To the general surprise, evidence of malaria has been detected in hunter-gatherers living in Vietnam 7,000 years and more ago. The discovery changes our understanding of the evolution of human beings’ relationship with the malaria parasite.
The thinking had been that the relationship between parasite and human was associated with the advent of agriculture. But farming didn’t begin in that area of southeast Asia until thousands of years later, after malaria was already plaguing local hunters and gatherers, says a new paper in Scientific Reports.
Rice cultivation began in China perhaps around 11,000 years ago, but only seems to have spread from there to northern Vietnam about 4,500 years ago at the earliest, but more generally, 4,000 years ago.
Before the local development of grain cultivation, the people in this region were pre-Neolithic foragers descended from the first humans to exit Africa and survive. But by 7,000 years ago these people were creating settlements in northern Vietnam, even without farming – and it seems they suffered from malaria.
Malaria does not leave morphological traces on bones that we know of, but a genetic disease called thalassemia can do that. What the archaeologists actually found was hallmarks of thalassemia damage among prehistoric hunter-gatherers in southeast Asia.
The survival of the thalassemia genes (it’s a whole group) in turn indicates that these hunter-gatherers suffered from malaria.
Thalassemia is a sometimes mild, sometimes deadly inherited disorder in the manufacture of hemoglobin. But it has an upside: It confers some resistance to malaria by disrupting the mechanism by which the malaria parasite binds to red blood cells. That is why the gene survives in human populations. Survives? It thrives: Significant proportions of the population in Southeast Asia, up to over 70% in some, bear thalassemia-related genes. The rates are extremely high in today’s Vietnam.
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It bears adding that a much smaller percentage, in the low single digits, actually develop symptoms of the condition, which may in bad cases include skeletal distortions, including of the face, creating what doctors call “rodent facies” or “chipmunk facies”. Such were found now by the archaeologists.
Where the mosquito flies
In the Levant, farming began over 10,000 years ago. As we cleared land and watered crops, we increased our exposure to the Anopheles and some other variants of mosquito that carry the malaria parasite. (Mosquitoes breed in stagnant water.)
It is still the prevailing opinion that selection for thalassemia in the Mediterranean region was indeed driven by our enhanced exposure to Anopheles, explain the authors of the new paper. But the notion that malaria only became a global threat to humans after farming began is evidently a fallacy. “In Southeast Asia this disease was a threat to human groups well before that,” said lead author Dr. Melandri Vlok, from the University of Otago, New Zealand.
Thalassamia is actually an inherited group of disorders. All its forms result in inferior hemoglobin in the blood. Being genetic, it’s non-transferrable. When mild, the condition may cause anemia and fatigue and may not require treatment. Severe forms are treated with blood infusions. At present thalassemia is common where Anopheles flies: Africa and Asia, and around the Mediterranean basin, including in the Middle East, Turkey and Greece.
Crucially to this paper, thalassemia leaves telltale signals in human bones, which the authors detected by both macroscopic and microscopic means in populations of both prehistoric hunter-gatherers of Vietnam, known as the Con Co Ngua, and in the later early farmers, the Man Bac.
The Con Co Ngua hunter-gatherers are the older culture, existing there from about 8,000 to 7,000 years ago; the Man Bac were early farmers lived who from about 4,000 to 3,500 years ago.
In 2018 a separate paper on the Con Co Ngua debunked another myth: that the transition from a lifestyle of hunting and gathering to sedentarism and farming made us sicker. Not exactly: Both societies seemed to be in lousy health, they just suffered from different conditions, the archaeologists concluded. One they shared, probably, was malaria.
“Firstly, our findings demonstrate that thalassemia emerged prior to the transition to agriculture in Mainland Southeast Asia, from at least the early seventh millennium before the present, contradicting a long-held assumption that agriculture was the main driver for an increase in malaria in Southeast Asia,” the team writes.
In addition, the researchers detected a significant malarial burden among the early farmers in the region, again based on signals of thalassemia. Ergo it wasn’t the introduction of farming and irrigation creating stagnant water the insect needs to breed, that exposed the peoples of southeast Asia to the dread Anopheles, which in turn drove for the selection of thalassemia genes. The mosquito liked it there all along.
All this remains hypothetical but it makes sense, really, given the climate. The team also notes the separate report on archaeological evidence for hereditary anemia in Khok Phanom Di, a Neolithic site in central Thailand, dating to about 4,000 to 3,500 years ago.
The severity of thalassemia symptoms, when the disease kicks in, is indicative of just how serious the problem of malaria is, and remains to this day. There are several variants of the disease, which killed about 409,000 out of 229 million diagnosed cases in 2019 alone, according to the CDC. At least in stark contrast to another plague of mankind, the coronavirus, malaria isn’t infectious person-to-person. You can’t give it to anyone, except (rarely) through blood transfusions or in the process of giving birth. It takes a mosquito.
But like the coronavirus, and Ebola, it can stick around, hiding silently in the niches of your body. And then one day it can arise from dormancy.
And there’s another point: Global warming is expected to drive more extreme weather, which is expected to drive more flooding in some areas, which can also encourage mosquitoes to breed. Researchers at Yale University noted last year that climate change can be expected to expose half the world’s people to mosquitoes that spread disease, not only malaria, by the year 2050. Just to quote one statistic: They found that in the United States, the common mosquito Aedes aegypti had spread northward at a pace of about 150 miles per year. By 2050 the insect is expected to reach Chicago, a city more famous for freezing winds and storms than balmy puddles where mosquitoes like to lay eggs.
That American-centric paper didn’t dwell on malaria, but as the United Nations has pointed out, the relationship between climate change and malaria specifically is complex – and may not be possible to quantify, at least any time soon. Theoretically, rising average temperatures plus global travel (which seems likely to resume the second COVID-19 related lockdowns allow) have the potential to reintroduce or increase transmission of malaria in many countries that had eliminated the disease entirely (Israel among them) or controlled its transmission.
“Such countries would be prone to epidemics, since surveillance and preparedness for malaria control may not be as intense as when malaria was a major public health problem,” the UN adds. And, inadvertantly driving home the point about why the genes for thalassemia have persisted, “The economics of decreasing malaria transmission by mitigating climatic changes via carbon dioxide emissions, versus using other methods, have been modelled,” the UN helpfully elaborates. “It is estimated that for the cost of saving one life by cutting down on carbon, 78,000 lives may be saved annually by using mosquito nets, environmentally safe indoor DDT sprays, and subsidies for effective, new combination therapies.”