![Bacteria in the gut The gut, a big pink sack filled with colorful pellets, strands and y-shaped branches representing the different bacteria strains](/sites/nihrecord/files/styles/thumbnail_small/public/2021/November-26/20211126-cvr%20gut%20bacteria.jpg?itok=rWRiTfML)
On the Cover
Bacterial strains in the guts of humans and chimpanzees diverged and began to evolve separately 5 million years ago, and 15 million years ago in humans and gorillas. Humans and apes evolved into a new species at about the same time. A mutually beneficial relationship between gut bacteria and animal hosts may contribute to formation of a new species.
Darryl Leja, NHGRI