For the first time ever, scientists observe a doubling in the size of a genome with an immediate evolutionary advantage, solving a longstanding riddle that goes back to Darwin himself, and proving that complexity can arise spontaneously and persist through the generations.
Ever since Charles Darwin published On the Origin of Species on November 24, 1859, some scientists and philosophers have distinguished between two forms of evolution, micro and macro. While the difference can be unclear at times as things in biology often are in an almost infinitely variable world, the underlying principle was simple. Evolution by natural selection might well be capable of producing small, incremental changes to organisms, varying them from their ancestors’ forms, even forming new albeit very closely related species or subspecies, but it cannot create complexity out of thin air, leading to entirely new forms, much less anything as complicated as a human eye. As this thinking went, Darwin himself provided only examples of microevolution in his classic work, either using the breeding of plants and animals throughout human civilization or the slightly differentiated species in remote locations like the Galapagos Archipelago. From there, he extrapolated that small changes like those he catalogued and studied can build up over millennia to produce new adaptations and ultimately entirely new species that bare very little resemblance to their predecessors. Critics of macroevolution agreed with the former – clearly a dog is descended from a wolf, for example – but disagreed with the latter, believing Darwin’s logical leap wasn’t justified and there is some admittedly ill-defined barrier between micro and macro evolution. While the barrier might lack a concrete definition or a clear dividing line, the underlying issue was the origin of complexity. Namely, how could true complexity arise when many of the benefits are only realized after it’s in place? Putting this another way, once an eye exists, its benefits are obvious and it’s no surprise that evolution acts on it in various ways, pushing predator birds to have superior eyesight for example. These benefits might be obvious for 90% of an eye, 80% of an eye, or even 60% of an eye, but what about 40%, 30%, or 20%? According to Darwin’s theory of natural selection, each and every step in the development of the eye or any other complex organ, which in evolutionary terms would likely be measured in fractions of a percent, would need to provide a competitive advantage or the improvement would not be passed down to future generations.
As a result, scientists starting as early as the 1880s began to distinguish between micro and macro evolution, believing Darwin explained the micro side but that a new theory was needed for the macro half of the equation. The Russian biologist Yuri A. Filipchenko was credited with coining the two terms, claiming that Darwin, even coupled with the genetic work of Gregor Mendel which detailed how traits were passed from parents to their offspring, could not explain “the origin of higher systematic units,” meaning the different phylum of animals we observe, arthropods, chordates, etc. and all of the adaptations that make them unique from eyes to gills. In the early 1900s, he wrote, “In this way, modern genetics undoubtedly lifts the veil from the evolution of biotypes…but that evolution of the higher systematic groups, which has always particularly occupied the minds of men (a kind of macroevolution), lies entirely outside its field of vision, and this circumstance seems to us only to emphasize the considerations we have given above about the lack of an inner relationship between genetics and the theory of descent, which is mainly concerned with macroevolution. In such a state of affairs, it must be admitted that the decision of the question depends on the factors of the larger features of evolution, of what we call macroevolution, must occur independently of the results of current genetics. As advantageous as it would be for us to rely on the exact results of genetics in this question, they are, in our opinion, completely useless for this purpose, since the question about the origin of the higher systematic units lies entirely outside the field research area of genetics. As a result, the latter is also an exact science, while the doctrine of descent today, as well as in the 19th century, has a speculative character.”
While the discovery of DNA and the explosion of new research supporting the notion that all life is descended from a single common ancestor has largely shifted the debate in favor of Darwin’s belief that natural selection is the guiding force for even the most complex structures, the macro evolutionists point remained. Where does complexity come from, when it costs so much and the benefits seem to be somewhere in the future? To some extent, the issue was simply brushed aside, operating under the assumption that there must’ve been some hidden benefits at the time which we simply might not be aware of looking back at events that occurred tens or even hundreds of millions of years ago, if not billions in some cases. After all, isn’t being able to see, hear, or smell just a tiny bit better a measurable advantage that, when applied over and over again across a gene pool, will statistically speaking, accrue benefits for survival and reproduction? The numbers don’t lie, and as statistics became more mature along with biology, almost any tiny incremental advantage resulted in models that favored natural selection. At the same time, the discovery of DNA, though it ushered in the golden age of Darwinism, didn’t actually solve the problem. Ironically, it only made the complexity situation more complicated because new adaptations required new DNA. Generally speaking, more complex organisms have more genes and hence DNA than simpler ones, sometimes a lot more. This is true even on a microscopic level, where prokaryotic cells average around 3,000 genes with some as low as 800, but the far more complex eukaryotic cells, the building blocks of all multicellular organisms, range from 19,000 to 25,000, with some as high as 60,000. Clearly, these additional genes and the underlying DNA aren’t accidental, allowing for the complexity associated with macroevolution. You can’t build an eye, an arm, a leg, or anything else without the genes to do so, but where do these genes come from in the first place? Scientists, studying the DNA itself, identified all manner of potential mechanisms, duplications, transcriptions, insertions, and more at the genetic level to explain how DNA can acquire additional information as it is copied in our cells. Correspondingly, they proposed mechanisms where genes can lie dormant and unused in a sort of reservoir that can power evolution in the future. They did not, however, explain how natural selection favors this explosion of genetic information, especially considering all of these new genes and the associated cellular infrastructure comes with a cost in valuable proteins to build and maintain them.
Why favor the doubling of genetic information if the benefit might well be negligible or even at times, in the case of so-called junk DNA, nonexistent? The gulf between prokaryotic and eukaryotic cells is perhaps the best example of this problem. Everyone agrees that once a cell has the genetic information, there is a huge advantage across size, structures, behaviors, and more, but the existence of such a tremendous gulf alone, a more than tripling of the amount of DNA, is hard to explain. Why does nothing lie in the middle with say 6,000, 12,000, or even 18,000 genes on average? If prokaryotic cells managed to survive for over a billion years before eukaryotes arrived on the scene, clearly suggesting that 3,000 genes was more than enough for a self-replicating organism to persist through the eons, why did natural selection suddenly seem to favor an explosion of what appears to be unnecessary complexity at least at first glance? Many ideas have been posited, such as colonies of prokaryotic cells joining together into a single organism, but one could say for sure and certainly, no one had ever seen such a thing in action, either in the real world, in a lab, or even using a simulation. Simultaneously, our ability to run increasingly complex models of evolution, better and better simulations, on increasingly sophisticated computers found similar results. Invariably across these models, complexity was only favored to a point beyond which simpler organisms had an advantage, primarily because they require less resources to build and maintain. The equivalent of the prokaryotes prevailed, outcompeting their more complicated cousins before they became complex enough to be eukaryotes. These and similar experiments only seemed to confirm that the equivalent of prokaryotic cells were enough and that any incremental increase in complexity beyond that would subject the burgeoning replicator to a significant disadvantage. Scientists might well have discovered how DNA can double in size, but not why evolution would favor such a thing in the first place, bringing us back to where we started. While it was rarely stated this way, it seemed all available evidence supported the dichotomy between micro and macroevolution to the point where those who still supported the dichotomy began claiming that scientists had never under any circumstances observed a mutation or other transcription that increased the amount of genetic information available. On the contrary, they insisted the common examples of either natural selection or purposeful breeding were based on deleting genetic information, whether a dog being bred from a wolf or the discovery of a new species of finch on Daphne Major in the Galapagos, rendering macroevolution impossible. While this position might not have been strictly true – indeed I researched it and could not find any definitive information on the matter – proponents of the idea that macro and microevolution were differences of degree rather than kind were ultimately making the same assumption Darwin did, without any real evidence to suggest otherwise, and at least some evidence suggesting that complexity is very, very, very hard to create – perhaps until now.
In a breakthrough experiment, researchers at Georgia Tech observed the complete duplication of a genome, what is known as a “whole-genome duplication” event, a WGP, that remained stable over thousands of subsequent generations, suggesting that it provided an immediate competitive advantage compared to its predecessors with less genetic information. As is frequently the case in science and life in general, the end result wasn’t originally what they were looking for in the first place. “We set out to explore how organisms make the transition to multicellularity, but discovering the role of WGD in this process was completely serendipitous,” explained William Ratcliff, a professor at the school of biological sciences. “This research provides new insights into how WGD can emerge, persist over long periods, and fuel evolutionary innovation. That’s truly exciting.” Starting in 2018, Dr. Ratcliff and his team cultured “snowflake” yeast with the goal of evolving the original subjects into a multicellular organism by only retaining the largest offspring, but while analyzing a sample that was approximately 1,000 days old, Ozan Bozdag, a researcher on the team, found that the yeast had double its number of chromosomes and therefore genetic information, from two to four. The result was so surprising, it was immediately doubted. As we have seen, more complexity doesn’t necessarily provide any advantage right out of the gate and four chromosomes was thought to be fundamentally unstable compared to the usual two. If indeed it arose and persisted, it would be the first time in history anyone had observed it, in the wild, in the lab, or even on a computer. Regardless, when the samples were further analyzed, Kai Tong, a member of the team and a postdoctoral fellow at Boston University, found that the doubling had occurred as early as 50 days, meaning at least in this case, the additional complexity was incredibly stable and was successfully passed down across hundreds if not thousands of generations. The key appears to be the conditions: The experiment favored the growth of larger, longer cells as a pathway to multicellularity, and the doubling of the genetic information offered an immediate competitive advantage in response to this equivalent of selection pressure. In other words, the additional genetic material helped the organism survive, reproduce, and prosper, and it did so immediately.
While we cannot say that the actual evolution of life on Earth followed this pattern, whether there was some equivalent pressure three billion years ago that favored larger cells or a billion years ago that favored multicellular animals, we can now say definitively that, at least in response to certain pressures, more is really more at every step of the way. This might seem relatively minor to the casual observer, but observing a never before seen occurrence, one some doubted in the first place and one which proves at least the possibility that a significant amount of complexity can spontaneously appear as a result of a mutation, complexity that ultimately means humanity could spontaneously appear billions of years later, is no mean feat, especially when the subject is the very origin of life itself.
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