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The fact that we are not entirely human is not exactly breaking news. A 1972 journal article by Thomas D. Luckey argues that a large percentage of the body’s cell count includes nonhuman microbes. In the article, Luckey estimates that bacterial cells outnumber human ones by around 10:1, a figure that has loomed large over microbiome research for decades.

Yet more recent research suggests we might be a little more human than we thought.

In a paper published in 2016, a team of Israeli and Canadian researchers found that 10:1 was a “back-of-the-envelope calculation” that inaccurately assumed too much bacterial density throughout the digestive tract. They revised the estimate to be around 1:1 — making us half human, half microbe. It’s still a substantial percentage, if slightly less dramatic.

The scientists also noted that this ratio is constantly in flux and that something as minor as a “defecation event” can shift the ratio in favor of the human by excreting about a third of the colonic bacterial content, if only temporarily.

They emphasized that their findings in no way diminish the biological importance of the microbiome. This collection of microbial organisms continues to play a vital role in maintaining or disrupting our health.

In that sense, we may be wise to treat it as our better half.

This article originally appeared as “Miscounting Millions of Microbes” in the June 2022 issue of Experience Life.

Courtney Helgoe

Courtney Helgoe is the Experience Life features editor.

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