Posted by Carlota Dopico – Business Development & Innovation Manager – 12/07/2025
Just as it sounds — this is neither a metaphor nor an exaggeration. It’s a fact: more than half of the cells living in your body are not human. They’re bacteria, fungi, viruses, archaea
And if you look at the genetic information, the proportion is even more striking: around 99% of the genes present in our bodies come from these microorganisms — not from our nuclear DNA. In other words, most of the genetic material we carry belongs to other living beings.
We are holobionts: living communities made up of thousands of species that coexist, evolve and depend on each other to survive.
How we came to understand it: a brief true story
The first person to glimpse this invisible world was Antonie van Leeuwenhoek, back in the 17th century, with a microscope that was as simple as it was powerful. When he focused on a drop of water, he saw what he described as “animalcules” — tiny creatures unseen to the naked eye. And when he looked inside his own mouth, he discovered a microscopic zoo.
That vision forever changed our understanding of who we are: the body was not alone. But for centuries, medicine went down another path.
In the late 19th century, Robert Koch and his postulates cemented the idea that every microbe was a potential enemy: if it caused disease, it had to be isolated, killed, eradicated. With Pasteur’s discoveries and the era of antibiotics, the war against microbes became the dominant paradigm. It saved us from deadly epidemics
By the 20th century, the idea that all microbes were enemies began to shift: many turned out to be silent allies, fundamental to our survival. One pioneer was the scientist Élie Metchnikoff, who suggested that certain microbes could actually be beneficial. He discovered that the gut “flora” helped protect us and proposed that fermented foods could prolong life. Today, we know that the term “flora” is inaccurate — bacteria are not plants — so we speak of the microbiota or microbiome instead.
These were ideas ahead of their time, but they were overshadowed by the antibiotic era.
The turning point: decoding the microbiome
It wasn’t until the early 21st century that everything changed. In 2001, Nobel Prize winner Joshua Lederberg coined the term microbiome to describe not only the microorganisms that inhabit us, but also their genome and their impact on our biology.
With the launch of the Human Microbiome Project (2007), a new map began to emerge: for the first time, we sequenced the DNA of our billions of invisible companions. The results shattered old myths: without microbes, we are not viable. They digest what we cannot do alone, shape our immune system, regulate vital processes, and protect us from invaders.
Being a holobiont: an interdependent ecosystem
Each person is a shared microcosm. Your gut microbiota alone can host up to 1.000 different species; just on your skin, billions of microorganisms live to protect you. Every kiss, every journey, every touch leaves a biological trace.
Today, we know that the loss of microbial diversity — dysbiosis — is linked to allergies, inflammatory diseases, metabolic disorders and neurological conditions. The paradox: the same civilization that eradicated infectious epidemics has impoverished the ecosystem that keeps us healthy.
Recognizing ourselves as holobionts redefines how we understand health, disease, and life itself.
We are not closed units: we are open systems, shaped and protected by thousands of invisible species. Taking care of them means taking care of our most essential part.
