United States: Scientists believe the microbes in our guts helped humans grow bigger brains. Lab experiments showed that our gut microbiomes focus on producing energy to feed our brains, unlike other animals whose guts store energy. Northwestern University scientist Katherine Amato said that what happens in the gut could be the key to how our brains developed over time.
Brain tissue is metabolically expensive, and so our bodies would have had to change in a whole host of ways to house our larger thinking organs. But the researchers were curious about just how — perhaps — our helpful microbes, living in our guts, might have been responsible for these transformations.
As reported by the Science alert, “We know the community of microbes living in the large intestine can produce compounds that affect aspects of human biology, for example, stimulating changes in metabolism that can cause insulin resistance and gain in weight,” says Amato.
“However, we have not explored how variation in the gut microbiota is an unexplored mechanism whereby primate metabolism could support different brain-energetic requirements.”
To compare the effects of the three different primate microbiomes, Amato and colleagues seeded ‘germ free’ mice with the primate microbiomes. They gave the mice gut microbes from humans (Homo sapiens), squirrel monkeys (Saimiri boliviensis) and macaques (Macaca mulatta), and then carefully monitored the mice with weight checks, liver function, fat percentage and fasting glucose.
Both humans and squirrel monkeys are classed as ‘brain-prioritizing’ and grown into relatively big brains for the size of their bodies. On the other hand, macaques’ brains are much smaller compared to the body size.’
Mice inoculated with the human gut microbiome had the highest fasting glucose, the greatest triglycerides, the lowest cholesterol, and the least weight gain. The finding hereby also suggests that the human gut microbiome prefers that host make brain feeding sugar, rather than storing energy in fats.
These differences between the mice inoculated with the human microbiome and all the other primates were anticipated, but the biggest differences were between the two big-brained species (humans and squirrel monkeys) and the one with the smallest brain (macaques).
For example, the squirrel monkeys were distantly related to us, but nonetheless had microbes that also shifted the host metabolism of the squirrel monkeys to favor energy use and production, as opposed to energy storage in the fat tissue as those of the macaques.