Meme #10 - Holobiont

In Entangled Life, Merlin Sheldrake deepens the concept of symbiosis to include all the microscopic life forms that share bodies with humans and other organisms. His brief history states: 

[In the 1950s, biologist Joshua Lederberg] found that bacteria could trade genes with each other. One bacterium could acquire a trait from another bacterium “horizontally.” Characteristics acquired horizontally are those that aren’t inherited “vertically” from one’s parents. One picks them up along the way. (p.77) 

In this way, a bacterium can acquire characteristics “ready-made,” speeding up evolution many times over. (p.78) 

In 1967, the visionary American biologist Lynn Margulis became a vocal proponent of a controversial theory that gave symbiosis a central role in the evolution of early life. Margulis argued that some of the most significant moments in evolution had resulted from the coming together - and staying together - of different organisms. Eukaryotes [cells or organisms that possess clearly defined nucleuses] arose when a single-celled organism engulfed a bacterium, which continued to live symbiotically inside it. Mitochondria [that generate energy from oxygen] were the descendants of these bacteria. Chloroplasts [that generate sugars and lipids from sunlight] were the descendants of photosynthetic bacteria that had been engulfed by an early eukaryotic cell. All complex life that followed, human life included, was a story of the long-lasting “intimacy of strangers.” (pp.80-81) 

The endosymbiotic theory, as it came to be known, rewrote the history of life. It was one of the twentieth century’s most dramatic shifts in biological consensus. (p.81) 

It is no longer possible to conceive of any organism - humans included - as distinct from microbial communities they share a body with. The biological identity of most organisms can’t be pried apart from the life of their microbial symbionts. The word ecology has its roots in the Greek word oikos, meaning “house,” “household,” or “dwelling place.” Our bodies, like those of all other organisms, are dwelling places. Life is nested biomes all the way down. (p.91) 

We can’t be defined on anatomical grounds because our bodies are shared with microbes and consist of more microbial cells than our “own” – cows can’t eat grass, for example, but their microbial populations can, and cows’ bodies have evolved to house the microbes that sustain them. (p.91) 

Some researchers use the term “holobiont” to refer to an assemblage of different organisms that behave as a unit. (p.92) 

The concept of holobiont takes our view of symbiosis beyond “organisms interacting along a spectrum between parasitism and mutually beneficial partnerships” and into a way of thinking that sees all organisms as a “single unit.” Are the fungi and other microbes found in our guts creatures distinct and separate from ourselves or are we all one? If we take the holobiont perspective the answer is simple: we are all one organism, and the implications are mind-bending. It means that the microbiomes in our guts are not just internal ecologies that must be studied and managed. Instead, they are “us” in the same way that our hands, feet, hearts, and spleens are “us.” Appendages like hands and feet must sometimes be sacrificed for the survival of the individual but never without a great deal of consideration and somber reflection about the loss to the person - the same should hold true for our microscopic parts too. Also, taking the idea of holobiont to its logical conclusion means we must now recognize that external ecologies are not separate from us either – that we are like microbes living on the body of the Earth. From this point of view, polluting a river would be exactly like swallowing poison that makes us sick or kills us. Obviously, this type of calculation would greatly affect behavior.

Viewing all life as a single, giant holobiont would not only promote more responsible behavior, but it might also provide new solutions to big problems. Horizontal gene transfer showed that biology is much more fluid than we once imagined and that things can advance more speedily than we once believed. Hundreds of millions of years of evolution were bypassed through the introduction of bacteria that could 1) generate energy from oxygen and 2) generate sugars and lipids from sunlight. In fact, the case could even be made that multicellular life would have never developed without these innovations. If the creation of something monumental like complex life could be kick-started by something like this, why not apply it to other large, pressing “projects” – like say, climate change? 

New research reported in the science news magazine Eos (Soil Fungi May Be a Carbon Pool) calculated that “mycorrhizal fungi take in 13 billion tons of carbon dioxide annually, playing a prominent role in Earth’s carbon cycle.” This is equal to “36% of current fossil fuel emissions.” Perhaps we can scale up this incredible fact of nature and encourage certain carbon reduction strategies to “engulf it,” thus putting an even bigger dent into the amount of carbon affecting the climate of our planet. If we were to do this, it might be helpful to know that certain plants have more mycorrhizal dependence than others. The plant science journal New Phytologist (Mycorrhizal ecology and evolution: the past, the present, and the future) reported that “some plant species, especially those with relatively thick roots rely much more on mycorrhizal fungi than do plants with fine roots, such as grasses.” How to apply these facts in practice would be the collective task for the brilliant minds currently tackling this issue. But regardless of how it plays out, it’s a great example of “horizontally” introducing an already developed ability into a different process that could greatly speed up a solution to a life-or-death problem. 

Finally, adopting a holobiont perspective suggests we must rethink our primal urge to reject the stranger. The Insider/Outsider instinct present in our species (as in many others) ensures the homogeneity of a group, and taken more broadly, an entire culture by viewing with suspicion any persons who do not have intimate, historical, and genetic ties with the larger collective. While this tendency may work well for something small like a wolf pack or a hunter/gatherer tribe of humans, it’s becoming less advantageous in our more fluid, interconnected world. The microbes living in our guts demonstrate that something perceived as “different” can be vital to the overall well-being of a life form and therefore doesn’t need to be rejected. In fact, getting rid of the “offending party” often makes us sick and can even kill us. Similarly, expelling or (more humanely?) forcing individuals, and even entire groups, to conform to the accepted norms and behaviors of a local culture is a big waste of novel skillsets that could potentially enhance the viability of the species. We need “all hands-on deck” to address the current crises putting our planet at risk. We should be desperately seeking novel approaches to solve the unique issues of the moment rather than squashing them due to prejudice and fear.