Review of Amato, "Incorporating the Gut Microbiota Into Models of Human and Non-Human Primate Ecology and Evolution"
by Jennifer Fortunato
In this paper the author, Dr. Katherine Amato, discusses the relevance of the gut microbiota to the ecology and evolution of humans and non-human primates. Amato initially discusses how the gut microbiome is an important, yet understudied, factor in biological models, including humans and non-human primates. This paper suggests that researchers should incorporate the gut microbiome into their research to expand our perspective on and test the importance of the gut microbiome in human ecology and evolution. It does so by first reviewing current knowledge about the gut microbiome and its evolutionary role, then discusses the multitude of possible impacts that the gut microbiome can have on diet, energetics, disease resistance and cognition while also suggesting areas of future research.
The initial part of this paper discusses the relevance of gut microbiome interactions in early development, the physiology of the body, and diet and nutrition. In early mammal development, the initial establishment of the gut microbiome is during and after birth, through horizontal transfer from the vaginal microbiota and social interactions with the mother and vertical transmission through breast milk, from mother to offspring. Genotype plays a role in the type of microbiota in an individual. For example, monozygotic twins have more similar gut microbiota even after living apart than couples who live together. Yet, the abundance of microbes is primarily driven by diet and physiology. Changes in nutrients can change the abundances of certain taxa of microbes. However, the microbiome can affect what the host eats based of the ability of the microbiota to digest certain compounds. For example, since vertebrates lack the enzyme to digest cellulose it is left for the microbes in your gut to be able to digest it into usable substances. The gut microbiome also interacts with physiology. It can interact with the immune system by reducing inflammation and increasing immune responses to pathogens. The gut microbiome can also interact with the endocrine and nervous system where hormones such as dopamine can affect the function and composition of the gut microbiome. Also, research has shown that administration of certain bacterial strains can positively affect stress, anxiety, and depression. Another interaction of gut microbiota and the nervous system is that the gut microbiome can impact brain development by altering gene expression which could impact cognition.
The next part of the paper discusses how the gut microbiome can be relevant to primate ecology and evolution, both in non-human primates and humans. This part specifically discusses feeding ecology and dietary niches, metabolic demands and physiology, disease resistance and health, and cognition, personality, and social behavior. For feeding ecology, in both human and non-human primates, the gut microbiome changes based on the type of food that the organism is eating and might play a role in the ability for these organisms to vary their diet in different environments for different food sources. The metabolic demands and physiology, of both human and non-human primates, interact with the gut microbiome by changing the permeability of the gut to change the nutrient absorption of the host. It is also suggested in the paper that the gut microbiome has an impact on brain size and growth rate due to this changing absorption rate of nutrients where if the microbes increase the absorption rate then that could have led to increased brain size due to the increased energy availability. Amato also discusses the importance of the gut microbiome in disease resistance and health. In both non-human primates and humans, the gut microbiome abundance and diversity can contribute to decreasing infection rates. This is brought up as corresponding to sociality, where taxa who are more social may have high microbial diversity or due to having high microbial diversity sociality is able to be maintained. Finally, Amato discusses non-human primates and human cognition, personality and social behavior in relation to the gut microbiome. Amato cites research done on how changes in the gut microbiome has been shown to affect aggression, anxiety levels, risk-taking, and social hierarchy. Amato also suggests that the human nervous system may have evolved to require microbial exposure for proper social development due to microbial ability to produce neurotransmitters, such as GABA, during early childhood development of the nervous system.
Overall, Amato urges researchers to collaborate and connect gut microbiome research with anthropological research so that we can further our understanding of primate ecology and evolution. Amato ends the paper with a multitude of questions such as: “What constitutes as beneficial or a detrimental gut microbiota?” and “Do different gut microbial stable states provide different fitness effects for the host?” that will assist in furthering the field. However, the author does caution that correlations between the gut microbiome diversity and composition does not indicate causality. She recommends that future research of the gut microbiome complements studies of human ecology and evolution through collaboration to answer questions about how the gut microbiome influences human biology.
This paper is especially relevant to neuroanthropology as it discusses how the gut microbiome could have impacts on sociality, brain size evolution and cognition. From previous readings in the class (Example: Dunbar and Shultz 2007), we have seen how important all of these factors have been in the evolution of primates. My questions for everyone are:
1. How would you design an experiment to test a gut microbiome and brain interaction using neuroanthropological methods?
2. Would you consider abundance or the type of microbiota more important or are both equally important and why?
3. Do you think the gut microbiome is important in primate ecology and evolution? Or do you think that there are other factors that are more relevant to primate ecology and evolution? Why?