Human as Interspecies Community
Discussion
Dorion Sagan:
"Life deals in ... mixed cultures. It has been working with crowds for billions of years. Most of the DNA of the estimated 100 quadrillion cells in our bodies is not “ours,” but belongs to cohabiting bacteria.
Ten percent of our dry weight is bacteria, but there are ten of “their” cells in our body for every one of “ours,” and we cannot make vitamin K or B12 without them. Vernadsky thought of life as an impure, colloidal form of water. What we call “human” also impure, laced with germs. We have met the frenemy, and it is us.
But before leaving this point of the pointillist composition that is our Being made of beings, please notice that even those cells that do not swarm in our guts, on our skin, coming and going, invading pathogenically or aiding probiotically—please notice that even these very central animal cells, the differentiated masses of lung, skin, brain, pancreas, placental and other would be strictly human tissues that belong to our body proper—even they are infiltrated, adulterated, and packed with Lilliputian others. The mitochondria, for example, that reproduce in your muscles when you work out, come from bacteria.
We come messily from a motley. Indeed we literally come from messmates and morphed diseases, organisms that ate and did not digest one another, and organisms that infected one another and killed each other and formed biochemical truces and merged.
Hypersex[1] is a provisional name for the commingling of organisms that meet, eat, engulf, invade, trade genes, acquire genomes, and sometimes permanently merge. Life displays mad hospitality. Korean biologist Kwang Jeon of the University of Tennessee received in the 1970s a batch of amoebae infected with a deadly bacterial strain. Most died. In a set of careful experiments after culturing the survivor amoebae for several generations, he found that the survivors, with fewer bacteria per cell, could no longer live without their infection. Deprived of their new friends and former enemies, the nuclei would not function without micro-injections of bacteria into the cytoplasm. The sickness had become the cure; the pathogens had become organelles; the last had become the first.
Had Jeon, who was a Christian, witnessed speciation in the laboratory? It seems so. But it was not gradual, as neoDarwinism predicts. It was near-instantaneous, the result not of mutations accumulating in a lineage, but of transformative parasitism.
Peculiar behavior, you say? Not really. Considering that life has been growing on Earth for some 3.8 billion years, it is not surprising that life has grown into itself, eaten itself, and merged with itself. Crowd control has long been an issue. Radical solutions have long been the norm. In 2006 researchers at Texas A&M University and the University of Glasgow Veterinary School in Scotland reported to the Proceedings of the National Academy of Sciences that endogenous retroviruses called enJSRVs are essential for attachment of the placenta and therefore pregnancy in sheep.
Like bacteria, viruses “R” us: They have moved in to our genomes. Viral structural proteins have been “hijacked” and integrated into mammal reproductive tissues, immune systems, and brains. Some retroviruses disable receptors that lead to infection by other retroviruses. There is no racial, let alone genetic purity in life. At bottom we are part virus, the offspring not just of our parents but of promiscuous pieces of DNA and RNA. The road to humanity is paved with genetic indiscretions and transgressions, no less than sheep would not be sheep without their acquired enJSRV.
Biologist Margaret McFall-Ngai (2011), asked a roomful of doctors what it meant for our marine ancestors to be surrounded by all those germs—about a hundred million cells per liter. They had no answer, but she told them: She has proposed that the immune system evolved not to eliminate pathogens but to select for symbionts in the microbe-packed waters of our metazoan ancestors. The immune system in its origin may thus be more like an employment agency, recruiting desired species, than like a national security state, recognizing and refusing entry to guard the fake purity of the Self.
Today it is widely recognized that the cells of animals were once a wild party of two if not three ancient bacteria: the oxygen-poisoned archaebacteria host, the oxygen-using bacteria that became mitochondria, and perhaps wildly squirming spirochetes, which abound in anaerobic environments. These wrigglers often penetrate their fellows, which have no immune systems. They feed at the edges, becoming snaky motors propelling their brethren, or take up residence inside them, wiggling happily ever after.
According to my mother, who’s been right before (Teresi 2011), ancient bacterial symbioses gave our ancestors the intracellular motility abilities we see in mitosis, and in the growth of undulating appendages.
The creation of new symbioses by mergers on a crowded planet is called symbiogenesis. Although this type of evolution sounds bizarre—a monstrous breach of Platonic etiquette in favor of polymorphous perversity—it is now confirmed by genetic evidence, taught in textbooks. It is a fact, or what Bruno Latour and Isabelle Stengers, not putting too fine a point on it, would call a factish. Nonetheless, although symbiogenesis—the evolution of new species by symbiosis—is now recognized, it is still treated often treated as marginal, applicable to our remote ancestors but not relevant to present-day core evolutionary processes.
This is debatable. We are crisscrossed and cohabited by stranger beings, intimate visitors who affect our behavior, appreciate our warmth, and are in no rush to leave. Like all visible life forms, we are composites. Near unconditional hospitality is necessary when we consider the sick factish that most of the human genome may be viral DNA (Carter 2010). Some partnerships are fantastic. Luminous bacteria cram together to provide various marine animals with organs to light their way; deep-sea angler females even use their shiny bacteria lights as lures to catch other fish. Luminescent bacteria, of the species Vibrio fischeri, provide the bobtailed squid, Euprymna scolopes, a nocturnal animal which feeds in the moonlight, so-called “counter-illumination”: it projects light downward from its light organ, so it doesn’t show up as a tasty morsel outlined in silhouette for hungry predatory fish below.
Nestled within the chromosomes of some parasitic wasps lie bacteria. Multiple insect species transform gender due to Wolbachia bacteria. The genus is nearly ubiquitous in insect tissues. By disabling the gender-changing bacteria, antibiotics can make separate species of jewel wasps interbreed again. More bizarre than the space aliens we imagine abducting and toying with us on their saucers, these gender-changing bacteria bring in suites of genes for metabolic and reproductive features as they establish symbioses, often permanent, in arthropods." (http://culanth.org/?q=node/513)
Source
- Article: Dorion Sagan. The Human is More than Human: Interspecies Communities and the New Facts of Life.