All livings things on Earth, both in the present and in the past, share a single, common ancestor that lived roughly 4 billion years ago.
Peter Russell, iGenetics
How biological life originated on Earth remains a profound mystery. Denton provides a basic introduction to the question when he writes:
…the first cell is supposed to have arisen following a long period of pre-cellular evolution. The process is presumed to have begun with a primitive self-replicating molecule which slowly accumulated beneficial mutations that enabled it to reproduce more efficiently. After eons of time, it gradually evolved into a more complex self-replicating object acquiring a cell membrane, metabolic functions and eventually all the complex bio-chemical machinery of the cell.
Michael Denton, Evolution: a Theory in Crisis
He then goes on to describe some of the issues that scientists face in providing a complete and credible explanation:
The existence of a prebiotic soup is crucial to the whole scheme [models for the origin of life]. Without an abiotic accumulation of the building blocks of the cell no life could ever evolve. If the traditional story is true, therefore, there must have existed for many millions of years a rich mixture of organic compounds in the ancient oceans and some of this material would very likely have been trapped in the sedimentary rocks lain down in the seas of those remote times.
Yet rocks of great antiquity have been examined over the past two decades and in none of them has any trace of abiotically produced organic compounds been found…Sediments from many other parts of the world dated variously between 3,900 million years old and 3,500 million years old show no sign of any abiotically formed organic compounds.
…In the presence of oxygen any organic compounds formed on the early Earth would be rapidly oxidized and degraded. For this reason many authorities have advocated an oxygen-free atmosphere for hundreds of millions of years following the formation of the Earth’s crust.
…Without oxygen there would be no ozone layer in the upper atmosphere which today protects the Earth’s surface from a lethal dose of ultraviolet radiation. In an oxygen-free scenario, the ultraviolet flux reaching the Earth’s surface might be more than sufficient to break down organic compounds as quickly as they were produced.
… “Catch-22…If we have oxygen we have no organic compounds, but if we don’t have oxygen we have none either.
Recently, an Australian group reported the remains of a simple type of algae in rocks at least 3,500 million years old, and other rocks almost as ancient in other parts of the world have also yielded evidence of life over the past few years.
…The most difficult aspect of the origin of life problem lies not in the origin of the soup but in the stages leading from the soup to the cell.
…The complexity of the simplest known type of cell is so great that it is impossible to accept that such an object could have been thrown together suddenly by some kind of freakish, vastly improbable, event. Such an occurrence would be indistinguishable from a miracle.
Michael Denton, Evolution: a Theory in Crisis
One of the possibilities that would bypass many of the obstacles Denton’s lists above is the possibility that the first life originated in deep oceans away from killing ultraviolent radiation and atmospheric oxygen, like the extremophiles today that thrive near hydrothermal vents deep in the ocean.
Even so, significant hurtles remain:
The problem of the origin of life is not unique—it only represents the most dramatic example of the universal principle that complex systems cannot be approached gradually through functional intermediates because of the necessity of perfect coadaptation of their components as a pre-condition of function.
…The only alternative is to consider the possibility of saltation. However, the probability of a sudden fortuitous event assembling the first cell de novo has generally struck most biologists as outrageously improbable. Yet, if gradualism is impossible, there may be no alternative but to presume that such an extraordinarily lucky accident was responsible for creating the first cell.
Michael Denton, Evolution: a Theory in Crisis
Another problem that faces scientists attempting to explain how life began is that...
...the simplest cells available to us for study have nothing “primitive” about them…no vestiges of truly primitive structures are discernible.
Michael Denton, Evolution: a Theory in Crisis
This means that we have no existing biological roadmap as to how the first cell might have developed. The world is filled with single-celled bacteria and many more complex forms up to and including humans, providing such a biological roadmap that at least includes major steps along the evolutionary way. But between naked chemistry and the simplest of cells (ones still remarkably complex), we have virtually nothing to go by, nothing that exists in nature (and rarely in a lab) that might provide crucial links that once evolved into the first living cell. “The only way to make a new cell is through division of a pre-existing cell.”
Richard Dawkins asks us to embrace the possibility of a tremendously unlikely combination of events in the distant past:
Suppose we want to suggest, for instance, that life began when both DNA and its protein-based replication machinery spontaneously chanced to come into existence. We can allow ourselves the luxury of such an extravagant theory, provided that the odds against this coincidence occurring on a planet do not exceed 100 billion billion to one.
But although we are entitled, in our theory of the origin of life, to spend a maximum ration of luck amounting, perhaps, to odds of 100 billion billion to one against, my hunch is that we aren’t going to need more than a small fraction of that ration. The origin of life on a planet can be a very improbable even indeed by our everyday standards, or indeed by the standards of the chemistry laboratory, and still be sufficiently probable to have occurred, not just once but many times, all over the universe.
Richard Dawkins, The Blind Watchmaker
In our exploration of a living cell we will review in detail the intricacies that Dawkins seriously suggests arose spontaneously, and put that notion to rest. Without some other (unknown) aspects of nature, the possibility that such molecular machinery could simply fall into place and function effectively is impossible. A proper explanation for the origin of life will include natural elements and not the probabilistic miracle that Dawkins suggests.
Another possibility exists, one we touched upon earlier. It’s possible biological elements simply exist as part of the fabric of the universe:
Information theorist Huber Yockey argues that the information needed to begin life could not have developed by chance; he suggests that life be considered a given, like matter or energy.
Michael Behe, Darwin’s Black Box
This seems highly unlikely, as the distance in complexity and substance between bacteria and basalt (that is, between the living and the non-living) represents the most profound gap in nature. That and the fact that we have yet to discern any evidence for life existing anywhere but Earth suggests that the existence of life does indeed merit special explanation.
A recent publication reviews the status of current Origin of Life (OoL) studies and what it will take to make significant progress in determining how life originated. The scientific community is challenged across several distinct disciplines to coordinate their research in order to succeed. The following model from the same article does a nice job expressing the state of OoL studies, the need for inter-disciplinary participation, and the principle questions that require attention:
The model clearly indicates that we don’t know how life originated.
Many theories have been expressed, as noted in the article:
The list of individual theories, different lines of experimental and theoretical research and diverse views on the OoL is extensive and eclectic.
Various Authors, The Future of Origin of Life Research, 2/26/20
While differences abound, general agreement does exist in a few areas:
There is some consensus on a few points. First, the earliest undisputed fossil evidence places life on Earth prior to 3.35 Ga [Giga annum, or billion years] and molecular clocks suggest an origin prior to the late heavy bombardment >3.9 Ga. Second, the origin of life must have resulted from a long process or a series of processes, not a sudden event, for the complexity of a cell could not have appeared instantaneously. The OoL must have started from simple abiotic processes, involving one or more sources of energy and matter…forming protometabolism, compartmentalization and inheritance. But strikingly, the list of agreements does not expand much further than this.
Various Authors, The Future of Origin of Life Research, 2/26/20
The bottom-up approach to OoL research begins in the lab in an effort to simulate primitive conditions and produce organic molecules and replicate processes we see in living cells. While these efforts have enjoyed some success, serious questions remain:
Given that virtually all of the origins hypotheses are non-falsifiable, the diversity of the bottom-up approaches mentioned here has led to an important question: to what extent do the experimental synthetic advances resemble what actually happened at the OoL? With the complete set of inorganics and ready-synthesized organics at its disposal (plus a wide range of experimental conditions), the bottom-up approach parallels an artistic endeavor that can paint both abstract and realistic pictures of the first biomolecules and their assemblies. For this reason, to constrain the experimental space, clearer pictures of i) the fundamental features of life, ii) ancestral life forms and iii) the environmental conditions at their origin are urgently required.
Various Authors, The Future of Origin of Life Research, 2/26/20
As a non-scientist, one of the impressions I get after learning about these bottom-up efforts is increased amazement at the depth of the OoL mystery. Despite the unlimited options available within a modern scientific lab, with every condition, element, and energy source at their disposal, scientists have continued to fail in reproducing a single major element of cellular life. A few amino acids here and there, some suggestive results with lipids, for example, yet nothing that approaches the organization, complexity or integration of a living thing.
A top-down approach looks at living organisms and attempts to trace their origin through emerging genetic studies, and the first results were encouraging:
Modelling early evolution and the OoL required a precise and holistic way to trace species back in time, and that came first in the form of genome sequences. Prokaryotes, the simplest forms of cellular life, are increasingly supported by evolutionary studies as the oldest lifeforms, and thus of utmost importance for OoL research. The first comparison of prokaryotic genomes revealed a conserved set of 240 genes.
Various Authors, The Future of Origin of Life Research, 2/26/20
Isolating these conserved genes provided evidence pointing to a specific set of genes that may have been there at the beginning. But further research revealed a more complicated truth:
Later, the exponential growth of the number of sequenced genomes came with a daunting realization: the prokaryote world is highly diverse, full of redundancy with non-orthologous gene displacements…and lateral gene transfer, and the intersection of genomes shrank to a mere handful of ribosomal genes. The search for the genetic content of LUCA—the Last Universal Common Ancestor—using the classical comparative top-down approach had thus stagnated.
Various Authors, The Future of Origin of Life Research, 2/26/20
Beyond these approaches...
... many pre-biotic worlds came to light with their own preferred class of biomolecules and significant insights, e.g., protein…, lipid, coenzyme, and even virus worlds are some of the most popular theories for the order and/or relevance of appearance of biomolecules on Earth.
Various Authors, The Future of Origin of Life Research, 2/26/20
We still don’t know the nature of any pre-biotic world:
The relative abundance and distribution of building blocks of the main classes of biomolecules ~4 Ga ago on Earth is still elusive and a matter of strong debate.
Various Authors, The Future of Origin of Life Research, 2/26/20
As mentioned earlier, the lack of evidence for pre-biotic ‘soup’ containing organic compounds makes all these pre-biotic worlds problematic:
Classical approaches in OoL have often been constrained to biomolecules due to their ubiquity in biology, however, most of these biomolecules were not necessarily available at early prebiotic stages. Prebiotic environments most likely included compounds not central to modern biopolymers…
Various Authors, The Future of Origin of Life Research, 2/26/20
Two classical theories include the popular ‘RNA World’ and the ‘metabolism-first’ theory. The former posits...
...A world with a jack-of-all-trades RNA molecule, catalyzing the formation of indispensable cellular scaffolds, from which somehow then cells emerged. [my emphasis]
Various Authors, The Future of Origin of Life Research, 2/26/20
Problems with this theory include the lack of templates for assembling RNA molecules within the prebiotic mix, and the inherent instability of the RNA molecule under various conditions of heat and radiation.
The ‘metabolism-first’ theory favors...
...simpler molecular networks harnessing energy from geological disequilibrium leading to the emergence of genetic complexity.
Various Authors, The Future of Origin of Life Research, 2/26/20
Regardless, the question of which biomolecules initiated the origin of life remains problematic, as...
...All known living cells contain DNA, RNA, proteins, lipids, coenzymes, and other metabolites—and the earliest cells as those known on Earth would have had to fulfill these minimal cell requirements.
Various Authors, The Future of Origin of Life Research, 2/26/20
There is a compelling argument that these original essential biomolecules emerged simultaneously and were interrelated. Recent advances support this possibility:
The findings add credence to the idea that both DNA and RNA developed together from the same sort of chemical reactions at the beginning of life on our planet, and that the first self-replicating molecules could have been mixes of both these nucleic acids – not just RNA, as suggested in the more established 'RNA world' hypothesis.
David Nield, There's Mounting Evidence That Life on Earth Started With More Than Just RNA 1/1/2021
What must be kept in mind, though, is that these biomolecules do not represent the origin of life or the cell, as...
...Cells are not mere collections of their chemical components, but highly dynamic, complex systems with multiple interlocked processes involving those components. For this reason, the emergence of life cannot be distilled down to biomolecular retrosynthesis only.
Various Authors, The Future of Origin of Life Research, 2/26/20
In other words, even if we possessed a credible model for the emergence of biomolecules, the explanation for the origin of life would remain elusive.
Metabolism is essential for life, but there are other requirements:
Along with metabolism, life is based on another equally-important fundamental principle: inheritance, also described as “information that copies itself.”
Various Authors, The Future of Origin of Life Research, 2/26/20
It’s difficult to understand how one (metabolism or inheritance) could have emerged without the other. This raised the fundamental question as to how they are linked:
Nature’s elegant solution is the genetic code, the origin of which remains a true enigma.
Various Authors, The Future of Origin of Life Research, 2/26/20
The nature of that enigma is revealed when we consider that...
...the code today is self-referential, that is, the mapping between amino acids and codons heavily relies on encoded proteins. When, why and how did non-coded peptides become involved?
Various Authors, The Future of Origin of Life Research, 2/26/20
We will explore this question in detail later, where the translation from the DNA code as transcribed by mRNA into sequential amino acids to create proteins is reviewed in some detail, the origins of which remain unexplained.
The authors finish by saying that...
Answers on the origin of the code still seem very distant.
Various Authors, The Future of Origin of Life Research, 2/26/20
Needless to say, the origin of life remains a scientific mystery, with seemingly impossible obstacles to overcome, both in terms of explanation as well as how life actually emerged in the first place. The key to this mystery most certainly resides within the Vicarian Domain, in one form or another.
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