Gut Microbiome

Certainty Style Key
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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Relative Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
MOCA Domain: 
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In a recent comparison of gut microbial diversity from 160 wild chimpanzees, 70 wild bonobos, 186 wild gorillas, and >500 humans, across five different populations ranging from urban to hunter-gatherer lifestyles, it was found that humans have lost microbial diversity compared to the wild great apes. This change is hypothesized to be the result of increased consumption of meat.

Background Information: 

The gut bacteria of mammals are highly diverse and generally the composition of a mammal's gut microbes reflects their diet.  For instance, herbivores harbor more similar suites of bacteria compared to carnivores. The richness of the gut microbiota is also related to diet, with herbivores generally harboring the most complex microbial assemblages (highest number of "species" of microbes), and carnivores the least.  This presumably reflects the need for microbial assemblages to work together to break down complex polysaccharides from plants, whereas richer, simpler diets comprised of meats are more easily broken down and do not require specialized enzymes or thermodynamically-based microbial symbioses. There is an additional force shaping the gut microbial communities of mammals: animals with similar gut physiologies tend to have similar microbial communities (eg, foregut fermenters vs hindgut fermenters).  In this context, chimpanzees and humans have similar diet, gut structures and thus both species have grossly similar gut microbial assemblages typical of omnivorous primates.

The Human Difference: 

Humans and the Great apes share a core set of bacterial genera and co-occurance patterns across those taxa were highly consistent. However, the relative abundance of Bacteroides, which are associated with diets rich in animal meat, are increased five fold in humans. Conversely, Methanobrevibacter and Fibrobacter, both involved in the degradation of plant matter, are greatly reduced in humans.

Universality in Human Populations: 

Humans are by far the most studied animal, and this is true for the characterization of the microbial assemblages in the gut as well. Comparison of >500 humans from lifestyles that include urban US and Europe, rural Malawi, preindustrial southern Amazon rainforest, and hunter-gatherer in Tanzania found that all groups showed lower levels of microbial diversity than that of wild apes.

Mechanisms Responsible for the Difference: 

As carnivores show the least microbial diversity, increased meat consumption could explain the loss of microbial complexity.

Implications for Understanding Modern Humans: 

Since the gut microbes are implicated in energy balance, and in contributing to the body weight of the host, a greater understanding of the differences between humans and their close relatives may shed light on whether gut microbes helped shape the evolution of humans and in particular if they played a role in the proposed trade-off bewteen large gut and large brain.

Related MOCA Topics
Referenced By:
Title Certainty
Cuisine Speculative
Detoxifying/Removing Antinutrients Likely
Milk Composition True


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