As my colleague, Charissa Terranova, notes in her post for this week, we truly are symbiotes. Bacteria on us and in us contribute to our well being in so many ways. Yes, the staphylococcus currently infecting Charissa’s finger can be classified as a pathogen. And yes, I’m sure Charissa will be happier when these bacteria are eliminated. An “us versus them” attitude toward microbes, however, presents an overly simplistic, and false, binary. Our relationship with microbes is so much more nuanced.
Gut Instinct, our upcoming online exhibition, will allow viewers to consider the importance of our gut microbiota. Increasingly, researchers are revealing important “jobs” played by these intestinal partners of ours. But our relationship with these intestinal partners is only part of the story. As I described in an earlier post, bacterial ancestors reside within every one of our cells. The endosymbiotic theory, first articulated by the evolutionary biologist Lynn Margulis nearly 50 years ago, states that the mitochondria inside the cells of nearly every eukaryote and the chloroplasts inside the photosynthesizing cells of plants originated when previously free-living bacteria invaded or were engulfed by a developing eukaryal cell. Rather than being destroyed, however, these internalized bacteria became essential intracellular organelles.
These specialized intracellular machines certainly represent obvious examples of the intimate relationship between microbes and us. But the extent of our relationship extends well beyond mitochondria and chloroplasts. As Charissa notes, lateral, or horizontal, gene transfer probably has contributed significantly to who we are. We know that bacteria share genetic material via horizontal gene transfer. Genes can move not only between cells of a given species, but also between cells of different species. The story, however, doesn’t end there. Increasing evidence shows that DNA can travel not only between different bacterial species, but also between species in different domains. Our DNA, in other words, may contain bacterial DNA.
And let’s not forget viruses.
During the infection process, some viruses, most notably viruses like HIV in the retrovirus family, insert their genome into our DNA. If this retroviral DNA winds up in a sperm or egg cell, then it can be passed on to future generations. So, what’s our relationship with retroviruses? By some estimates, retroviral DNA may make up nearly 8% of our genome. Perhaps, it exists in our genome merely as junk. Alternatively, it may make us who we are.
Yes, some microbes cause horrific diseases. From the bubonic plague to smallpox to HIV/AIDS, human history is intricately linked with pathogenic microbes. But humans are linked with microbes in a very different ways, too. From the bacteria in our gut to the mitochondria in every one of our cells to our very DNA, microbes make us who we are.
Ouch! My finger hurts! Or, thoughts on symbiogenesis
My finger hurts. The nail bed of the ring finger on my right hand has a staph infection, and while I thought it might be interesting to send my readers off on the winds of imaginations congruent with my next book, I have chosen to keep it focused and the topic near. I will riff on bacteria and the microbiome as it connects back to Gut Instinct, Dave Wessner’s and my exhibition on the gut-brain axis and the interrelationship of the intestinal microbiota and cognition – that goes live online via the SciArt Center’s website in about two weeks! Please stay tuned.
So, I cut my finger while cleaning the house a little over a week ago, and the open splice got infected with the bacteria staphylococcus. There are many kinds of staph: the genus includes up to 40 species. I am not sure which one exactly is giving me trouble, but staph does not always cause problems for organisms. In fact, many of us – all kinds of mammals and birds – host them on our skin and in our mucous membranes on a regular basis. While my finger is a bit out of kilter, our relationship with staph is usually matter of symbiosis. We are often symbionts: two different organisms, living in very close proximity, usually for propitious reasons and under advantageous circumstances.
Which brings me to symbiogenesis.
In the 2002 book, Acquiring Genomes: A Theory of the Origins of Species, Lynn Margulis and Dorion Sagan make the provocative argument that the prime mover of evolution is not random heritable variations arising from mutation over millions of years but symbiogenesis happening laterally and according to acquired inheritance. Symbiogenesis, they explain, is “long-term stable symbiosis that leads to evolutionary change.” (12) By definition, symbiogenesis is the evolutionary theory that eukaryotic cells come from prokaryotes. Margulis and Sagan argue that reframing the focus of evolutionary theory away from mammals, or in addition to the preoccupation with mammals, on microbes (bacteria, prokaryotes) and the unseen world of microbiological “life” reveals evolution and speciation according to a different logic and temporality. Jean Baptiste Lamarck (1744-1829), the French scientist who came up with a theory of evolution just prior to Charles Darwin, “was correct,” they argue. “Acquired traits can be inherited not as traits but as genomes.” (41) Bacteria and other microbes are often busy at work sharing genetic information. “Microbes are champions at passing their DNA to others in the form of entire functional genes.” (41) And this is the root of speciation, they argue.
What does all this mean? How does this impact my work as a humanist?
Traditionally, humanists have cared about the idea and thing called the “individual.” Similarly, the definition of this term has been within the bailiwick of humanism. Margulis and Sagan’s re-inscription of evolution in terms of symbiogenesis – speciation through lateral gene sharing, or what Stefan Helmreich calls “lateral gene transfer,” rather than sex and procreation – introduces a new concept of “life” rooted potentially in the inorganic. In the same vein, the person is never singly “individual” but always already collective – made up of an array of symbionts. As I wrote a few weeks back, we are “super-individuals” instead of “individuals.” The shift from life defined according to sex and procreation, among other forces, to lateral gene transfer has an emancipatory value in that it removes gender-based ideologies long clouding the theory of evolution and related fields, such as behavioral genetics.
I part once again with a refrain, borrowed from Karl Marx and tweaked for symbiogenesis in the present: Symbiotes unite!