The Origin of Life:

Abiogenesis by Chemical Evolution?  

 
How did life begin?  What was the origin of the first carbon-based life on earth?
Scientists are proposing various theories for a natural origin of life by a process of abiogenesis (a non-biological production of life) that can be viewed as a chemical evolution from non-life to life.    {note:  Another meaning of chemical evolution is the natural process, occurring in stars, that forms the nuclei of larger atoms (Li, C, N, O,...) from the smaller nuclei of H and He. }

Scientists usually propose a four-stage process of formation for the first life:
1A. formation of small organic molecules (amino acids, nucleic acid bases,…),
1B. and these combine to make larger biomolecules (proteins, RNA, lipids,…),
2A. which self-organized, by a variety of interactions, into a semi-alive system
2B. that gradually transformed into a more sophisticated form, a living organism.

• Loren Haarsma & Terry Gray (2003) briefly outline a possible process for a natural origin of life. 

Before looking at web-pages with proposals (and criticisms, as in claims for INTELLIGENT DESIGN) for various scientific theories about a natural origin of life, let's get a "big picture overview" of some problems and possible solutions:

        An Outline of Problems
        There are chemistry problems in Stages 1A and 1B, due to some energetically unfavorable reactions and unproductive competitive reactions.
        But the toughest problems are biological, in Stages 2A and 2B, because the simplest possible "living system" seems to require hundreds of components interacting in an organized way to achieve self-replication and energy production, and this organized complexity would have to occur before natural selection (which depends on self-replication) was available.  For these stages we can ask, "Are scientists learning that what is required for life is greater than what is possible by natural process?" or is our current knowledge insufficient to answer this question because we don't yet know enough about what is required and what is possible?

        Problems and Possible Solutions
        For awhile following the Miller-Urey experiments in 1953, a popular theory proposed that life began in a prebiotic ocean filled with a "chemical soup" of organic biomolecules.  But problems with this scenario led to proposals for different types of localized environments, such as an isolated semi-evaporated pond, or a seafloor hydrothermal vent, or in a location that allowed interactions between biomolecules and minerals/clays with organizational or catalytic functions.  Or maybe the original abiogenesis occurred in a very different environment, on another planet or in space.  And although most science has focused on the familiar life that we observe on earth (based on carbon, in aqueous solution), maybe the first life had a different chemical or physical basis.
        All proposals for a transition from nonlife to life must cope with various "chicken and egg" problems.  For example, all modern life involves proteins and DNA, but the production of protein requires DNA, and the production of DNA requires protein, and both require RNA and more, operating in a complex coordinated system.  Could a simple organism be "alive" with only proteins, or only DNA?  But if it had both, it would not be simple, and could this complexity arise by chance?
        To avoid the need for a complex system with proteins plus DNA, some scientists have proposed that RNA (which combines the replicating ability of DNA and catalytic activity of proteins) was the key life-producing molecule in the earliest living cells.  A prebiotic RNA World is still a popular theory, but questions have arisen due to the difficulty of RNA synthesis in prebiotic conditions, and because RNA functionality (in catalytic activity and self-replicating ability) has not matched the initial optimistic hopes.  In response, recent theories have proposed a simpler pre-RNA World with key functional roles played by other molecules.
        Scientists are trying to develop principles for a pre-biological selection that was functionally analogous to (although less efficient than) biological natural selection.  And there is a continuing search for ways to reduce the minimal complexity that would be required for a system with self-replication (with "genes first") or metabolism (if "metabolism first") or both.  {replication or metabolism, which came first?}   But instead of imagining a simplification, some scientists are looking toward complexity for answers to abiogenesis, by proposing that within a complex mixture of chemicals there can be a spontaneous emergence of an autocatalytic network of reactions that is a self-replicating system, and the beginning of life.
 

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Current Theories of Abiogenesis

• Word-IQ has an excellent introductory overview, Origin of Life.
• Loren Haarsma & Deborah Haarsma briefly outline theories about The First Living Cell and explain why "as long as science does not have a definite conclusion, it would be best to exercise some humility and caution" in claiming that, based on what we know from current science, natural abiogenesis is or isn't possible.  And they describe two rational Christian preferences about future scientific research, hoping that science either will or won't be more successful in finding a way for life to begin naturally.

According to Biology-Online, biogenesis is "the principle stating that life arises from pre-existing life, not from nonliving material."  Until the mid-1860s, this principle was opposed by a theory of spontaneous generation claiming that "complex, living organisms may be produced from nonliving matter.  It was a popular belief that mice occur spontaneously from stored grain, or maggots spontaneously appear in meat."  Modern theories of abiogenesis (to form the first life) do not oppose biogenesis (which applies to current life) and do not propose spontaneous generation.
• History of Theories:  Early theories and experiments, into the 1780s, are described by Jack Haas in a historical approach that shows "how vastly different [compared with modern ideas] was the meaning of ‘experiment’ and of ‘scientific work’ in these different times and places."  For the rest of the story, you can get a quick overview from Tami Port and more details from John Wilkins; they explain how clever experiments, leading up to the conclusive demonstrations by Louis Pasteur in the 1860s, showed that spontaneous generation does not occur now.  This history is valuable for clarifying what modern theories are NOT, so we can avoid strawman misconceptions about current theories of abiogenesis, which (as explained in the ISCID Encyclopedia) are much more sophisticated than the simple theories of spontaneous generation from the past.

• A good overview of current theories, written for Talk Origins, is The Origin of Life by Albrecht Moritz,
• Richard Robinson summarizes the history and current state of research ,
• and Wikipedia has a survey-overview of many theories.
• In another part of ASA's website, Jack Haas provides an overview plus news stories regarding current scientific research (and scientific questions) about the origin of life, and he proposes that "one plausible reason for the slow rate of progress is that it is difficult to obtain funding for research in this area, since practical commercial applications for the research are difficult to foresee."

 
Criticisms of Abiogenesis Theories

• Casey Luskin summarizes arguments against a "chemical evolution" origin of life, briefly and in more detail.
• While you're reading the advocates of one abiogenesis theory, notice what they say (it's often criticism) about other abiogenesis theories.  For example, Robert Shapiro criticizes RNA World and defends Reaction Cycles.
• Steve Meyer looks at science and philosophy in a summary paper and longer paper and comprehensive book chapter. (1997, 1996, 2003)
• Richard Deem examines many problems and you can see more by using his bottom-of-page links.
• Craig Rusbult has four pages (scientific, thermodynamic, methodological, philosophical) about The Origin of Life explaining why he thinks "scientists are learning that what is required for life is much greater than what is possible by natural process."
• Fazale Rana & Hugh Ross report on the 1999 conference of ISSOL, the International Society for the Study of the Origin of Life:  story/overview with science summaries and outlines of science-topics.  {analysis of RNA synthesis}
• A classic book from 1984, the first high-quality comprehensive critique of abiogenesis, was The Mystery of Life's Origins: Reassessing Current Theories by Charles Thaxton, Walter Bradley, and Roger Olsen.  You can read three chapters (7 8 9) and a video-interview with Thaxton and textbook critique by Bradley and reviews of Bradley-talk & chapter (on PandasThumb & Infidels) and book reviews (by Steve Meyer & Amazon).
 

Defenses of Abiogenesis Theories

• In an interview with Stanley Miller in 1996 we see an optimistic description of abiogenesis science and its prospects for development, and Miller concludes with a different perspective (compared with Rana & Ross) on the relatively small community of research scientists who are focusing on the origin of life.
• Ian Musgrave criticizes math-based claims for The Improbability of Abiogenesis because, among other reasons, precise specificity is not essential for functionality, and a huge number of "chemistry experiments in nature" can occur simultaneously.
• Talk Origins (Mark Isaak, editor) also has responses to 17 criticisms of abiogenesis, and a links-page for their Abiogenesis FAQs.
• Also, possible solutions for problems are proposed in the overviews above and the sections below.

Criticisms and Defenses continue in the sections below.
 

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The next three sections focus on specific stages of abiogenesis.

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        Stage 1A — PreBiotic Chemistry (Miller-Urey and more)
        Modern studies of prebiotic (pre-biological) biochemistry — to form organic molecules and biomolecules in Stages 1A and 1B — began in 1953 with the Miller-Urey Experiment.  Early MU experiments used a reducing atmosphere with reactive chemicals (CH4, H2, and NH3) plus H2O.  Within two decades, most geologists thought the early earth had a non-reducing neutral atmosphere (mainly CO2 and N2 plus H2O) that was much less reactive;  when these chemicals were used in later variations of MU the yields of organic molecules were much lower.  But geological questions about earth's early atmosphere continued through the 1990s, and in 2005 calculations about gas from chordites indicated that the atmosphere might have been reducing, similar to the early MUs.  Currently the chemistry of the early atmosphere is in doubt, as described in Wikipedia.
        There have been questions about other aspects of Miller-Urey experiments, such as the choice of energy sources and why newly formed products were isolated (before they could be broken down by further reactions), to ask whether the MUs were realistic simulations of conditions on the early earth.
        In response to these questions and their own, researchers studied a wide variety of Miller-Urey variations, using different reactant mixtures, energy sources, and conditions, and in the reaction products they observed a variety of organic compounds, in amounts that spanned a wide range but usually were fairly low.
        In addition, scientists discovered that objects from outer space (meteors, comets,…) contain interesting organic compounds, plus H2O, and these compounds would have become "part of the reaction mixture" when the space-objects landed on earth.

• On the 50th anniversary of the Miller-Urey publication, a report from Astrobiology Magazine.
• For an overview of current views on the early atmosphere, read the section on "Conditions for Synthesis of Organic Molecules on the Early Earth" in the page by Moritz.
• Talk Origins has brief responses about the early atmosphere: A & B.
• Jeffrey Bada ran a recent variation of Miller-Urey that produces more amino acids, but not nucleic acid bases.

 
      Stage 1B — Polymer Chemistry (to make proteins, RNA,…)
      The Miller-Urey experiments are about stage 1A, forming small organic molecules.
In 1B, problems occur due to energetics — because in water the reactions to form larger biomolecules (proteins, RNA, and DNA) are energetically unfavorable — and also due to competition.
      For example, during protein synthesis a prebiotic reaction mixture would contain many different chemicals (L-amino acids and R-amino acids, plus many other molecules) and the majority of newly formed bonds would not be the special peptide bonds (linking only L-amino acids) found in natural proteins.  The scarcity of L-peptide bonds is partly due to the fact that in a watery "soup" the formation of these bonds is energetically unfavorable.  Therefore, abiogenesis researchers have searched for and studied non-aqueous reaction sites, such as evaporated ponds or on the surface of minerals.
      Similar difficulties would arise in the prebiotic formation of other important biomolecules.  Problems occur in both stages of forming RNA, in forming ribose sugars and some nuclotide bases (in 1A) and connecting these together (in 1B).  The prebiotic synthesis of RNA has been especially unsuccessful, but perhaps special environments (such as the surface of minerals) could help with the reactions.

• In the "General Considerations" section of From Building Blocks to the Polymers of Life says, "the formation of either proteins or RNA from their monomers is not energetically favored… [so]… in the presence of water… energy input was necessary to have made RNA and polypeptides on primitive Earth."   { Later, there is more about synthesis problems in an RNA World. }
• For possible solutions to another problem, click the link for "Origin of the Homochirality of Amino Acids & Sugars" in Moritz and read about a crystal with 10% separation of L & D amino acids.

 
      Stages 2A & 2B — Chemical Evolution into the First Life
      Most scientists think the most challenging problems for abiogenesis by chemical evolution are biological, in Stages 2A and 2B, because "The simplest possible ‘living system’ seems to require hundreds of components interacting in an organized way to achieve self-replication and energy production, and this organized complexity would have to occur before natural selection (which depends on self-replication) was available."
      What is life?  Michael Pidwirny summarizes the answer given by Daniel Koshland in The Seven Pillars of Life.  But which of these would have been necessary (or useful) during each part of a natural chemical evolution through stages 2A (semi-alive?) and 2B into being fully alive?  Asking "why is it difficult to define life?" draws responses, brief (Joel Achenbach) and in detail (Carol Cleland & Christopher Chyba).
      What is the minimal complexity required for life? At the end of his Introduction, Moritz summarizes current ideas: "The most elementary [non-parasitic] cells we currently know… have 482 protein-coding genes (most bacteria, such as E. coli, encode for more than 2000 different proteins)" plus some non-protein molecules; of these, "according to the probably best experimental study to date (abstract & full text) the essential ones are 387" and "the likely most accurate hypothetical study (abstract & full text) puts the minimal number of genes at 206.  All the proteins produced from these genes are involved in a maze of pathways of metabolism, replication, as well as building and maintenance of structure, which is of bewildering complexity."

      Gene-First or Metabolism-First?
      Scientists currently have two main theories about the first functionality in the development toward life:  Was it genes-first or metabolism-first or some of each?   {some possibilities}   But with either type of scenario, at some point in its journey toward becoming a living cell it would need to construct a membrane to separate itself from the external environment.  But, as Richard Deem, explains, there are problems with a prebiotic synthesis of cell membranes.
• Leslie Orgel discusses gene-first & metabolism-first theories for a "chemical evolution" origin of life.

      Genes-First in an RNA World
      To avoid the need for a complex system of proteins plus DNA (with hundreds of proteins required for life) some scientists have proposed that RNA — which combines the replicating ability of DNA and catalytic activity of proteins — was the key life-producing molecule in the earliest living cells.
      This common proposal is described in many pages in other sections, and is the main focus of these pages:
• Leslie Orgel (1997) proposes a prebiotic RNA World in The Origin of Life on Earth.
• What can RNA do?  Jack Szostak is exploring the possibilities, in an attempt to produce RNA-life in the lab.
• Richard Deem looks at problems (synthesis,…) of an RNA World and so do others, including Robert Shapiro ( 1  2 ) and Gordon Mills & Dean Kenyon.
• Recently, scientists determined the 3-D structure of a ribozyme (an RNA enzyme).

      Metabolism-First with Chemical Reactions
      Some scientists think life was an emergent property that happened, either gradually or suddenly, due to interactions between chemicals in a complex system.  A "metabolism first" view is an approach, not a specific theory, and various advocates propose different chemical mixtures and reaction locales:
• An origin of life beginning with small-molecule interactions is described by Robert Shapiro, briefly and (after criticizing RNA World) in more detail.
• Loren Haarsma & Terry Gray briefly outline the basic ideas of abiogenesis in an autocatalytic system.
• Leslie Orgel, an advocate of genes-first, criticizes metabolism-first.  (pro-ID commentary by Casey Luskin)
• Moritz writes a lot about metabolism-first, from "Specificity of Chemical Reactions" onward.
• One possibility, among many, is a hypercycle.
• Bruce Weber has an outline of ideas about life arising from interactions in complex systems.
• Christian De Duve, in 1995, compares an RNA World and Thioester World.
• Michael Russell & Allan Hall look at possibilities in warm underwater springs and converting CO2 into acetate and then life.
• James Ferry & Christopher House study microbes that metabolize carbon monoxide and they propose a way to reconcile heterotrophic and autotrophic theories for the origin of life.
• a book review of Genesis: The Scientific Quest for Life's Origins (by Robert Hazen) about emergent cycles and ocean vents, minerals and more.
• In the late-1980s, Graham Cairns-Smith proposed that life began as "clay organisms" that transformed into DNA-based life, but this idea is not currently popular or influential.  A website about the role of Clays & Crystals in the Origin of Life includes articles, links, and criticisms;  another critique is from Charles Thaxton & Stephen Meyer.
 

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      Panspermia — Extraterrestrial Origin of Life?
      Some scientists think our two initial questions (re: the first life, and first life on earth) have different answers, because the first life did not begin on earth.  Usually, scientists proposing theories of panspermia (or directed panspermia) wonder if conditions elsewhere in the universe might have been more conducive to the formation of life.
• ISCID Encyclopedia, basic principles
• John Gribbin, introductory summary
• Jay Withgott, Panspermia: Seeds from Space
• Casey Luskin, Problems with Panspermia
• David Warmflash & Benjamin Weiss, Did Life Come from Another World?
• Among the few scientists proposing directed panspermia are Francis Crick and Leslie Orgel.
• Brig Klyce has a comprehensive website about Cosmic Ancestry: The Modern Version of Panspermia.

      Panspermia would require an extraterrestrial origin of life, on another planet or even in space.  But a natural abiogenesis to form life could have occurred only elsewhere (then brought to earth by panspermia) or only on earth, or both, or neither.
• If astrobiology is to have an empirical basis, scientists and engineers must ask, How do we Search for Life in Alien Worlds? and maybe they should consider unusual un-earthlike environments.
• a book-summary of Bruce Jakosky's Search for Life on Other Planets
• You can learn about NASA's multi-faceted exobiology programs in a brief abstract and a multi-part Astrobiology Roadmap that explains ideas and research strategies, and an overview with "Related Links" to explore, including the SETI Institute (Search for Extraterrestrial Intelligence).
• paper-summaries (about astrobiology & astronomy) from Scientific American's Magnificent Cosmos

 
      Multiverse — Can events that seem extremely improbable happen anyway?
      IF a natural origin of life is extremely improbable in our universe, and IF we live in a multiverse containing an immense number of universes similar to our own (with the same properties of nature), THEN even though a natural origin seems improbable, maybe it actually is not improbable.  Why?  Because if enough universes exist, even highly improbable events (like a natural origin of life?) will happen somewhere in one or more of the many universes, and evidently — because we are alive — we live in one of those places!  This is the logical basis of a claim that a multiverse is a way to beat the odds for a "fine tuning" of nature, or for events (like the origin of life) that occur during the history of nature.
• Eugene Koonin claims that although a natural origin of life is highly improbable in our universe, in a multiverse it would be probable and would occur somewhere, and here is where it happened.  You can read Koonin's abstract and paper, plus comments (by referees & author) in HTML or PDF.
• OUR UNIVERSE — INTELLIGENT DESIGN and/or MULTIVERSE is a links-page examining claims for a design of nature, and for design-directed action during history as an explanation for features such as the first carbon-based life.
 

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        An Overview/Analysis of Views
        Let's look at different views of origins, in terms of possibilities for the origin of the first carbon-based life on earth.  Maybe this origin was natural and a plausible Non-Design theory is possible, in principle, and the correct theory:  N1) is currently known (whether or not it currently seems plausible), or  N2) will be known in the future, or  N3) will never be known because the natural process was too complex or unfamiliar or cognitively difficult for us to propose.  But perhaps it's impossible to construct a Non-Design theory that is plausible (that would have a reasonable probability of happening) because:  N4) the natural origin was highly improbable even though it did occur, or  N4*) the N4-origin seems improbable but actually is highly probable because we live in a universe that is one of an immense number of universes in a multiverse that was either designed or undesigned *.  Or the first earth-life might have been produced by Design-directed action, with  D1) natural design and construction, or  D2) supernatural design and creation.  Or maybe it happened some other way, X.   {* All possibilities — N1 to N4 plus D1, D2, and X — could occur in a universe (which probably would have to be designed) or a multiverse (either designed or undesigned). }
        In currently conventional science, scientists define their goal as N1 or N2;  those with confidence claim N1 with current plausibility, those with less confidence claim N1 with current implausibility, or N2, N3, N4, or X;  an appeal to "inevitability in a multiverse" (with low confidence in abiogenesis theories, but high confidence in multiverse theories) is N4*;  undirected panspermia is N1 (for the "panspermia" claim) preceded in history by any of the possibilities for the earlier origin, while directed panspermia is D1 preceded by any possibility;  the scientific proposals of Intelligent Design are for "either D1 or D2";  some creationists (either old-earth or young-earth) propose direct divine creation by D2, while evolutionary creationists propose indirect divine creation that is compatible with any possibility (if it followed the divine designing and creating of a universe or multiverse that would naturally produce life) not involving D2;  and an atheist, or a rigid agnostic, can accept any possibility except direct divine creation (D2) or indirect divine creation.
 

 

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