It was discovered in a study, carried out by the University of Texas that microbes responsible for our intestinal microbiome have evolved alongside humans for millions of years.

Over the years, researchers have analyzed the fecal bacteria of many mammals. Besides discovering that most microbes come from heritage rather than from the environment, it was determined that intestinal bacteria were within humans at the earliest stages of evolution.

The DNA sequences of evolving genes that are common in the microbiome were compared and classified into different “family trees.” Image Credit: Science Mag
The DNA sequences of evolving genes that are common in the microbiome were compared and classified into different “family trees.” Image Credit: Science Mag

The evolution of apes and humans’ gut bacteria

Evolutionary scientist Andrew Moeller directed the study on the fecal matter of 47 Tanzanian chimpanzees, 24 Congolese bonobos, 24 Cameroonian gorillas, and 16 humans from Connecticut. The fecal samples contained positive samples of the microbes present in the host animal’s digestive tract. Each version of the same microbe was analyzed, and they managed to lay down specific parameters for at least 20 percent of the subject’s gut microbiome.

Two out of three major family trees appeared to come from a common ancestor over 15 million years ago. The gut bacteria seemed to differ as different species of apes surfaced and set themselves apart from their common ancestor. The theory is that as apes evolved towards different genera in Africa, the bacteria also evolved into different strains. It appears that gut bacteria grew at the same rate as the host species did.

The two common trees were Bacteroidaceae and Bifidobacteriaceae, whose structure had striking similarities to the evolutionary tree of apes and humans. On the other hand, the remaining tree known as Lachnospiraceae is known to form spores, thus being able to live in the environment for prolonged periods of time before being ingested by a host. This allows for bacteria belonging to the Lachnospiraceae family to be transmitted from one host o another.

Now, where did they come from?

Moeller pointed out that it is known that apes and humans shared similar bacteria on their digestive tract, but still there is no data as to where did this bacteria come from originally. It is not clear whether they were formed from within the organism or if they were acquired from the environment.

A previous study suggests that the different strains of gut microbes are due to evolutionary changes in diet and the environment. The study also proposed the idea that both gut bacteria and host ape evolved in parallel. Previous research efforts have noted that the gut microbes in humans initially come from the birth canal that joins mother and child. Interaction with other species and the environment also serve for means of germ transmission.

 Researchers theorize that both methods of transmission may be responsible for the transcendental appearance of gut microbes. Image Credit: Science Mag
Researchers theorize that both methods of transmission may be responsible for the original appearance of gut bacteria. Image Credit: Science Mag

“It’s surprising that our gut microbes, which we could get from many sources in the environment, have actually been co-evolving inside us for such a long time,” lead researcher Professor Howard Ochman stated.

Tracing evolution thanks to gut bacteria

On the last stage of the research, the same DNA samples were once more compared, but this time by analyzing people from Malawi and then people from Connecticut. The results lined up to expectations, as it appears that the bacteria of the African participants set themselves apart from the ones present in Americans around 1.7 million years ago. Coincidentally, it is estimated that the earliest exodus of humans from Africa occurred in that same period. Moeller suggested that gut microbe strains will serve to track down the migratory history of a particular species.

The results of the study are of great importance, as it has finally proven that gut microbes can evolve alongside their hosts for millions of years. Some scientists also noted that the presence of bacteria at the time of pregnancy might be of considerable significance since it may be the most critical period for a child to develop its digestive tract microbiome in a healthy manner.

With each passing day, gut microbes gain more understanding as they are vital for digestive processes and for keeping an overall integral state of health. Perhaps, the evolution of gut bacteria may provide new leads to discovering the inherent reasons why some people are sensitive to gluten, lactose, and other compounds that place restraints on what they can and cannot ingest.

An evolutionary approach to something that is alive within us, as it is the case of gut microbes, will surely be of great use for researchers trying to comprehend the origin of chronic diseases and ailments that weigh on patients for the rest of their lives. Understanding the source of a disease means that it is possible to predict its evolution, which in turn, would allow for the development of cures and treatments so that the incidence of diet-related ailments is reduced thanks to the scientific advances following this research.

Scientists recognize that the success of humans as links in the evolution of mammals lies in being able to control how much food we ingest, while also being able to select specific nutrients and their variety, all through agriculture, cooking, and shopping at our local convenience store. Although this is a vital factor as to why humans were able to overcome the evolutionary process, the possibility of choosing what we eat does not impact the major bacterial lineages that make up our intestinal microbiome.

Source: Science