Microbiology

The endosymbiotic theory, confirmed by Lynn Margulis in the 1960s and now universally accepted, holds that mitochondria — the powerhouses of eukaryotic cells — were once independent alpha-proteobacteria that were engulfed by an ancestral cell roughly 1.5 billion years ago. Instead of being digested, they formed a mutually beneficial partnership. Evidence: mitochondria have their own circular DNA, divide by binary fission, and have double membranes — all hallmarks of bacterial ancestry.

For decades, scientists estimated the human body harboured 10 times more bacteria than human cells. A 2016 revision by the Weizmann Institute placed the ratio closer to 1:1 — roughly 38 trillion bacteria to 30 trillion human cells. Either way, we are as much microbial as we are human. The gut microbiome alone contains over 1,000 bacterial species and weighs about 200 grams, influencing digestion, immunity, and even mood.

Trillions of microorganisms, primarily bacteria, reside in and on your body, outnumbering human cells by a ratio closer to 1.3:1. These microbes play crucial roles in digestion, immunity, and even mood regulation.