A good part of the micro-organisms hosted by our ancestors have disappeared over the course of evolution, and this finding could lead to the emergence of very promising avenues of research in terms of public health.
The human body is a veritable biological Noah’s Ark. In addition to its own cells, our body also hosts a whole host of independent microorganisms – we talk about microbiota – and contrary to what one might think, they are not all harmful. These are often mutualistic symbiotic relationships from which both sides can benefit.
Indeed, heaps of bacteria and other small beings play a determining role in our physiology. With advances in sequencing techniques and in vivo analysis, more and more studies are beginning to document the fascinating properties of these populations.
THE ” second brain » of the human body
We can for example cite the intestinal microbiota. This one is particularly important; it is the seat of a host of processes that are essential to the proper functioning of our body. If its subtle balance is damaged, it can have very concrete physiological consequences that can be linked to diseases such as type 2 diabetes.
For these reasons, some researchers even speak of it as a full body. Some specialists even argue that the integrity of the intestinal microbiota could also affect us at the psychological and cognitive level, which sometimes leads some popularizers to speak of ” second brain “.
Many laboratories are therefore trying to develop new medical techniques centered on this microscopic fauna. These include stool transplantation, which often produces convincing results. But to master all these processes, researchers must already be able to know exactly what they are dealing with. This involves studying the nature of these microorganisms as well as their respective roles. But it is obviously very difficult given their variety.
It is on this subject that a team of biologists from Cornell University in the United States is working. In particular, they looked at the evolutionary history of the human gut microbiota by comparing it to that of bonobos and chimpanzees – the closest relatives of humans – and our closest common ancestor.
44% of our ancestor’s gut microbiota is missing
The researchers carried out metagenomic analyses. Very commonly, this consists of sequencing and studying the DNA not of a specific individual, but of an entire population of micro-organisms in the same environment – the digestive system in this case. This makes it easy to determine which species are present in the sample, and in what proportions.
After analyzing 9,640 metagenomes from humans and other primates, they pinpointed something very interesting. It turns out that 44% of the groups of microorganisms descended from the same common ancestor (or clades) that they found in the great apes were absent in humans. This figure even rises to 54% among the populations of industrialized countries. In other words, more than half of the strains of microorganisms that have evolved in contact with African great apes have abandoned the ship over the course of evolution.
A question of food?
It is important to find out why, and what it means for the future of our species. For now, researchers have not yet managed to bring a definite conclusion to this mystery. But they still make a few suggestions, including one that seems particularly promising to them: food. While our ancestor fed mainly on polysaccharides contained in the fruits and leaves of plants, the arrival of large quantities of fats and animal proteins in our diet would have considerably altered the nature of the intestinal microbiota.
“ These losses of microbiota, which affect the entire human population, regardless of lifestyle, were probably brought about by a change in diet that dates from the beginning of human evolution, shortly after we diverged from chimpanzees and bonobos. “, explains Andrew Moeller, lead author of the study.
The dynamics of the microbiota, a major issue in medicine
The implications of this finding are not yet fully clear. But they could serve as a basis for other complementary studies with much more concrete repercussions. Because beyond the differences between the great apes and our species, this study is above all a first step towards a very large-scale study of the human microbiota.
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By thus comparing the microbiota of different human populations while focusing on the strains that have disappeared from one population to another, it would be possible toidentify some of the factors that can damage these microbial populations. And knowing their importance at the physiological level, this work could lead to great progress in public health.
For example, we already know that certain antibiotics and food compounds wreak havoc on the intestinal flora. Once the dynamics of the microbiota are better understood, it will be much easier to avoid this damage upstream. Ultimately, this could also pave the way for the development of new techniques to regenerate it easily, which could make it possible to treat very disabling syndromes whose origins are still unclear today.
The text of the study is available here.