It takes a huge amount of energy for human brains to grow to their current large size and be maintained over time. Our early human ancestors evolved to grow bigger brains, but the biological changes they went through to do so have been difficult for scientists to pin down. Now, new research points to our guts. The secret to our big brain may lie in the microbes that help the body break down food and produce energy. The findings are detailed in a study published December 2 in the journal Microbial Genomics.
Since brain tissue is energetically costly to the body, larger-brained animals like humans, elephants, whales, and dolphins need more energy to support the brain’s growth and general upkeep. Earlier studies have explored how different genes and the environment influence primates with larger and smaller brains. However, there is less data on how different primates use energy and how metabolism develops in different primate species.
“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,” study co-author and Northwestern University biological anthropologist Katherine Amato said in a statement. “Variation in the gut microbiota is an unexplored mechanism in which primate metabolism could facilitate different brain-energetic requirements,” Amato said.
In a controlled experiment, Amato and a team of scientists implanted the microbes from two large-brain primate species (human and squirrel monkey), and one small-brain primate species (macaque), into laboratory mice.
After introducing the gut microbes into microbe-free mice, they measured the changes in mouse physiology over time. These changes include
