nearby :

  • David Ashton

    Human beings could direct their own evolution (Galton, Huxley, Cattell, Glad).

    • Urban Teacher

      It is being directed, but not in the direction we would wish.

  • Watched that, and it was somewhere between really sickening and “Oh My God”; probably closer to the latter.