Sunday, November 19, 2017

The Demeaning of Life...Chapter 3. Evolutionary Theory and the Modern Synthesis

Now one could say, at the risk of some superficiality, that there exist principally two types of scientists. The ones, and they are rare, wish to understand the world, to know nature; the others, much more frequent, wish to explain it. The first are searching for truth, often with the knowledge that they will not attain it; the second strive for plausibility, for the achievement of an intellectually consistent, and hence successful, view of the world. To the ones, nature reveals itself in lyrical intensity, to the others in logical clarity, and they are the masters of the world.
                          Erwin Chargaff, Preface to a Grammar of Biology (1971)
An important corollary of Natural Design is that modern evolutionary theory is lacking in key regards, contrary to the widespread belief that our understanding of evolution is now complete in all but its finest details. This is not the case; Darwin himself had no idea how complex and multifaceted the matter was and key parts of his theory, long admired and cherished for their elegant simplicity and indisputable truth, have over time evolved and undergone adaptation. For instance, the role of natural selection—the most fundamental aspect of Darwin’s theory—is being revisited and its status as evolution’s primary driver called into question. (It is now accepted belief that several factors are at work, each of which is subject to selective pressures.) As well, by the time Darwin’s ideas had gained widespread acceptance, no one had yet given serious thought to the evolution of physiological processes and systems. Complex biomolecules such as DNA, unknown at the time, also have evolutionary histories. Natural Design offers a new angle on such matters. 
Before tackling these convoluted topics, a historical overview of how modern evolutionary theory took shape will provide useful perspective. This will be followed by a look into scientific materialism—a stance based on the assumption that all phenomena are solely the result of physical (“material”) matter being acted on by natural laws, nothing more—and how this approach became the basis for all scientific methodology. Again, this is pertinent to the Natural Design viewpoint. 
The two bedrock assumptions that Darwin’s theory of evolution by natural selection is founded on are that there can be random variations in genetic material (mutations) which can lead to adaptations that in turn might improve an organism’s chances of survival. The late paleontologist and evolutionary biologist Stephen Jay Gould, summarizing its main tenets: “First, that all organisms produce more offspring than can possibly survive; second, that all organisms within a species vary, one from the other; third, that at least some of this variation is inherited by offspring. From these three facts, we infer the principal of natural selection: since only some of the offspring can survive, on average the survivors will be those variants that, by good fortune, are better adapted to changing local environments. Since these offspring will inherit the favorable variations of their parents, organisms of the next generation will, on average, become better adapted to local conditions.”  
During the two decades Charles Darwin spent working out his ground-breaking theory, neither he nor any of his peers had any idea how unimaginably complex the manifold workings of life actually were. As an illustration of how little was understood it that era: German biologist Ernst Haeckel, a contemporary and great admirer of Darwin’s, believed that the cell (still a little-known entity) was “not composed of any organs at all, but consist[ed] entirely of shapeless, simple, homogeneous matter…nothing more than a shapeless, mobile, little lump of mucus or slime….”
While Darwin was slowly and meticulously refining his ideas following the voyage of the Beagle, a congenial and self-effacing Austrian friar was growing pea plants in his abbey’s garden. Over the course of eight years, Gregor Mendel patiently reared almost 30,000 plants while piecing together the foundation of modern genetics.[1
Due to a number of adverse historical circumstances, Mendel’s far-reaching insights went unrecognized for nearly half a century. Significantly, after all his painstaking labor and meticulous recording of data, the priest’s findings were made known solely through two public lectures followed by a paper submitted to the Proceedings of the Natural Science Society of Brünn. Aside from that one obscure 1866 publication, Mendel personally distributed 40 reprints of the treatise to suitable people and…his seminal research quickly all but disappeared. It was ignored by fellow botanists, who found themselves confused about the object of it all. They perceived the work as being merely about hybridization (animal breeding and horticulture being a feature of their day-to-day lives), and were put off by Mendel’s perplexing reliance on numbers. While this might seem odd today, scientifically rigorous experimentation involving statistics was a foreign concept to biologists of that era.
Mendel’s efforts were largely forgotten until 1900, when three European plant physiologists, independently performing similar experiments, simultaneously brought to light the friar’s enormous contribution to science. Mendel’s treatise Experiments with Plant Hybrids had been published seven years after the first edition of On the Origin of Species came out but, despite an apocryphal story that Darwin owned a copy but never read it, there is no evidence he was aware of the work.[2] (Many scholars believe that Darwin, whose mathematical skills were poor, in all likelihood would not have recognized its implications.) Mendel, long in poor health, died at only sixty-one. All his papers, all his scrupulous documentation, were carted out to a hill behind the abbey shortly after his death and unceremoniously burned.[3]  
Once brought to light, Mendel’s ideas rapidly gained traction. Early geneticists debated a growing number of conflicts with Darwinian precepts. These were based in part on the realization that Mendel’s laws had shown that inheritence was a material affair that could be tested by experiment, not the result of Darwin’s more abstract and somewhat nebulous selective process. Many believed that traits were inherited in the form of discrete units, which could be accounted for by the newly discovered phenomenon of mutation (rather than a measured blending as called for by natural selection).
The discovery of genes as “particulate” units of inheritance had a huge effect on accelerating evolutionary research. In the 1920s and 30s, following the acceptance of chromosome theory, a new discipline emerged: population genetics (the study, heavy on statistical analysis, of how traits arise and move through populations). Thanks largely to work by two Britons—statistician Ronald Fischer and biologist J.B.S. Haldane—and American geneticist Sewall Wright, Mendelian genetics and the concept of evolution by natural selection were finally integrated: a unification that became feasible only after it was finally recognized that the gradual, steady modification central to Darwin’s theory was entirely compatible with Mendel’s axioms. This paved a way to resolve various disputes that had been intensifying for some time.
These conflicts were for the most part put to rest during the course of an international symposium held at Princeton in 1947, shortly after WW II’s travel restrictions had lifted. It became known as the modern Darwinian synthesis. The synthesis was basically a set of ideas that were assertively championed by bird taxonomist-cum-evolutionary biologist Ernst Mayr and several of his chief collaborators in America, notably paleontologist George Gaylord Simpson, expatriate Soviet  geneticist Theodosius Dobzhansky, and botanist G. Ledyard Stebbins—all prominent experts in their fields. In England, well-known biologist and science popularizer Julian Huxley (grandson of Thomas, “Darwin’s bulldog) used his public visibility to spread the word, in particular in promoting his vision of human progress through evolution.
Up until that time, researchers working in disciplines such as paleontology,    systematics, and natural history were neither in close communication nor sharing their findings. To some extent, these areas were all influenced by Darwinian theory (even though many of his ideas had long since fallen out of favor). The specific disciplines’ views on evolutionary agencies and their relative importance had diverged; each was starting to attribute different meanings to established concepts and use different terminology to describe them. Some had even formed their own evolutionary theories. Population-level thinking had not yet taken hold. Of even greater concern, paleontologists were actually at odds with the concept of natural selection—a consequence of not seeing the gradual changes required by its precepts reflected in their established fossil records. Those working with population genetics were convinced they had finally found a way to connect the different disciplines.
The symposium, considered a great success, united many branches of biology under one common evolutionary umbrella that (according to Gould) “validated natural selection as a powerful causative agent and raised it from a former status as one of a contender among many to a central position among mechanisms of change.” This had been the gathering’s intended goal. Mayr made clear that the intention of the synthesis was no less than a means to designate the general acceptance of two conclusions: gradual evolution can be explained in terms of small genetic changes (‘mutations’) and recombination, and the ordering of this genetic variation by natural selection; and the observed evolutionary phenomena, particularly macroevolutionary processes and speciation, can be explained in a manner that is consistent with known genetic mechanisms.”
The true significance and influence of natural selection was still being debated until Dobzhansky reaffirmed its primacy with the publication of his book Genetics and the Origin of Species in 1937—a critical, solidifying event in the movement’s early development.[4] The alliance thereafter commonly became known as “the synthesis” (although, in time it became known—somewhat erroneously—as neo-Darwinism.[5]) However, like Darwin and his contemporaries, Mayr and his esteemed colleagues had little notion of the real complexities lying beneath the surface of their various disciplines. Microbiology was in its infancy and the helical structure of DNA was yet to be revealed. No botanists ecologists, or embryologists had attended the symposium and new findings in those fields and others would muddy the water for years to come.
Due in part to the strong personalities and fervor of neo-Darwinism’s promoters, from its outset the movement was infused with a zealousness that made it notably resistant to change—an ironic misfortune, since all the scientific branches concerned were in flux. By the 1950s the movement started to move away from the pluralism of the 1930s and 40s in favor of an almost complete emphasis on adaptationism (the view that many traits are the result of evolution through natural selection). The synthesis entered a phase of intellectual rigidity—what Gould later christened “the hardening.” What had set out as a collaborative integration began to exclude and marginalize.
The following decades witnessed a flood of new information and ideas, some of which received a great deal of resistance. Only fifty years later, leading experts became increasingly aware that the modern synthesis was in serious need of modernization. While it has taken time, it is now becoming widely recognized that evolutionary theory is a considerably less straightforward matter than was previously assumed, with problematic questions still surfacing. For one thing, we now know that natural selection is but one of a number of influences driving the whole process. Also, during this same period there has been a parallel broadening of perspective with regard to the evolutionary aspects of all branches of biology. Thanks to the arcane strangeness of quantum theory, a growing understanding of the microscopic realm, and the newly revealed universe of the cell, we have arrived at a more sophisticated appreciation of nature’s subtleties and complexities. The entire framework of the way we view life has shifted. But it remains a work in progress.  

     ©2017 Tim Forsell                               19 Nov 2017

[1] Properly speaking, Mendel was from Moravia, a historic region in what is now the Czech Republic. Many misconceptions surround Mendel and his work: for one, he was a friar—not a monk—and  lived not at a monastery but at an abbey, among a community of very talented and learned men. (Moravia, in the early 1800s, was ahead of its time in promoting the power of science in order to improve social and economic conditions and was a region known for its advanced animal breeding and horticulture.) Another thing: it was a happy coincidence that Mendel chose to work with pea plants. He had no way of knowing that the traits he chose to follow were controlled by genes found on different chromosomes and those traits also happened to denote distinct, unambiguous features not typically displayed in such regular fashion.
[2] Mendel and his peers were well-acquainted with Darwin’s work. (Mendel had a well-worn copy of Origin.)
[3] The complicated story of the simultaneous “rediscovery” of Mendel’s research is somewhat out of the scope of this work but quite intriguing. Mendel’s obscure publication had been passed around by a few plant breeders. Among those who had read the paper were Dutchman Hugo de Vries, German Carl Correns, and Austrian Erich von Tschermak. Working independently, each achieved in their own experiments results similar to Mendel’s. Correns barely missed out on beating de Vries to publication and there is evidence that both intended to claim discovery of what became known as Mendel’s Law (the 3:1 ratio of dominant versus recessive characteristics generated by the hybridization of two purebred strains). Coincidently, de Vries sent Correns a copy of his newly published article, written for a French journal, that made no mention of Mendel. Correns was just then putting the last touches on his own manuscript and, bitter at having been upstaged, hurriedly finished his own paper and sent it to the German Botanical Society for publication. Correns made a point of crediting Mendel with the 3:1 law’s discovery to undercut de Vries’ claim to priority; whether or not he intended to do the same is still debated. But, unbeknownst to       Correns, de Vries had already sent his paper to the German Botanical Society and, in this version, had credited Mendel. Thus was Mendel’s work rediscovered and handed over to science.
[4] Dobzhansky was the first geneticist to work in the field with natural populations. He “helped to establish population genetics as the empirical field that provided the long-missing piece to the original Darwinian puzzle.” 
[5] George Romanes, a protégé of Darwin’s, “coined the term neo-Darwinism to refer to the version of evolution advocated by Alfred Russell Wallace and August Weismann with its heavy dependence on natural selection…[rejecting] the Lamarckian idea of inheritance of acquired characteristics” (a commonly held notion of the era that Darwin himself had embraced).

Sunday, November 12, 2017

The Demeaning of Life...Chapter 2: Miracle Molecule

I’m re-posting chapters of my work-in-progress, The Demeaning of Life. Last winter, I did major re-writes and rearranged the order of a number of chapters. This one, about DNA, has not been significantly altered but I’m posting it again for the sake of continuity. Plus, it’s one of the most compelling accounts in the whole book. Read this, and the world will never look quite the same….

That morning, Watson and Crick knew, although still in mind only, the entire structure: it had emerged from the shadow of billions of years, absolute and simple, and was seen and understood for the first time. Twenty angstrom units in diameter, seventy billionths of an inch. Two chains twining coaxially…one up the other down, a complete turn of the screw in 34 angstroms. The bases flat in their pairs in the middle… a tenth of a revolution separating a pair from the one above or below…one groove up the outside narrow, the other wide. A melody for the eye of the intellect, with not a note wasted.
Horace Judson, The Eighth Day of Creation

Few things could better express this tendency of jadedness toward the natural world than how people regard DNA…and the entire subject of genetic inheritance.
Most people are at least vaguely aware of what DNA is; any high school student who has taken Biology 1A knows the gist of its story. College students learn a somewhat deeper account, still very much abbreviated. As for the entirety of the famed double helix’s astoundingly elaborate narrative: among geneticists and molecular biologists (even including educators in those fields), probably only a few are intimate with their area of interest down to its finest minutiae. Meanwhile, a multitude of able researchers resolutely work toward a goal of piecing together the final details and filling in a few gaps.
 Less than fifty years passed between the discovery of DNA and completion of the Human Genome Project—largest collaborative biological study in history. This colossal undertaking, bearing so much promise, fell short of generating the world-wide enthusiasm resulting from DNA’s discovery, despite plenty of media hoopla. Yes, times have changed, but it leaves me cold whenever I encounter this strange, distinctly blasé attitude (conveyed in speech or print) when the subject of “the miracle molecule” comes up. And what this has to say about our conception of life, our collective lack of imagination. No doubt this is partly the result of a shared cultural ennui together with DNA’s profound—even alien—nature. Some people profess to believe it is “just a chemical,”[1] just another molecule, albeit a very large one with some singular characteristics. Although DNA actually is just a chemical, nothing else is even remotely in its class. And not just in the realm of chemistry: nothing at all. DNA is absolutely beyond compare.
A quick review is in order. Prepare to be astonished.
Deoxyribonucleic acid, perhaps nature’s greatest innovation, is truly ancient. While almost universally assumed to have arisen from simpler precursors, DNA has likely changed hardly at all since life’s earliest days, so impeccably is it suited for its all-important role. Earth’s surface has been repeatedly transfigured, continents have come and gone, while this strange substance has persevered. Nothing on Earth has remained unaltered for anywhere near as long. Every individual molecule is uniquely different but identical forms of DNA reside inside every cell of all known organisms, with few exceptions.[2] Each strand has ties with the original in one unbroken hereditary chain. Though seldom acknowledged, DNA’s antiquity and continuity are statements of    tremendous import that color life’s entire story. 
The molecule is shaped like a continually twisting ladder composed of two  complementary strands. Both strands are uninterrupted chains of modular subunits known as nucleotides, each of which consists of a linked phosphate (PO) and ribose (a sugar, CHO) attached to another component called a base. Every nucleotide’s phosphate–ribose components form unvarying, identical subunits joined end-to-end to fashion the molecule’s two backbones (the ladder’s upright members). The base components, however, come in four varieties. Small, fairly simple molecules, they line each nucleotide chain in a variable sequence. The bases lie between the backbones, one from each side joined in the center by hydrogen bonds,[3] forming base pairs. In the ladder analogy, these pairings represent the rungs and their shapes and arrangement impart DNA’s twining configuration. Of critical importance: of the four bases (their chemical names by custom abbreviated T, A, C, and G), T can bind only with A, C only with G.
These bases, each with unique identities, comprise a four-letter genetic “alphabet” from which the genetic code is derived. (Genes are sequences of these “letters”[4] that are transcribed into coded instructions used to assemble ornately structured proteins—an exceptionally important class of molecules which, among their many roles, act as machines that perform a multitude of vital tasks.[5]) The two strands are complementary; during mitosis (the process of cellular division) they are physically separated and each half is used as a template to make a replica of the other.
Thus, once reconstructed, there are two copies (both identical to the original) and each daughter cell receives one. This is how genetic information is passed on; each cell bears all the information needed to construct an entire organism but most of that information is either never used or is “switched off” when not needed. In eukaryotes—life forms whose cells possess a membrane-bound nucleus where all genetic material resides—DNA is bundled into a number of discrete, paired packages called chromosomes. But in the unicellular prokaryotes (organisms such as bacteria) just one or two circular chromosomes float freely through each individual’s watery interior.
 Human cells each have 23 pairs of chromosomes (one set from both parents) for a  total of 46; the different pairs vary considerably in size depending on the quantities of DNA they contain. Also: different types of organisms have different numbers of chromosomes—a figure that can vary a great deal even in similar groups, with no obvious pattern. (For instance, the number in a single genus of ant, Myrmecia, ranges between two and 84 depending on the species.)
Consider these curious facts: In humans, if all the DNA contained in just one cell’s 46 chromosomes (by some estimates comprising around 200 billion atoms[6]) were stretched out and laid end-to-end to form a single strand, though only ten atoms wide it would be almost six feet long. In our bodies, each cell’s set of chromosomes contains an estimated 3 billion DNA nucleotide “letters”—all this compactly stored in its nucleus. Our bodies contain around 30 trillion cells, a figure that amounts to roughly 450 times Earth’s current human population.[7] Thus: if all one’s personal DNA were drawn out and laid end-to-end it would wrap around the equator [Drum roll, please!] well over one…million…times. Ladies and gentlemen! Pause for a moment and try to consider what these weird and wonderful things might signify. Keep in mind: all that DNA fits inside your body. It is inside you right now.
Normally, chromosomes are loose in the nucleus in the form of slender threads made up of the actual DNA molecules wrapped around spool-like structures called histones. These bundles are coiled tightly into chromatin fibers which, for the most part, float freely but are attached at many points to the nuclear membrane’s inner surface.  However, prior to replication they have to be isolated and further compacted. No simple matter, this is accomplished with the aid of an army of protein helper molecules. (Amazingly, there are some 4000 specific types of these assistants.) The cobweb-like array is detached from the nuclear membrane and the chromosomes twisted into tight coils. These twist into tight coils that coil yet again, resulting in a dense clump of genetic material. After replication and division, the process is reversed and the new chromosomes are unwound. But, before the chromosomes briefly take on their so-called “condensed” form (the plump “X” shape people are most familiar with) they have to be replicated.
The duplication process is staggering in its complexity and exacting coordination. Prior to mitosis the chromatin fibers are unwound, making them accessible to swarms of replicating enzymes. (Enzymes are special protein molecules that assist with reactions; more about them shortly.) There are numerous replication sites on each chromosome and the DNA is duplicated in short stretches that are detached and later rejoined. Replisomes, complexes of various protein machines involved with the duplication of the two strands after separation, work in paired teams. Around 100 pairs seize specific places on their chromosome and begin working in opposite directions, churning out new strands at the rate of 50 nucleotides per second. Each of the chromosomes are duplicated simultaneously; with thousands of replisomes operating throughout the nucleus, all the cell’s DNA can be replicated in about an hour.
A family of more than 30 types of enzymes is involved: helicases separate the two strands; DNA polymerases gather free-ranging nucleotides and place them in position. Topoisomerases “relax” the tightly coiled DNA and one type, gyrase, keeps the twisting strands from becoming hopelessly tangled by temporarily breaking them and allowing the kinks to unwind before rejoining them. While the two halves are divided they are highly reactive; to prevent them from being chemically attacked or re-attaching prematurely, single-strand binding proteins are called up to temporarily cap the exposed nucleotides. Ring-shaped clamp proteins form a sliding clamp around the DNA near the point where the two strands are separated to help the polymerase maintain firm contact with the section being replicated.
This is a mere sample of the players involved. As remarkable as it might seem, the entire, fantastically intricate extravaganza is understood in precise detail. And those details, in both number and kind, are almost beyond belief. (This limited description be-lies the true state of affairs.) What is not known, though, is how the whole performance is coordinated so seamlessly, how the strict sequences are timed and reaction rates controlled. And just how seldom things go wrong (especially compared to any human endeavor). A single mistake—just one—can be fatal for any cell. Or, if the error turns up in an egg or sperm cell, fatal to the organism’s offspring. That one slip-up could result in a defective gene, which might lead to the imprecise formation of a single type of protein, which in turn could result in something like type 1 diabetes or sickle cell anemia.
So: accuracy in the entire process is crucial. Suites of repair enzymes proofread the duplicated strands and mend damaged or incorrect sections. Robert Wesson writes:
“One set…monitors that the right amino acid is put in place; another set checks that the newly forming DNA corresponds to its template and cuts out and replaces defective sections; a third confirms the finished product,” in the case of E. coli making less than one error per billion letters. And just for a reminder that these efficient workers are complex machines and not little toy-molecules: one of the repair enzymes, composed of some thousands of atoms, is named phosphatidylinositol 3-kinase-related kinase.
Among its many astonishing properties are DNA’s surprising durability and chemical stability. Still, it is constantly being damaged due to various kinds of physical impairment, from oxidation by free radicals (highly reactive molecules and ions) or, in skin cells, exposure to ultraviolet light or X-rays. But thanks to teams of fix-it enzymes, the DNA of each individual cell can undergo repair from 10,000 to one million times per day, most of it successfully. Close to 170 specific varieties of enzymes are involved with different aspects of DNA repair (including the much different problems associated with sigle-strand repair as opposed to mending a double-strand break). The entire process is now recognized as being absolutely essential for the survival of all organisms. According to recent estimates, without these proofreading and repair systems, roughly 1% of bases would fail to be copied correctly—a quick and certain route to extinction.
Not bad…no, not too bad for something that is “just a chemical.” Bearing in mind that DNA is “only” a molecule, consider once more its bewildering sophistication: a lifeless aggregation of atoms that orders the construction of virtual armies of assistants; these helpers then unwind it, take it apart, and faithfully reattach these fragments after making sure they have been copied accurately. This, a consequence of the DNA having supplied another suite of elaborate protein machines with blueprints for the   assembly of all those helpers (together with furnishing instructions for the fabrication of the machines that built the machines.)
In addition, DNA fixes its own damaged parts and mistakes made while being rep…li…ca…ted. For some reason, incomprehensible to me, most people do not seem to think that self-assisted self-replication is too tall of an order for a mindless molecule.
And as for DNA’s role in the process of genetic inheritance: that equally remarkable saga will be delved into later. Suffice it to say, for now, that the tale shares the same qualities of neat efficiency and dazzling intricacy. Another extensive team of molecular players in backing roles help bring forth all its enormous potential.
Never overlook the fact that DNA is not only entirely passive but utterly useless without the help of its legion of confederates, each of them being equally essential. The miracle molecule is plainly not alive in any accepted usage of the word. But how can we continue to ignore the obvious? That in some sense DNA (along with the entire system-cum-process involving a host of assistants) is animated by the same quality—whatever it might be—that separates living from nonliving? At what point do these far-fetched molecular associations and interactions earn new biological status? Or, from a non-scientific point of view, at least a different sort of emotional response?
Viewing these matters through the lens of Natural Design provides a standpoint from which such wonders meld perfectly with the greater picture of what life is capable of. The double helix could be considered the ultimate expression of nature’s creativity. It did not simply “happen”—it was a necessity invented by nature to fill an indispensable role. The late Bill Gates wrote, “DNA is like a computer program but far, far more advanced than any software ever created.” As a chemical solution to the problems of reproduction and inheritence, it has functioned flawlessly for going on four billion years. True to its paradoxical nature, DNA’s unwavering stability makes life possible while an innate fluidity makes it possible for living things to evolve. And life’s built-in knack for changing through time in beneficial ways is central to its success.      

   ©Tim Forsell   draft                       27 Feb 2017                                                       

[1] Wade, N. (1995) “Method & Madness; Double Helixes, Chickens and Eggs,” New York Times Magazine.  “An ark’s worth of species flower and fade at each tick of the geological clock. Only DNA endures. This thoroughly depressing view values only survival, which the DNA is not in a position to appreciate anyway, being just a chemical.” (Wade, it should be noted, is explicitly writing with reference to Richard Dawkins’ “selfish gene” theory.)
[2] One instance is vertebrate organisms’ red blood cells, which have relinquished their DNA (and the cell’s entire nucleus) in the interest of smallness—the better to navigate through minute capillaries and carry more oxygen.
[3] Unlike covalent bonds, wherein atoms “share” electrons, hydrogen bonds are much weaker. They form between separate molecules when a weakly positive hydrogen in one molecule is attracted to a slightly negative atom in the other. Hydrogen bonds are of great importance in nature (accounting for the fluid properties of water, for instance). The hydrogen bonds between the nucleotides, it should be noted, are a most opportune balance between the strength needed to maintain the molecule’s durability and what is necessary for the two strands to be easily separated.
[4] To be clear: these “letters” form the basis of a language analogy and are unrelated to the bases’ single-letter abbreviations.
[5] Proteins are a class of organic (carbon bearing) molecules. There are around a million known varieties. Unlike inorganic polymers—chains of repeated elements or monomers—proteins are made up of highly specified sequences of modular building blocks called amino acids. Chains of amino acids are joined together to form polypeptides, which are then further processed to create the proteins. These act singly or in combination, making up the cell’s working parts.
[6] Note throughout this work that most of these impressive “facts” are, in actuality, akin to estimates or “educated guesses.” As is customary, they were conveyed without any qualification as to their range of accuracy. Some could easily be off by orders of magnitude.
[7] Estimates of extremely large numbers (some of them apparently little more than wild guesses) may be off by several orders of magnitude. Whatever the figure: it is obviously somewhat arbitrary, particularly when dependent on a number of factors.