Ancient Human Microbes: Are They Filled With Clues of The Past?
Humans have always had an interesting relationship with the small things of the world. We have been plagued by pathogenic bacteria, viruses and parasites for our entire history. There are more bacteria in us than there is humans, with the number of bacteria being much larger than the number of human cells in our bodies, outnumbering them by at least ten times (Warinner et al. 2014). But humans have also been helped by these microbes which include fungi, bacteria, archaea, viruses, algae and protozoa. Micro bacteria has been linked to learning and memory in humans and animals as well, which may have been a major stepping stone to the evolved man that we have today (Parashar 2016). With new technology scientists are finding that the microbes in the human body, from the distant past to the present, have evolved at the same rate if not faster than we as species have, which can lead to clues of our distant past that may help us better understand ourselves now.
Microbes have shaped humans as they are today through affecting the development and immunization of certain viruses and diseases, as well as impacting human behaviours and brain development. A lack of microbes can even cause detrimental effects. In a study using sterile mice without any microbe growth, the lack of microbes had led to autistic-like behaviour which lead to the hypothesis that microbes affect behaviour and mental cognition in other animals as well (Dinan 2015).These findings suggest that without our microbes, the human race could experience higher rates of cognitive impairment, or possibly even higher fatality rates. The human race’s relationship with the small things of the world is an intricate and extremely important one. Additionally, microbes are specific to each host.
Microbes can also be used to track the history of human evolution. One good example of this is Mycobacterium leprae, the bacterium that causes the disease leprosy. By connecting historic genetics with the strains of M. leprae that affect certain populations of people, we can track the heritage of those people through the spread of the disease strains. In addition, we can compare strains from today with strains from long ago due to the fact that M. leprae’s genome has been well preserved in the last millennium (Cardona-Castro et al. 2015). This can allow us a look into the evolution of human immunity, as well as the genetic differences between different populations of humans in the past. This can be incredibly useful, not only from a historical standpoint but also from a biological and medical standpoint. If we know where we came from, it can give us better insight on our genetics and immunity now.
Another use of microbes is gaining valuable insight on the genetics of modern pathogens so as to better combat them. For example, Mycobacterium tuberculosis was thought to have originated in humans 4,000 years ago from a mutation in Mycobacterium bovis, which was a relatively harmless bacteria found in wild cattle (Karlen 1995). Utilizing the tools made available by advancements in the field of ancient DNA analysis, researchers can take the fossil of a human they know to have lived in a certain geographic area and epoch and, upon finding the presence of M. tuberculosis, form hypotheses about the conditions under which M. tuberculosis can thrive (Spigelman 1993, Donoghue et al. 2004). Medical researchers could hypothetically use this knowledge to develop more efficient methods of fighting modern strains of tuberculosis. This is just one case of the way ancient microbes can help us fight modern ones.
The effect of a given microbe on a given host varies widely. In a review article by Jun Sun conducted in 2014 on gut stomach microbes in human health and disease, Sun states “microbes do not occur randomly and are highly dependent on host factors and environmental cues and once they are fully developed the gut microbes become ‘essential’ and provide many vital functions for the host” (Sun 2014). This quote states that microbes do not just evolve, but are all specific to each host and will evolve according to the area in which the individual lives. They will also either evolve positively or negatively, depending on where migrations or individuals reside. Thus, each host will respond differently to microbes.
Microbes are exponentially numerous, powerful and essential to the human race’s well-being. Without microbes, all life on Earth would most likely die out very quickly. It has been hypothesized that without bacteria, humans would not have developed to the present level of cognitive performance that characterize us as the social and dynamic animals that we are today (Dinan 2015). Microbes are crucial to the survival of not only humans, but the planet itself. With continuing rapid advancements in the field of DNA analysis, the scientific community is realizing we have only scraped the surface of the wealth of knowledge to be gained from understanding these fascinating microorganisms.
Cardona-Castro N, Cortés E, Beltrán C, Romero M, Badel-Mogollón JE, Bedoya G. 2015. Human Genetic Ancestral Composition Correlates with the Origin of Mycobacterium leprae Strains in a Leprosy Endemic Population. PLoS Neglected Tropical Diseases. 9:1–16.
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