NIH Image Gallery
Beneficial Gut Bacteria
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 specie at about the same time. A mutually beneficial relationship between gut bacteria and animal hosts may contribute to the formation of a new species.

Credit: Darryl Leja, National Human Genome Research Institute, National Institutes of Health