How Human Are We biologically?

Humans have far more microbial cells than human cells in their bodies. According to one estimate, the average human body contains about 30 trillion human cells and 39 trillion microbial cells. This means that microbial cells outnumber human cells by a ratio of about 1.3 to 1.

By cell count, humans are only about 43% human, with the rest being microbial cells. As Rob Knight, a professor at UC San Diego, stated: “So to our 30 trillion human cells, we have on average about 39 trillion microbial cells. So by that measure, we’re only about 43% human.”

These microbes include bacteria, viruses, and fungi that exist in various parts of the human body, including the mouth, skin, and gut.

The collection of microbes in each person is unique and can significantly impact health, weight, mood, and susceptibility to certain diseases.

About 70% of the human body’s immune cells are thought to exist in the gut.

It’s important to note that while the number of microbial cells outnumbers human cells, this doesn’t mean microbes make up most of our body mass. Human cells are much larger than bacterial cells, so by mass, humans are still predominantly human. The exact numbers and ratios can also vary between individuals and may change over time based on factors like diet, environment, and health status.