Microbes supporting the production of more metabolic energy could be key to the evolution of large brains. This is based on a study that shows how gut microbes from different animal species shape variations in their biology.
In particular, the research offers new take on human evolution, especially in relation to the evolution of our large brains. This is based on animal studies, which showed how mice with large-brain primate microbes eat more, but grow slower and put on less body fat.
Furthermore, these mice use the excess energy to produce high levels of glucose, which is the brain’s primary fuel source.
Brain tissue is among the most energetically costly in the body, and as a result, larger-brained mammals require more energy to support brain growth and maintenance. Specifically, primates with higher encephalization quotients (EQs) (i.e. brain size relative to body size) generally have higher fasting blood glucose.
Yet determining which biological changes allowed human ancestors to meet the very high needs for energy as they evolved larger brains has remained unclear. Now a new Northwestern University study points to the role of gut microbes.
In a controlled lab experiment, researchers implanted microbes from two large-brain primate species (human and squirrel monkey), and one small-brain primate species (macaque), into mice.
The findings showed the mice with microbes from large-brain primate species produced and used more energy, while those with microbes from the small-brain species stored more energy as fat.
The research is the first to show gut microbes from different animal species shape variations in biology between animal species and supports the hypothesis that gut microbes might influence evolution by changing how an animal’s body works.
After introducing the gut microbes into microbe-free mice, the researchers measured changes in mouse physiology over time, including weight gain, fat percentage, fasting glucose, liver function and other traits. They also measured differences in the types of microbes and the compounds they were producing in each group of mice.
According to lead researcher Katherine Amato: “We know the community of microbes living in the large intestine can produce compounds that affect aspects of human biology — for example, causing changes to metabolism that can lead to insulin resistance and weight gain… Variation in the gut microbiota is an unexplored mechanism in which primate metabolism could facilitate different brain-energetic requirements.”
The strongest pattern was the difference between large-brained primates (humans and squirrel monkeys) and smaller-brained primates (macaques).
The researchers have found that the mice given microbes from the humans and squirrel monkeys had similar biology, even though these two larger-brained primate species are not close evolutionary relatives of one another. This suggests something other than shared ancestry — likely their shared trait of large brains is driving the biological similarities seen in the mice inoculated with their microbes.
Specifically, the findings suggest that when humans and squirrel monkeys both separately evolved larger brains, their microbial communities changed in similar ways to help provide the necessary energy.
The findings have been published in the journal Microbial Genomics. The study is titled “The primate gut microbiota contributes to interspecific differences in host metabolism.”
