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As the world grapples with a global pandemic, a study of tens of thousands of ancient skeletons has revealed how the human body evolves to fight disease, and how diseases also evolve to become less fatal over time. Its findings could teach experts more about how we will adapt to deal with diseases in the future.
The researchers behind the new study say it shows how germs mutate to replicate and ensure the survival of as many human hosts as possible – but that this behavior also reduces the severity of the disease over time. time. In the end, harmful or pathogenic microorganisms lead to a kind of truce with the human body.
Leprosy, tuberculosis and treponematoses (a group of diseases including syphilis) were the diseases analyzed in the research. They can all leave marks on bones and teeth that indicate infection, and with available human remains and medical records, they can be traced up to 200 generations.
“Each of these three diseases shows a decline in prevalence resulting from a co-adaptation that is mutually beneficial for the disease and the human host,” says anthropologist Maciej Henneberg, of Flinders University in Australia.
“In the last 5,000 years, before the advent of modern medicine, the skeletal signs of tuberculosis became less common, the skeletal manifestations of leprosy in Europe decreased after the end of the Middle Ages, while the signs Skeletal treponematoses in North America have declined, particularly in the last years before contact with European invaders.
The researchers looked at three previous studies on the three diseases, covering 69,379 skeletons in total. In all of the studies reviewed, the age of these skeletons ranged from as far back as 7250 BCE to the present day.
Not all of these skeletons were from people with tuberculosis, treponematoses or leprosy, and not all of the skeletons of people with these diseases would have shown physical signs on the bones. While that does mean the new study is not a strict epidemiological meta-analysis, it does mean the sample size was large enough that the team could make some useful speculation.
None of the three diseases immediately kill their human hosts, which helps pathogens to live and spread. But the statistically significant decline in the prevalence of tuberculosis, treponematoses or leprosy over time suggests that humans have become more immune or tolerant or that the disease has become less damaging.
“From an evolutionary standpoint, it makes sense for a pathogen to cause less damage to the host on which it depends for its survival, so high levels of transmission appear to be a temporary evolutionary trait that decreases with increasing frequency. time when we look at leprosy, tuberculosis and syphilis, ”says anthropologist Teghan Lucas of Flinders University.
While there are a few caveats to mention – such as the different ways the three studies reported on their respective results and the need to consider other factors that may affect the spread of the disease in addition to those discussed here – it’s an interesting look at the progression of diseases over time.
The COVID-19 coronavirus has only been with us for a short time, but we have already seen viruses mutate and change in order to ensure its survival and reach more human hosts. Even if vaccinations contain the spread of the virus, experts will need to closely monitor its progress in the future.
The new research is part of the growing field of paleopathology, the study of ancient human diseases through evidence such as skeletons, mummified remains, ancient documents and literature, and art.
“Paleopathology is becoming an increasingly popular discipline to study diseases that manifest on hard tissue in past populations, because the diseases preserved as long as skeletal remains exist,” says Lucas.
“Due to the preservation of pathological signs on the skeletons, it is possible to trace the co-evolution process of the three major infectious diseases as far back as specimens have been found.”
The research was published in PLOS One.
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