Scientists discover a new cell that lives like a virus and a new rule of life that can best be seen as the opposite of a regular rule, introducing chaos into the operation of a cell at a fundamental level.
Scientists like tidy groupings, where you are either in or you’re out. At least since Sir Isaac Newton revolutionized our understanding of the world by positing three inviolable laws of motion and using them to explain the gravitational force, most scientists have aspired to describe reality with mathematical equations, positing laws that are essentially formalized groupings of forces and objects, and testing them against experience. To a large extent, the goal of these laws is to predict the future. When you apply one of Newton’s theories, you are describing what will happen or what has happened, sometimes down to an incredible number of decimal points. In many ways, particularly in physics, chemistry, and other so-called hard sciences, the scientific establishment has been very successful in this regard. We know far more about the world than we did in the 18th century, and can predict a wide range of outcomes with an insane level of precision, from when the sun will rise in the morning to how radioactive plutonium will behave in a nuclear reactor. Of course, this doesn’t mean there haven’t been surprises, unexpected discoveries that challenged our assumptions, from the inflationary universe to dark matter and dark energy, suggesting that even when we think we know something for certain, the universe frequently presents more questions than answers. Perhaps nowhere is this more apparent than in biology, where a century and half after Charles Darwin proposed how animals evolve due to natural selection, the natural world continues to defy easy description or explanation to the point where forget predicting what we might discover in the future, we can’t even definitively say whether something is dead or alive in the present. In fact, scientists discovered a new type of cell that challenges our current assumptions in this regard as recently as last month, upending decades of conventional wisdom in the process. It has long been assumed that cells are living things, but viruses are not, creating what seemed to be a pretty solid dividing line between living and unliving. This dichotomy was based on whether or not the microorganism in question has a metabolism and whether or not it can reproduce on its own. Cells, or at least all cells we were aware of until now, carry out internal functions on an ongoing basis to maintain their existence. This includes things like ensuring structural integrity, repairing damage, absorbing nutrients, expelling waste, etc. If these processes are interrupted or fail for any reason, the cell dies. Cells reproduce themselves by splitting in two, a process called mitosis that requires no third party to complete. Viruses, in contrast, do not perform any ongoing functions or reproduce themselves directly. Instead, they reproduce by relying on a living cell to build copies based on provided instructions. Otherwise, they are completely inert, do not repair or maintain their bodies in any way, making them essentially a microscopic sack of RNA (or DNA in some cases), until they encounter a living cell.
This line between living and unliving appeared to hold true until Dalhousie University genomicist Ryo Harada and his colleagues found something completely unexpected deep inside a tiny piece of plankton. While cataloging the DNA of Citharistes regius they discovered an even tinier cell, dubbed Sukunaarchaeum, which does not appear to have any metabolism at all, relying on its host for all of those functions, but that can reproduce on its own, representing something halfway between what was considered a normal cell and a virus. “Its genome is profoundly stripped-down, lacking virtually all recognizable metabolic pathways, and primarily encoding the machinery for its replicative core,” Dr. Harada and his team explained. “This suggests an unprecedented level of metabolic dependence on a host, a condition that challenges the functional distinctions between minimal cellular life and viruses.” Not surprisingly, its genetic code is incredibly simple even compared to viruses, containing only 238,000 base pairs versus between 735,000 and 2.5 million, making it the simplest cell ever encountered, and yet, based a preliminary analysis of Sukunaarchaeum’s DNA, it truly is a cell, belonging to the Archaea domain of organisms, which ultimately gave birth to all modern cells, making it a distant ancestor of what makes up our own bodies. The circular structure of the chromosome even resembles modern bacteria. “Sukunaarchaeum may represent the closest cellular entity discovered to date that approaches a viral strategy of existence,” the researchers wrote. “This extreme specialization… challenges our fundamental understanding of the minimal requirements for cellular life.” To say this was unexpected is an understatement. No one thought the discovery of a tiny organism hidden in a tiny organism would shatter our perceptions of what it means to be living or unliving; an organism that behaves to a large extent like a virus, adopting its lifestyle and lack of metabolism, but which belongs to another domain entirely. At the same time, perhaps we should have been. It was only last year that famed evolutionary biologist Richard Dawkins advanced a new paradigm which holds that all life on earth is essentially a collection of viruses traveling through time. The difference is in how they travel. Either vertically, as in together from generation to generation along with the overall organisms’ reproduction, or horizontally, as in hopping from organism to organism on their own. If they travel vertically, we should expect even parasites to positively or at least not negatively impact their hosts, exhibiting a high degree of cooperation for shared survival and reproduction. If they travel horizontally, we should expect disease if not death. Given Sukunaarchaeum appears to travel vertically, living and reproducing inside the host, it doesn’t manifest any destructive tendencies that we can see so far, though it doesn’t seem to have any net benefits like the bacteria in our gut. Either way, discoveries like this represent an opportunity to probe Dr. Dawkins’ bold idea in a way perhaps even he didn’t foresee.
The second unexpected discovery wasn’t related to a particular organism, but rather a general principle or rule of life. Previously, scientists have identified around two dozen of these principles that – while not the equivalent of the laws of physics in their precision, nor nearly as predictive – have proven valuable in understanding how life works on this planet. Two examples include Allen’s Law which correlates body shape in warm blooded animals to climatic conditions, usually yielding short and stocky phenotypes in cold areas compared to tall and lanky in warm areas. Bergmann’s Rule similarly finds that vertebrates in colder climates tend to be larger than warmer ones; the root cause of this is believed to be the ratio between surface area and volume, where less surface area compared to volume in colder areas conserves heat. The new rule, however, is a bit different and a bit more radical. In fact, it might best be understood as the opposite of a traditional rule. According to the University of Southern California, life takes advantage of what they call “selectively advantageous instability,” or SAI, which holds that a certain amount of chaos is required for living beings to thrive. In this case, the instability is found in proteins and even entire genes which regularly degrade and rebuild in a way that is helpful to the functioning of the overall cell for a certain period even at the expense of its own survival. “Even the simplest cells contain proteases and nucleases and regularly degrade and replace their proteins and RNAs, indicating that SAI is essential for life,” USC molecular biologist John Towers said in a press statement. “This can favor the maintenance of both a normal gene and a gene mutation in the same cell population, if the normal gene is favorable in one cell state and the gene mutation is favorable in the other cell state.” The result is greater genetic diversity, which appears to make organisms more adaptable even when it favors a shorter lifespan for the cell or the organism as a whole, potentially causing both aging and disease. Degrading cells can mutate, leading to sickness and death like cancer. “Aging has proven to be difficult to define, but most definitions include an increased chance of death with age, and decreased reproductive fitness with age,” the research paper read. “SAI can create a cost for the replicator in terms of energy and/or materials, and this cost might be interpreted in terms of promoting aging.”
Regardless, this discovery, radical as it may sound, should probably not be surprising for two reasons. First, evolution might appear to function at the level of the individual organism reproducing itself through the ages, but it actually occurs at the level of the individual gene, both vertically and horizontally according to Dr. Dawkins. This means that the gene itself doesn’t care what happens to the organism, so long as it is continually reproduced. Therefore, processes that benefit the reproductive success of the gene at the expense of the health of the individual will ultimately be favored. Second, scientists have long believed that the process of evolution itself is evolvable and that certain sets of genes, biological structures, processes, etc. have been selected because they are extremely adaptable. While Dr. Dawkins’ recently asserted that DNA can be seen as a model of an organism’s past history as each species makes a bet that the future will be similar to the conditions of their ancestors, change is a constant part of the natural world. Organisms that can rapidly respond to changes in the environment and other factors are more likely to adapt over time, and hence the lifeforms that dominate the world today have been flexible enough to keep pace with everything from snowball earths to asteroid impacts. Most life on earth can be traced back to an ancestor that arose during the Cambrian Explosion, almost 550 million years ago. DNA that evolved then is in your body right now, much of it shared with every living creature, from humans to fruit flies. Though many species have perished, the animals that arose during that period developed forms and modes of existence that have persisted for hundreds of millions of years in many cases because they could respond to the unexpected, quickly and effectively. SAI, on the surface at least, seems to capture that essential element at a cellular level and should be studied further in that light, offering insight into both why modern life forms are the way they are and how those forms have persisted for such an incredible period. Either way, Hamlet had it correct when he told Horatio that there are more things in heaven and Earth than are dreamt of in our philosophy, though perhaps some of that continues to be our own misunderstandings rather than reality. We like things in their own little boxes and not just scientists. The world is a whole lot messier, but in many cases what seems surprising in the moment makes sense in retrospect. With all the wonder and strangeness of life on Earth, why wouldn’t we expect there to a cell that lives like a virus? Is it really so strange? More fundamentally, how can this wonder and strangeness be achieved without a certain amount of chaos?
Confessions of a Conservative Atheist 