How Human Are We?

by Samantha Grimes

People have a voracious appetite when it comes to understanding themselves as humans. When the Human Genome Project began in 1990, many people were convinced that the study would initiate an era free of disease. Once human genetic material was mapped out in its entirety, the public reasoned that researchers could then utilize this knowledge to personalize medicine and treat diseases at a genetic level.  

Nevertheless, the human genome project finished 12 years ago and maladies such as cancer, sickle-cell anemia and even Huntington disease (the first human disease gene mapped by scientists) still haunt the human system. Even though the Human Genome Project enhanced the study of human health and genetics as a whole, it offers far from a complete picture of what makes us human. In fact, while an estimated 20,000-25,000 human genes code for the proteins needed to build the human body, these genes are outnumbered in the human system by a factor of 100 to one by another set of genetic information: the microbiome. 

Including all the bacteria, archaea, fungi, protists, viruses and microscopic animals that live in and on the human body, the human microbiome is a vast and diverse community of microflora as unique as a traditional genome. The presence of microorganisms is so immense that by cell count, each person is only 10 percent “human. The potential implications of this huge store of genetic material prompted the National Institutes of Health to launch the Human Microbiome Project (HMP) in 2007 in order to study the features of humans’ microbial tenants.  

This study illuminates our relationship with microbes, one previously regarded as almost exclusively negative, suggesting that not only are most microbes benign, but many are also quite helpful in processes such as vitamin synthesis, immune response and detoxifying carcinogens 

While the research of the microbiome is still relatively new, cohort studies across the globe are beginning to highlight the extraordinary diversity of the microbiome. Microbes colonize the human body from the time of birth, but as people age, lifestyle factors such as diet, exercise, hormonal shifts, injury and even stress can influence the makeup of individual microflora. For example, diet can introduce a variety of microbial species to the microbiome, as people consume the bacteria, fungi and viruses found on foods they eat. Thus, foods rich in bacteria, such as yogurt products, introduce species like lactobacillus, which help aid digestion in the gut. This variety also helps establish a greater stability in the microbiome, maintaining health and preventing disease. Consequentially, when people eat, they eat not just for their own sustenance, but also for that of the 100 trillion cells that help to make us human.  

However, diet is not the only way in which humans shape their microbiomes to become unique. Hormonal changes, such as those controlling the production of oils on the skin, cause major adjustments in the skin’s microbial diversity especially during pubertyMeanwhile major stress responses can increase the permeability of the gut, allowing bacterial species to move and interact in novel ways. Since stabilized microbiomes help protect the body from pathogens and other bacteria that might disrupt normal levels of hormones, chemicals and neurotransmitters, these changes have led scientists to investigate how changes in diet, hormone levels and stress impact conditions like irritable bowel syndrome and depression. These studies have illuminated the importance of a healthy lifestyle, illustrating that lifestyle factors have a direct impact on the health and diversity of the microbiome.  

On another scale, while people play an active role in shaping their microbiome, many researchers are interested in determining exactly how differences in microflora can impact an individual’s risk for certain conditions and diseases. Dr. Leo Galland, Director of the Foundation for Integrated Medicine in New York, found in a 2014 study that the human gut microbiome plays a role in memory, mood, cognition and the production of hormones and neurotransmitters. Not only can bacterial species such as Escherichia coli respond to human neurotransmitters like dopamine and serotonin to regulate their gene expression, they can further produce these compounds on their own 

Dopamine is associated with focus, depression and motivation, whereas serotonin correlates with human immune response, sleep cycle and stable mood. The implication that bacterial genetics play a role in regulating these aspects of human life means that microbes might contribute significantly to how humans think and act on a regular basis. With such an intricate relationship in the human digestive system, it seems the phrase “a gut feeling,” may be an appropriate saying after all. As the link between commensal colonies and neural pathways becomes clearer, researchers may soon be able to regulate mood and immune disorders by monitoring and managing species in the gut microbiome.  

While human microflora is rich in diversity, studies suggest the most influential microbes reside in the gut, potentially impacting an even wider range of conditions. An ongoing cohort study conducted by Dr. Johanna Lampe, research professor at the University of Washington’s Department of Epidemiology, is examining the relationship between the gut microbial community and the risk of breast cancerAfter realizing the tendency for unbalanced colonies of gut bacteria to cause inflammation that increases the risk of gastric and colon cancers, Lampe launched a study that is investigating the potential for these bacteria to cause inflammation in other tissues 

Furthermore, a 2009 study on twin sets of mice at the Center for Genome Sciences found that decreased diversity in gut microbiota deceases metabolic rates and increases the resultant likelihood of obesity. Similarly, human fecal transplants, in which the bacteria from a healthy person’s stool is purified and inserted into the gut of a person with a dangerous bacterial infection, have demonstrated a 90 percent success rate in curing bacterial infections without surgery. Examining the potential consequences of unbalanced communities of microflora, these studies seek to discover the correlation between microbial variety and human health in order to establish new methods for treating conditions that are influenced by the microbiome. 

These effects, while enormous in scope and significance, are only the beginnings of researchers’ understanding of how important microflora are to human health. Eventually, microbial analysis might play a more active role in disease prevention and treatment in order to successfully combat bad bacteria while maintaining a healthy diversity in our microbiome.  

So, at the end of the day, what do all these things mean for humans, who serve as hosts to a vastly diverse community of microflora? These new studies promote the importance of traditional facets of good health, such as an adequate amount of sleep, a diet full of fruits and vegetables, regular exercise and managing stress, which directly impact the health and diversity of the microbiome. Furthermore, people can feed their microbiome by incorporating yogurt, garlic, fibrous vegetables and fermented foods like sauerkraut and kimchi into their diets. These foods add diversity to the gut microflora and help nourish the preexisting microbes living there. When people cultivate a healthy environment for their microflora, it becomes easier for these commensal species to combat pathogens, metabolize food and synthesize vitamins necessary for human survival. 

Though the scientific community and the general public are still learning about the ecosystem contained within their bodies, it remains clear that people are not as wholly human as they might have initially seemed. The trillions of microbial cells that live in and on human skin, mouths, intestines and urogenital tracts suggest that an alien world exists within the bounds of our bodies, and that we are truly just the beginning to discover what it means to be “human.”