Here we are, the world-dominating Hominin, miserably in thrall to the tiniest and simplest form of life, a virus. It’s not even alive in some opinions, depending on your definition of Life. We learn the things that Life must be capable of, all of it contributing to that overarching requirement, reproduction. A virus can do none of this alone and needs to find and enslave a living cell, and we are currently well aware of how well that can work.
So what does constitute ‘living’ ?
Once the earliest organic molecules grouped and self-assembled into something that could get energy from its environment so as to assemble some more organic molecules, probably inside a fatty membrane, the process was started. Inevitably the faster the assembly and the more efficient the energy-grab, the more ‘descendants’ the microscopic blob would have, so the most efficient type would become the most common, hence the dawn of natural selection. If it undergoes Darwinian evolution, it’s alive. As COVID 19 itself demonstrates only too clearly, it’s alive.
Since its beginning over 4 billion years ago, Earth life has continued to include vast amounts of its earliest triumph, bacteria, but increasingly bigger and more complex organisms culminating (we like to think) in mammals such as ourselves. Even bacteria are intricate super-structures compared with a virus: bacteria are little cells and suffer from their own virus parasites. So much so that these “bacteriophage” viruses can be used medically to combat bacterial infection. The technique was developed in the Soviet Union from 1920, but with cheap access to powerful antibiotics after the Second World War was eclipsed. Now surging antibiotic resistance has prompted renewed interest in bacteriophage therapy.
Occasionally one of these hidden genetic invaders even gets silently inherited, generation to generation.
Whether they are the ultimate retrograde parasites, stripped-down cells reduced to a fraction of an earlier size, or weird survivors of earliest Earthlife – those pre-cellular blobs – is currently debated. Either way, there are now viruses everywhere. Each virus type has preferred hosts, and every animal, plant and fungus has its virus invaders that can hijack and kill its cells. Shingles, HIV and cold sores remind us that a few can infect and ‘hide’, then break out again long after the host’s recovery. They do this by inserting their genetic material right inside the much larger chromosomes of the host cell, and evade detection. Occasionally one of these hidden genetic invaders even gets silently inherited, generation to generation. Nasty!
Supposing 150 million years ago the vagaries of evolution arrived at a small whiskery animal that carried its babies inside the mother’s body, safe from marauding dinosaurs. The embryos kept warm but the primitive placenta that fixed them was not a fast highway for nutrients. You might wish for a new gene that facilitated nutrient transfer, mother to embryo. Supposing an ancient virus infected that ancestral mammal, pushing through membranes into her body cells and reproducing destructively. She recovered, but it stayed, hidden in her chromosomes, eventually inherited down through her descendants over more than 50 million years of mammal evolution. The virus-derived gene became gradually altered and rendered harmless, a ‘domesticated’ version; shelved in fact.
As years went on the mammals diverged, and the lines to the cattle, carnivores, Old World monkeys, apes plus humans, rodents, and rabbits plus hares, all kept versions of that original viral gene. Their placentas variously evolved but each lacked the modern closeness between mother’s blood and embryo. A gene that could achieve that ‘fusogenic’ function, would have been an advantage. And they each had one! Now ‘domesticated’, ready to be re-purposed and newly expressed alongside other placenta-building genes.
You see where this is going ?
By about 30 million years ago those mammals had cellular fusion linking mother and embryo.
It comes with a jolt to read the genetic evidence that the ancestral gene for a key placenta function today came from an ancient viral infection. Despite all the aeons of erosion, its virus-like features are still recognisable through detailed genetic analysis. A virus hijacker that long ago came to pierce and kill, now tamed and harmless, promotes nutrient transfer from mother to embryo, generation to generation. The protein it produces to breach cell membranes is called Syncytin. Placenta function is not the only animal feature known to benefit from co-opted virus genes, but it’s the most famous.
See :- Paleovirology of ‘syncytins’, retroviral env genes exapted for a role in placentation Christian Lavialle, Guillaume Cornelis, Anne Dupressoir, Cécile Esnault, Odile Heidmann, and Thierry Heidnann Philos Trans R Soc Lond B Biol Sci. 2013 Sep 19; 368(1626): 20120507. doi: 10.1098/rstb.2012.0507
None of this detracts from our loathing of coronavirusSARS-CoV-2, that causes COVID-19. That’s a very different class of virus from the ancestor of the Syncytingene, with very little similarity. Coronaviruses are strikingly younger, the estimated origin of the earliest coronavirus being about 10,000 years ago, whereas the Syncytin ancestor dates back over 30 million years. We should be eager for clever vaccines to combat current virus diseases such as influenza, mumps, measles, rubella, ebola, HIV, rabies, common cold, polio, chickenpox, hepatitis, herpes infections, SARS, MERS, and currently, above all, COVID-19, caused by coronavirus SARS-CoV-2.
Yes, there are some species that Earthlife could happily do without.
Good health to Everyone!
By Dr Valerie Jeffries