The Aliens We’ve Already Discovered

One of the fascinating ideas in our new travelling exhibit Alien Worlds & Androids is that some of the strangest aliens are inside our own bodies, a home to trillions of weird, intricate life forms that we call the human microbiota.

The individual life forms are called microbes, which are organisms distinct from our own cells, including bacteria, archaea, fungi, protists, viruses or other microscopic animals. They live in our skin, glands, fluids, organs, saliva, and gastrointestinal tracts. And there are trillions of them. It’s technically accurate to say that human beings have been “colonized.”


The typical estimate states that we live with 10 times more alien cells than cells of our own. Though precisely counting cells is very difficult, we know our bodies also contain trillions of our “own” human cells. More recent studies have suggested that the figure is closer to 3 alien cells for every one human cell. Regardless, it does make you wonder what these aliens are up to.


Some microbes cause disease, but most are either harmless or helpful. Our skin is covered by hundreds of species of bacteria that keep our skin healthy. Beneficial bacteria in our mouth prevent yeast and fungal infections. We have pounds — yes, pounds — of bacteria in our guts that help us digest food. Though we don’t know what most of our microbiota are doing, what we have learned has been extremely useful to different fields of medicine — like treating cancer and gastrointestinal disease. This is one reason why research about these tiny residents is so popular, and important.

As an example, the NIH’s Human Microbiome Project took five years to analyze the genetics of our microscopic ecosystem, with particular focus on the organisms that live in our skin, mouth, nose and gut. It published its milestone results in 2012!

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