The Human Menagerie
We tend to think of ourselves as a single organism made up of human cells with specific purposes. Liver cells, brain cells, red blood cells all coming together to create....us, human beings. However, the truth is more complicated. Human beings consist of human cells, yes, but also what's known as the human microbiota, an aggregate of microorganisms such as bacteria and fungi, that live on and in the human body performing essential tasks.
It was believed that the human microbiota far outnumbered human cells with some estimates providing ratios of 10-1 or even 100-1 bacteria to human cells. However, more recently those ratios have been increasingly viewed with skepticism and now a study recently released is suggesting that ratio is probably closer to 1-1.
Here is an interesting article from ScienceNews detailing that study:
Body's bacteria don't outnumber human cells so much after all
Human bodies don't contain 10 times as many bacteria as human cells, new calculations suggest. A "standard man" weighing 70 kilograms has roughly the same number of bacteria and human cells in his body, researchers report online January 6 at bioRxiv.org. This average guy would be composed of about 40 trillion bacteria and 30 trillion human cells, calculate researchers at the Weizmann Institute of Science in Rehovot, Israel, and the Hospital for Sick Children in Toronto. That's a ratio of 1.3 bacteria to every one human cell.
That estimate could be off by as much as 25 percent, with the average number of bacteria ranging from 30 trillion to 50 trillion. Among individual people, the bacterial count could vary as much as 52 percent, say Ron Sender, Shai Fuchs and Ron Milo. With a fudge factor of 10 trillion to 20 trillion bacteria, the number of microbes may pretty well match the number of human cells in the body, which also varies somewhat. "Indeed, the numbers are similar enough that each defecation event may flip the ratio to favor human cells over bacteria," the researchers write.
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