Origin-of-Life Interview with Edward Peltzer
A student of Stanley Miller and Jeffrey Bada explains the failure of materialistic origin-of-life scenarios
I got to know Ed Peltzer almost two decades ago when Jonathan Wells and I were writing the origin-of-life chapter for The Design of Life, a chapter that got spun off into its own book titled How to Be an Intellectually Fulfilled Atheist (Or Not). Ed supplied me with a wealth of insights, underscoring the many problems faced by naturalistic origin-of-life scenarios. On his recent retirement, I thought I would revisit the topic of the origin of life with him. He graciously agreed to the following interview, which is as good an overview of origin-of-life research as you will find. Enjoy …
Biosketch: A seasoned ocean chemist, Dr. Edward T. Peltzer has long been profoundly interested in the origin of life. During his doctoral studies at the Scripps Institution of Oceanography (SIO), he was mentored by two luminaries in prebiotic chemistry: Stanley Miller, renowned for the Miller-Urey experiment simulating early Earth conditions, and Jeffrey Bada, an expert in the field of amino acid racemization and a prominent figure in the study of organic compounds in meteorites. This mentorship deeply influenced Peltzer’s perspective on abiogenesis. Throughout his career, he has engaged in discussions and presentations on the complexities of life’s emergence, often emphasizing the challenges inherent in explaining the transition from inorganic to organic matter. His collaborations and dialogues with leading scientists in the field underscore his commitment to exploring this fundamental scientific question.
As an ocean chemist, Dr. Peltzer served as a Senior Research Specialist and Chemical Safety Officer at the Monterey Bay Aquarium Research Institute (MBARI) from 1997 until his retirement in August 2024. He earned a B.S. in Chemistry from Bucknell University in 1972 and a Ph.D. in Oceanography from the University of California, San Diego, Scripps Institution of Oceanography (SIO) in 1979. Prior to joining MBARI, he was a research associate at the Woods Hole Oceanographic Institution from 1977 until 1997. At MBARI, Peltzer was part of a team of scientists and engineers that developed innovative in situ technologies, including the Deep Ocean Raman In Situ Spectrometer (DORISS), enabling real-time chemical analysis in extreme marine environments. His research significantly advanced understanding of ocean acidification, gas hydrates, and carbon cycling, contributing to over 100 peer reviewed publications and numerous collaborative projects. He also played a key role in the development of the Free Ocean CO2 Enrichment (FOCE) systems, facilitating controlled studies of ocean acidification impacts in the deep sea.
William Dembski: Thanks so much, Ed, for being willing to take part in this interview about the origin of life, a topic that has exercised you for many years. But before we get to that, let’s get some preliminaries out of the way. Give us some background about yourself. Where and when were you born? What are some things that stand out about your family life? What were some of the early influences on your intellectual formation? Were you raised in a religious home and what impact, if any, did your religious or non-religious background have on you?
Edward Peltzer: Let’s begin at the beginning: I was born in Baltimore, MD in 1950, but grew up in the suburbs outside of the city near Towson. My mother was Roman Catholic and as near as I remember, we went to church every Sunday and every Holy Day of Obligation. My brother and I used to joke that mom was more Catholic than the Pope. Obviously, belief in God was deeply instilled in us and we never questioned that belief.
I attended public school from 1st through 12th grade. Interestingly, back then, biology classes in Maryland were just beginning to teach evolution, so the teachers did not have a strong attachment to the theory. It was mentioned occasionally but I don’t remember any intense focus on it. It certainly was not promoted as the central theme uniting all of biological science with any of the intensity as it is today. Although at the time, I doubt if I would have had any serious conflict with it as within Catholicism “theistic evolution” was quite acceptable. God was in the background pulling the strings and guiding evolution along His chosen path. Likewise, the Biology classes weren’t being used to brow-beat the students into accepting a totally materialistic worldview as many are today.
My doubts about evolution would arise much later in life when I knew enough to seriously look into the proposed mechanisms and processes involved. Back then, those on the pre-college academic track took biology in the 9th grade in junior high school and then chemistry and physics in senior high school. When I took chemistry in 10th grade, I knew I had found my life’s calling. I still remember the day when Mrs. Rosenbaum was explaining the electronic structure of the atom, and I looked up at the Periodic Table on the wall, made the connection and instantly knew why the Elements were arranged the way they were.
WD: Tell us about your primary and secondary education. What were the high points of it? What were the lows? What were some of the questions that most stimulated you during this time?
EP: To be honest, I was a slow starter. Early reading books like “See Spot Run” did nothing to capture my attention. School was boring and unchallenging until I hit the fourth grade. It was Mrs. Gorsuch who realized that my frequent questions weren’t because I wasn’t paying attention, but rather because I wanted to understand more than she had to offer. When we had a unit of the Solar System, I remember asking how come planets were spheres and not flat like spinning pizza dough? The rest of the kids laughed because everybody knew planets were “round like baseballs” as that was what the teacher had just told them.
That’s when she realized that I was asking why and how planets were spheres, not whether they were flat disks or oblate spheroids. Being a smart teacher and knowing that she didn’t have an answer that would satisfy me, she challenged me to answer my own question. And that is when I discovered the encyclopedias in the school library (they were the internet search engines of the 1950s & 60s) and to use the Dewey decimal system in order to find books on Astronomy in the library. That is also when I began to learn to answer my own questions and discovered the joy of learning.
WD: Next, let’s turn to your college and university days. Describe the course of your study and what ideas most excited you during those years. What prompted you to pursue a doctorate in oceanography and what did you hope to accomplish with this degree?
EP: I went to college with a singular focus to learn chemistry. From 10th grade on I knew I had a talent for it, and while taking AP chemistry in 12th grade, it was apparent to all my teachers and classmates that I should major in chemistry in college. During my freshman year at Bucknell, chemistry majors and upper-class pre-med students took organic chemistry. The pre-med program used organic chem to weed out those students who weren’t going to survive in med school. The chemistry department assumed that chemistry majors had already studied general chemistry in high school and that you were in college now: time to step up your game and learn or find another major.
I loved the challenge and met it head on. I did very well in the classroom, so much so that out of over 100 students in that class I was 1 of 2 selected by the professor to do independent research with him that summer. And there was a stipend, so I got paid for it and did not need to hunt for a summer job! That went so well that when Dr. Heine took a year long sabbatical at the University of Heidelberg in West Germany, he invited me and the other student to come to Germany for the month of January to work with him in the lab there. We would continue the research we had started the previous summer. It was an opportunity of a lifetime and confirmed my decision to become a chemist.
During my sophomore and junior years, I followed the standard chemistry major sequence of courses: inorganic chemistry and quantitative analysis, followed by a year of physical chemistry. P-chem proved to be the biggest challenge of my academic career. In fact, it almost did me in. Fortunately, I did well enough in the lab portion of each semester to eke out a C. Realizing that a C in one of my major classes was going to be a problem getting into graduate school, I began to consider other options.
One day, while perusing a graduate school catalog for the University of Miami — figuring that if I was going to be in school for another 3-4 years, I might as well go to someplace where the weather is nice — I discovered a PhD program in Ocean Chemistry. I was dumb struck: I can get a degree in a subject I love (chemistry) and go to sea (which I also loved) at the same time and get a job where they pay me to do it! This was beyond my wildest dreams. And if the admissions committee will overlook my one not so stellar year, maybe there will be life after P-chem.
After consulting with a professor in the geology department about how to pursue a career in oceanography, I radically rearranged my senior year class schedule to satisfy the diverse course requirements for admission to graduate programs in oceanography and proceeded to apply to multiple graduate schools. This change of my career objective did not sit well with my organic chemistry professor who had sponsored my trip to Germany. He envisioned me becoming an organic chemist, not wasting my talents on oceanography. However, that all changed when I applied to Scripps Institution of Oceanography (SIO).
Unbeknownst to me, the chair of the admissions committee at SIO was Dave Keeling, who had also been on sabbatical at the University of Heidelberg the same year Harold Heine was there. As the only two American professors in the chemistry department that year, they became friends. When Keeling saw my application contained a recommendation from Heine, he called him on the phone to find out more about me. I would love to have listened in on that conversation. The end result was two-fold: Keeling convinced Heine that I would not be wasting my talents for chemistry by getting a PhD in oceanography. In fact, the field needed lots of young chemists as it was growing rapidly. Heine convinced Keeling that I was more than up to the challenge and it would be SIO’s loss if they did not accept me into their doctoral program.
Later that day I was summoned to Harold Heine’s office where he told me about the phone call, that Keeling had convinced him of the need for bright young chemists in oceanography, and that SIO was by far the best place to study. He also told me that if offered admission to SIO, I should go there regardless of whether I was accepted anywhere else, and that I had better work my tail-off when I got there as he had given me a strong recommendation, thus his reputation and that of Bucknell was on the line. Suddenly, I was back in Dr Heine’s good graces and the acceptance letter to SIO came a few days later. And that is how I got started on my path to become an oceanographer.
WD: How did your interest in the origin-of-life field first develop? Was there a particular moment or experience that sparked your curiosity?
EP: This was another one of life’s fortuitous events. Having focused on organic chemistry as an undergraduate, I decided that I had to take the class in organic geochemistry during the spring semester of my first year in graduate school. That was taught by Jeff Bada. That first class with Bada was all about the origin of the elements and the formation of the solar system. Our second class together looked at the origin of organic compounds on Earth, which then led to the various theories for the origin of life. The Miller-Urey experiment was featured prominently. Towards the end of the class, Bada talked about the recent discovery of amino acids in the Murchison meteorite and that they had a similar distribution to what Miller found in his experiment.
Consequently, Bada predicted that it was likely that, in both the Miller experiment and the Murchison meteorite, the amino acids were formed via the Strecker-cyanohydrin pathway. If that were true, then we should also find a similar distribution of hydroxy acids in the meteorite formed by a branch in the Strecker-cyanohydrin synthesis pathway. Bada then “baited his hook”: he confessed that he had a contact with access to a pristine portion of the Murchison meteorite, and that discovery of hydroxy acids in that meteorite would make for a great thesis project and it would bring the Miller-Urey experiment back into the forefront of origin of life studies.
That night I thought about this offer and realized that I was hooked by the challenge. The next day I went to see Dr. Bada and said that if no one else had spoken up, I would like to take up the challenge as my thesis project. Jeff did not immediately accept my offer. Instead, he asked me how I might isolate and detect the hydroxy acids in the meteorite. Having thought about this the night before, I immediately responded with a plan. I would use the same extraction technique used by the folks at NASA that found the amino acids, use a two-step ion-exchange process to isolate the hydroxy acids, convert those acids to their methyl esters with diazomethane and analyze them with gas chromatography. Again, Jeff did not immediately respond. I think I surprised him that I had not only thought about taking up the challenge, but that I had a plan for how to do so. He also may have been thinking about where he was going to get the money to buy a gas chromatograph for his lab as I would obviously need one. Before I left his office that day, he did agree to take me on as one of his students.
Long story short, my analytical plan (with a minor enhancement) worked as intended, and after proving it worked by analyzing a sample from one of Miller’s many electric discharge experiments and finding the suite of hydroxy acids just as predicted, I was allowed to proceed with analysis of the meteorite. Bada made good on his promise to obtain a sample of the meteorite for me. The results were published in Nature in 1978: α-Hydroxycarboxylic acids in the Murchison meteorite. DOI: 10.1038/272443a0. Not a bad way to start one’s career with a publication in one of science’s premier journals.
WD: (Indeed, the very journal where Watson and Crick had published the structure of DNA back in 1953—arguably Nature was not just one of science’s premier journals but the premier science journal!) During your time at Scripps, you worked under Stanley Miller and Jeffrey Bada—two giants in the field. What was it like learning from them, and how did they influence your thinking about prebiotic chemistry?
EP: I did have many discussions with Miller and Bada on many subjects, but the issues of pre-biotic chemistry and the origin of life were the most common. Both were excellent chemists. You could ask them about almost anything and they would have an answer or know where one could look to find out. In some cases, I suspected they already knew, but wanted to give me the experience of scouring the library to find out. One could say that they taught me everything I knew about prebiotic chemistry at the time. In the 48 years since then, I have kept an interest in following some of the developments in the field. I find it remarkable at how resilient their ideas and theories are in having stood the test of time. Looking back, I had a remarkable opportunity to, as you say, learn from two giants in the field. At the time, I was just working on my thesis.
When I had completed my research and was writing my thesis and wondering where I would go next, they both gave me some very good advice. While they recognized my analytical talents, they also knew my access to samples would be limited. All the carbonaceous chondrites in museums around the world were known to be contaminated with terrestrial organics. To further my work, I would need “fresh samples.” Unfortunately, carbonaceous chondrites are rare. They fall on average about once every 20-30 years. It is hard to build a career when you are only running one sample every twenty years or so. They were pretty close to being right: the Taglish lake meteorite (another type 2 carbonaceous meteorite) fell in January of 2000, 32 years after the Murchison meteorite. By then, I had been very busy with my career as an ocean chemist. The ocean is big, with lots of places to collect samples for an analytical chemist. No limits to samples there.
WD: Often scientists in controversial fields of study will present one face to the public but then another in private conversation with confidants. Did you witness such a difference with Miller and Bada, where privately they confided doubts to you about how much light their pre-biotic simulation experiments and research actually cast on the origin of life?
EP: Neither Miller nor Bada were believers in God, so for them a natural pathway to the origin of life was the only game in town. Whether the Miller-Urey electric discharge experiment was the actual way life began remained to be seen, but there was never any doubt that a natural pathway would be found someday; whether they would be alive to see it or not was unknown.
They did recognize privately and publicly several obstacles that the natural pathway would need to overcome. The electric discharge process produced racemic amino acids—both D- and L-forms—but living organisms only used the L-form. Likewise, only D-sugars were used by life even though L-sugars also existed. And the Maillard reaction greatly limited the concentration of amino acids in the “prebiotic soup.” As soon as amino acids were formed, they started reacting with sugars and other unsaturated organic compounds. This reaction consumed the amino acids almost as quickly as they were made and severely limited their availability to make proteins.
If one looks at the percent yield of amino acids from the electric discharge process, they are only a minor product. While the world had praised the Miller-Urey electric discharge experiment as a major breakthrough in origin life research at the time it was announced, this promise has faded with time as all attempts to go further and produce proteins and functional enzymes without a major amount of investigator intervention has proved beyond reach.
WD: Your career has focused largely on ocean chemistry and deep-sea instrumentation. How has that research informed or intersected with your understanding of how life might have originated on Earth?
EP: Seawater is an interesting mixture. It contains on average 3.5% by weight “salt.” If one looks hard enough, one can find essentially all of the 92 naturally occurring elements in solution. In addition, there exists 1.2-1.5 mg of carbon per liter of surface seawater as organic compounds.
Again, if one looks hard enough, one can find all of the “building blocks” for all of the biological compounds essential to life: amino acids, nucleobases, fatty acids, sugars, etc. These are produced in free form by the lysing of cells when organisms die. Once the cell wall breaks open, the cell contents are released and hydrolysis of the proteins, nucleic acids, etc. begins releasing everything one needs to build an organism.
And yet, no one today expects a living organism to form spontaneously. Why? Well, bacterial activity is actively consuming most, “re-mineralizing” them to essential nutrients (nitrates, phosphates, carbon dioxide, etc.) for phytoplankton growth. But at the same time, these building blocks are reacting abiotically with each other to form fulvic and humic acids, melanoids, etc.
Unlike the biopolymers, such as proteins, starches, DNA and RNA, which are all composed of compounds from a single class (for example amino acids form proteins and sugars form starches), these geopolymers are an indiscriminate mixture of all the compounds available to react. They lack both a regular structure or function.
Many of the geopolymers are deeply colored, and these are known as melanoids. One of the major sources of melanoids is the reaction of amino acids with sugars via the Maillard reaction. This is the same reaction that consumed most of the amino acids produced in the electric discharge experiments, and it occurs naturally through-out the oceans and on land as well.
So, what does this have to do with the origin of life? Everything. The ocean is the ultimate “prebiotic soup.” All the ingredients for life are there. While bacteria consume most of them in the current ocean, what is not consumed by bacteria we can see reacting in ways that lead away from the biopolymers essential to living organisms and instead lead to the geopolymers, which are of no use to forming living organisms. Moreover, these reactions happen quickly demonstrating that the time window for life to form from the prebiotic soup is very short: millions of years are reduced to centuries or millennia.
Oddly enough, this is not something new I discovered. It was taught by Jeff Bada during his organic geochemistry class: the first week was full of promise for the abiotic origin of life (for example, the Miller-Urey electric discharge experiment produced all the amino acids anyone could want), but by the last week of classes, we were looking at the decomposition and diagenesis of organic compounds in the natural environment by unguided, random chemical reactions. Had we taken the time to pause and think about the implications of what we knew to be happening to organic compounds today, we would have known that what was proposed during the first week of class as a pathway to living organisms was beyond unlikely to the point of being impossible; that random, unguided chemistry goes the wrong way.
WD: What do you think are the minimum criteria for calling something “alive,” and does our current lack of a universally accepted definition impede progress in origin-of-life studies? To what degree is this lack of a universally accepted definition a consequence of trying to redefine the problem of life’s origin to make the problem easier to solve (yet without resolving the actual problem of life’s origin)?
EP: I wish I could remember what they told us in 9th grade biology class for a quick answer. Instead, I must think this through. First off, a living organism has to have an outside boundary: some kind of cell wall or membrane. This membrane serves two purposes: first, it keeps the outside out and the inside in; and second, it has to have an ability to absorb nutrients essential to cellular life, and the ability to rid the cell of biochemical waste.
A living organism also needs to have a metabolic machine: to convert nutrients into useful molecules for the cell, and to make all the necessary components of the cell for reproduction. While plants are capable of making their own energy compounds (sugars) from CO2, H2O and sunlight to drive the cellular biochemical processes, animals need to go and find their nutrition. Thus, a form of locomotion is needed for animals.
Finally, there has to be a form of genetic information: a blue print for making a new cell or a new organism. Otherwise, reproduction would just be a willy-nilly process of cells splitting when they got too big, with some fragments being viable and others not. Life is much more efficient than that.
From what I understand of modern biology on this subject, some folks will agree with me and others will not. Moreover, these “discussions” will be quite heated and very entertaining for the spectators. One will question whether these discussions are based on scientific data or philosophy. Fortunately, I am a chemist and never had to deal with this kind of dissension in our field. The fact that biologists have yet to work this out says a lot about the nature of biological theory in terms of its completeness.
What I have seen is that those working on origin-of-life research have a very general and flexible definition to make for a broad and easy-to-hit target, while those who actually work with living organisms, especially the single cell kind (organisms not researchers), are constantly discovering new things that cells need to be able to do in order to be alive, so the target gets more complex with every new discovery.
In summary, I will say two things: (1) this is a problem for biologists to solve, otherwise those working in the origin-of-life field will not know what their target is; (2) the self-replicating molecular systems that have been developed in the lab are not living. They only “reproduce” as long as enough raw materials are provided, and then everything stops. As such, they are entertaining chemical systems, and nothing more.
WD: What do you see as the most promising current naturalistic hypotheses for how life originated—e.g., hydrothermal vents, surface-based chemistry, RNA world, lipid world, or something else? Are any of these hypotheses in your view well supported in the sense that you see them as live candidates for truly uncovering the details of a naturalistic origin of life?
EP: To be totally candid, none of the current theories are what we might call promising. They all suffer from various fatal errors and as a group ignore the most important issue: a living cell is an irreducibly complex organism. Take any part of it away, and it fails as a living organism and dies. It cannot be built piece-meal. It must be assembled whole, with everything in its proper place, in order to function at all. That means, in addition to needing to gather all the required parts, they must be assembled in the proper fashion in 3D space and done so quickly or else bits and pieces will react chemically and doom the project to failure. So far, the only thing that we know that can make a living cell is another living cell.
As for the various individual theories, here are a few of the fatal errors. Hydrothermal vents do not make organic compounds, they destroy them. One can see this simply by sampling the fluids coming out of the vents, as some have done. The rich assemblage of organic compounds found in the ocean are gone and replaced with simple compounds like hydrogen, the light hydrocarbons (methane, ethane and propane), and some reduced gases like hydrogen sulfide. While a chemosynthetic community now thrives on these gases near the vent, they did not originate there. The vent fluids are simply too toxic and too hot at the source.
Surface based synthesis might yield a few useful compounds, but many compounds with a diverse range of functionality are needed for the first organism. RNA is too unstable outside a living cell to offer much hope of it doing anything in the pre-biotic soup if somehow it was formed (which is exceptionally unlikely). The chance of it coding for useful proteins and enzymes presumes a pre-existing complex biochemical apparatus to transcribe this code and assemble the amino acids. Without ribosomes translating the sequence of information in the RNA and assembling amino acids in the right order into proteins, the information stored in the RNA isn’t going anywhere. This is another case of needing everything in a cell to make a cell at the same time and place, for which random unguided synthesis offers no solution. The odds of it all happening by chance is incalculable due to the vast number of possible outcomes, most of which are unknown at present.
My least favorite theory among all the options is the lipid world. Assuming that one could get a collection of similar chain length fatty acids bonded to glycerol to make triglycerides (which itself is highly unlikely in the pre-biotic soup of randomly generated compounds), then one could form an artificial vesicle (alternatively called a coacervate or liposome) with a lipid bilayer film. What you then have is not much more than a “soap bubble.” There is no interior metabolism, no ion-transport pathways in the “membrane”; it is nothing more than a film-coated droplet. How it would acquire an internal metabolism, etc., is anyone’s guess. But guesses, as entertaining as they might be, are not a scientific explanation of how life arose abiotically.
WD: From a chemist’s perspective, what do you think are the biggest unsolved challenges in naturalistically explaining the transition from simple molecules to the first living systems? Note that we’ll be getting into some of the specific hurdles and challenges momentarily, so in responding to this question it may be best to focus on the big picture.
EP: I can think of 4 unsolved challenges:
The starting conditions on the early earth are at present ill-defined. For the Miller-Urey experiment, a reducing atmosphere was assumed, but recently there are arguments suggesting that the early atmosphere could have been neutral or oxidizing. The lack of consensus on this issue renders a lot of work irrelevant if it is not consistent with the atmospheric conditions that existed on the early Earth.
The identity of the first living organism is also ill-defined. If you don’t know what your target is, it is hard to hit it.
Random undirected chemistry does not yield biopolymers. Organisms need proteins, DNA &/or RNA, polysaccharides, etc. These polymers are uniform in that they are composed of a monomeric class of compounds bound together in very specific ways: proteins are chains of amino acids linked by peptide bonds; DNA & RNA are chains of nucleotides linked by phosphate bridges; polysaccharides (e.g., starch & cellulose) are chains of glucose molecules linked by α-(1,4) glycosidic bonds in starch (amylose) and β-(1,4) glycosidic bonds in cellulose. Random, undirected chemical reactions do not yield these pure polymers. Instead, they yield polymers formed by random condensations of whatever compounds are at hand, producing high molecular weight compounds without a well-defined structure. Examples of this are fulvic and humic acids, melanoids, etc. Their structures are complex, involve monomers from a variety of compound classes and without a common bonding pattern. As such, they exhibit little to no biological activity and store no information.
The biggest challenge of all will be to convince the folks who dream up the various theories for the origin of life to include the impact of competing reactions on their pathways as opposed to writing “just so stories.” It is easy to imagine a world where everything happens just the way you want it to and when you want it to. It is much harder to devise a pathway that achieves the desired results while taking into account all the competing reactions that happen in nature that are working against you.
WD: What role do you think environmental energy gradients—like those near hydrothermal vents—played in prebiotic chemistry? Are these energy flows sufficient to drive the kind of molecular complexity needed?
EP: There is no doubt that increasing the temperature of a reaction makes it go faster. A rather crude rule of thumb for chemical reactions is that for each 10°C increase in temperature, the reaction rate will double (although actual reaction rates vary greatly in this respect). So, the heat from hydrothermal vents will increase the rates of reaction but not its specificity. In other words, reactions at hydrothermal vents can’t focus on one substrate to the exclusion of others. Yet life as we know it requires this sort of focus.
So, if there are forks in the reaction pathway leading to different products or competing reactions, all of these reactions will go faster as well. Likewise, if the concentration of essential chemicals is increased, the rates will increase, but again this will not increase the specificity. For biopolymers (like proteins or RNA/DNA) to form, we need very specific reactions, and the sub-units must be in the appropriate order. Heat and concentration do not provide that. So, the answer to the second part of the question is quite simply, No.
WD: Some researchers argue that informational molecules like RNA are too complex to have arisen without earlier scaffolds. Do you think pre-RNA worlds or simpler polymers could have realistically preceded RNA?
EP: The complexity of DNA and RNA is indeed a problem for undirected chemistry to produce as the number of ways the nucleo-bases, sugars and phosphate can combine is legion but only one way works to make useful nucleotides. However, beginning with a different, simpler polymer to make the origin of the information carrying biopolymers easier creates its own set of problems.
First off, what exactly preceded DNA/RNA? There is no remnant that answers this question, so it is impossible to know for certain what it might have been. Any argument for a specific set of chemicals is merely fanciful speculation. The other fatal problem with this kind of approach is how did those first organisms with a different information molecule switch to using DNA and RNA?
While many computer languages have evolved during recent decades, the switch to a new successor language has always been via an abrupt shift. There was no gradual process shifting from one language to another with a completely different syntax for the various commands. One day we stop using the previous language, install a new compiler (frequently on a new computer with a different CPU, etc.) and begin working with the new language. A gradual transition between languages would be a recipe for chaos. In biological systems, it would be no different. Given the preposterous nature of this suggestion, I think we can dismiss it out of hand.
WD: Let’s now consider some specific biochemical hurdles facing the origin of life. One major hurdle is the origin of homochirality (life using only left-handed amino acids and only right-handed sugars). Like a right- and left- handed glove, these molecules have mirror images of each other, and yet life allows only one orientation of the image, but not the other. What, then, do you make of the leading explanations for homochirality, such as circularly polarized light, mineral surfaces, or amplification mechanisms?
EP: The origin of homochirality (D-sugars, L-amino acids, etc.) has proved to be a difficult problem to solve. The goal needs to be chiral purity otherwise just a single wrong isomer can completely foul the functionality of the biopolymer (protein, DNA/RNA, etc.). Homochirality is always up against racemization, the process by which chiral molecules get mixed with their mirror images (enantiomers). Any such lack of purity among chiral molecules is deadly to life.
All three of the proposed processes to achieve homochirality fail for such reasons. First, they are slow and only achieve a partial enrichment of the desired form. Second, racemization reactions work faster to undo this enrichment. What little progress is made is quickly lost. Third, the racemization rate increases with temperature. So, the condition needed to speed-up other synthesis processes works against homochirality. The source of homochirality remains an unsolved mystery.
WD: Another major hurdle is how to get the right sequential ordering of nucleotides in DNA and amino acids in proteins that will be biologically functional. This is an information problem. How well has it been addressed by naturalistic origin-of-life researchers? Speak also to the problem that linkages between nucleotides and amino acids need not form the chains as we see in life but can show branching patterns, undercutting any biological function as we know it.
EP: Bill, your question has perfectly framed the problem of how difficult it is for a random chemical synthesis to produce a functioning biopolymer as there are actually two issues here. First, as you noted, there is the information problem: getting the monomers in the correct order in either protein or nucleic acid synthesis. But, there is also the chemical problem of getting them bonded together correctly in a linear string of peptide bonds in the case of proteins, and linking the phosphate and sugar back-bone properly in the case of the nucleic acids.
Let’s look at the proteins first as this problem is simpler. Amino acids have two functional groups as the name implies: a basic amine group and an acidic carboxylic group. There is always an amine group on the alpha carbon, that is the carbon next to the carboxylic acid group. A peptide bond can form when the carboxy group of amino acid #1 reacts with the α-amino group in a second amino acid to form a dipeptide. If the carboxy group of amino acid #2 then reacts with the α-amino group of a third amino acid, a tri-peptide is formed and so on.
If this process continues and assuming all of these amino acids are L-amino acids, a biopolymer is formed as happens in living organisms. However, if the process is abiotic, there are several problems that can occur. First, in abiotic syntheses, the amino acids are racemic: half of them will be D-amino acids, and half will be L-amino acids. These “optical” isomers are mirror images of each other, much like our hands are mirror images of each other. The D-amino acids (D for dextro) are the “right-handed” amino acid, and the L-amino acids (L-for levo) are the “left-handed” amino acids. In living systems, only the L-amino acids are used and synthesized.
Another problem for abiotic synthesis is that some amino acids have two amino groups, and some have two carboxylic acid groups. This leads to the possibility that the carboxlic acid group can bind with the wrong amino group (or vice-versa) and thus branches can form in undirected syntheses. None of the proteins in living systems have “branches” as these would impair the proper folding of the proteins into the enzymatic active forms.
And, as if things weren’t bad enough already, there is the problem that in an abiotic synthesis of amino acids, about 27 amino acids are known to be formed (plus 8 more if H2S is added to the gas mixture). Yet life as we know it only uses 20 amino acids. All these additional amino acids were confirmed in some recent analyses of the “soup” formed in the Miller-Urey electric discharge experiment using modern highly sensitive techniques. A recent analysis (2017) of the amino acids from the Murchison meteorite found 30. Of these, many have at least one optically active (chiral) center.
Thus, we have 60 amino acids in total. To keep the math simple, let’s ignore the differences in concentrations of the acids and assume that the chance of randomly selecting the L-isomer of a particular amino acid from this mixture is 1 in 60. Thus, the chances of getting the right sequence of amino acids in a protein of 100 amino acids in length by random chance is 1 in 60100 or 1 in 6.53 × 10177. In the vernacular, that would be considerably less than “slim to none.” But that is just the odds of selecting the amino acids in the correct order; we still have some chemistry to do to combine them in the proper way via peptide bonds. Making proteins via undirected chemical reactions is beyond hard. Based upon these odds, it is impossible.
Similar but more complex problems exist with assembling nucleic acids (DNA & RNA). A DNA molecule consists of two parallel strands of nucleotides linked by hydrogen bonds between the bases. The strands are curved so the molecule resembles a twisted ladder that is called a double helix. Each nucleotide consists of a sugar, a phosphate group, and one of four nitrogenous bases: the purines, adenine (A) & guanine (G); and the pyrimidines, cytosine (C) and thymine (T).
The nucleotides form pairs: A pairs with T, and C pairs with G. So, one strand of the molecule can dictate the sequence of the nucleotides on the other strand. That is the easy part; forming the nucleotides and assembling one of the strands is the difficult part as each nucleotide consists of one of the nitrogenous bases bonded in a precise way with a 5-carbon sugar (deoxyribose) and a phosphate group. In each case, there are multiple ways that these nucleotides can be assembled, but just as in the case of proteins, the linkages must be done in a special and precise way, or it is impossible for the double helix structure to form.
And without that double helix structure, one strand cannot control the sequence of nucleotides in the other. Deoxyribose has 3 hydroxy groups that can form bonds with the nucleobases. Likewise, the nucleobases have multiple places where they can form bonds with deoxyribose: A, C & T have two, G has three. So, there are lots of ways this can go wrong with an unguided abiotic chemical synthesis. Likewise, when forming the phosphate linkages: phosphate must bind with the 5’ hydroxy group on one deoxyribose and the 3’ hydroxy group on the next deoxyribose.
RNA is similarly complex with two added twists: (1) the sugar is ribose which has one more hydroxy group than deoxyribose adding an additional place where either the nucleobase could be bonded in the wrong way, or the phosphate linkage could be wrong. (2) There is no thymine in RNA; instead uracil (U) takes its place.
In either case (DNA or RNA), given the problems of the random synthesis of even a short chain of nucleotides and the obstacles to getting them in the correct order that they would actually code for a working protein, we can easily see that the probability of success is best described as highly unlikely in the utmost sense.
WD: Another major hurdle is how you get carbohydrates and lipid-based cell membranes. These are presupposed by life as we know it. So how could they have arisen by purely naturalistic means? What problems of chemistry needed to be solved for them to arise naturalistically?
EP: Carbohydrates can be formed abiotically by the formose reaction. All one needs is a source of formaldehyde and the appropriate conditions: presence of a base and a divalent cation such as calcium. The first step of the reaction, where two formaldehyde molecules react to form glycolaldehyde, is slow. Thereafter, the presence of glycoaldehyde catalyzes this reaction and forms the basis of an autocatalytic cycle that produces a variety of sugars from 2-carbon sugars to 6-carbon sugars.
However, all is not rosy as there are many pitfalls along the path to ribose and deoxyribose (essential to the formation of RNA and DNA) as well as glucose and fructose (essential to cellular metabolism). Like amino acids, carbohydrates have optically active (chiral) centers, and only the D-form is of use to biochemistry as we know it here on Earth. Since the goal is to describe how life on Earth got started, we need to constrain our discussion to a pathway that leads to the biochemistry we know. Moreover, sugars with 4 or more carbon atoms will have 2 or more chiral centers. In the case of pentoses (like ribose), there are three chiral centers so 8 isomers are possible; and with the hexoses, there are 4 chiral centers and 16 possible isomers. So, while sugars can form easily, only a few of the many possibilities are useful to life.
Meanwhile, there are competing reactions that destroy the sugars. We have already seen that the Maillard reaction of amino acids with sugars yields a variety of melanoid products. And unless the environmental conditions are just right and the pH gets too high, the Cannizzaro reaction will consume sugars in pairs yielding an alcohol and a carboxylic acid. Moreover, high temperatures (like are found in hydrothermal vents) will cause the sugars to dehydrate and char and, yes, this does happen even underwater at high pressures.
So, while the formation of sugars is plausible under prebiotic environmental conditions, so are the many competing and destructive reactions. Hence, it is unlikely that a significant concentration of carbohydrates (sugar polymers) will build up unless the environmental conditions are controlled appropriately. This leads to the question: who or what is controlling these conditions? Random chance is unlikely to get it right.
Meanwhile, lipid-based cell membranes have their own set of challenges. Let’s begin by looking first at what lipids are before we look at how they function in cell membranes. There are several different classes of compounds that are known as lipids, and they serve different functions. A variety of compound types are included in this group including sterols, monoglycerides, diglycerides, triglycerides, phospholipids, and fat-soluble vitamins. They serve a variety of functions in addition to being the structural components of cell membranes, such as energy storage and signaling to control cell metabolism.
Of these types of lipids, the triglycerides are perhaps the simplest to consider and the most important in terms of the formation of cell membranes. As the name suggests, they are a derivative of glycerol where the three alcohol groups are each bonded to a fatty acid. Thus, we have a molecule with a very hydrophilic (water-loving) end and three tails that are very hydrophobic (water-fearing). Depending on the chain length of the fatty acids, triglycerides can be oils, fats or waxes. The longer the chain length, the higher the melting point and the more solid like they become. Organisms living in warmer environments use the longer chain fatty acids, while those that live in cooler climates use shorter chain fatty acids to maintain flexibility of the cell wall.
Where triglycerides are of interest to the formation of membranes comes from the nature of their two ends. The glycerol end is very attracted to water, while the fatty acid tails repel water. When mixed with water under the right conditions of temperature, salinity and pH and with a high enough concentration of triglycerides, they will self-assemble into vesicles (initially called coacervates and more recently referred to as liposomes).
A lipid bilayer is formed from two “mirror image” layers. The outer layer has all of the glycerol ends facing out into the water and the hydrophilic tails facing in. The inner layer is reversed: the hydrophilic tails are facing out and the glycerol ends are facing the inside of the vesicle. In this way, the hydrophobic tails face each other and form a layer that polar substances, like water and salt, have difficulty passing through, and the mutual attraction of the tails stabilizes the vesicle. In this process, a portion of the water solution is trapped inside the vesicle. The size of these vesicles varies, generally in the 2 to 10 micrometer range.
Russian chemist Alexander Oparin would use these vesicles (he called them coacervates) as model systems for his protocells as part of his hypothesis for an abiotic origin of life. Now at first glance, this would all seem promising, but that illusion fades when one looks at the details (the devil is always in the details).
Experiments conducted to investigate the formation of these vesicles have been limited to simple triglyceride solutions: for example, a triglyceride where all of the fatty acids are linear chains, without branching and of a single chain length; usually in the 16–20 carbon range. While this works well in today’s lab experiments, it is an unlikely scenario for early earth conditions where the most common fatty acids are much shorter in length (2–6 carbon atoms) and are frequently branched, making close packing in the lipid bilayer unlikely. Moreover, given the variety of fatty acids available, it is unlikely that a significant concentration of homogeneous triglycerides would form. Instead, a mismatch of triglycerides with 3 different and some branched fatty acids would be most likely. This is not the stuff that has been used in experiments to form stable vesicles or liposomes.
The lipid bilayer is not conducive to either ion transport or nutrient transport. Whatever is in the liquid solution trapped within the coacervate / liposome at formation is well isolated. Diffusion of polar nutrients through the highly hydrophobic “middle” of the lipid bilayer would be extraordinarily slow. Any chemistry contained inside the vesicle would be quickly exhausted. A successful “cell” would need to capture ion, nutrient and waste transport systems from the environment, assuming they were all out there waiting to be utilized, in order to persist for any significant length of time.
While Oparin was confident that these proto-cells would quickly capture a metabolic cycle, a genetic system and reproductive mechanisms, his confidence was based upon the magic of long geologic times, an ocean of organic resources there for the taking and a just-so sequence of everything coming together at just the right time and place. Moreover, the bar for success was very low due to (at the time) a universal lack of understanding of the high degree of biochemical sophistication that we recognize today.
Darwin suffered a similar overconfidence. His vision of a “warm little pond,” in a letter to Joseph Hooker, “with all sorts of ammonia and phosphoric salts, — light, heat, electricity &c. present, that a protein compound was chemically formed, … ” has been the source of much speculation, all of which is rooted in a lack of appreciation for the complexity of a living cell. It did, however, lead to a significant amount of speculation by Oparin, Haldane and others.
WD: Looking back at the Miller-Urey experiment, what do you think its main contribution was, and where did it fall short?
EP: The main contribution of the Miller-Urey experiment is that after decades of speculation (and nearly a century after Darwin’s letter to Joseph Hooker) someone actually did an experiment to test these ideas. Miller did science as opposed to the far easier exercise of speculation. There is an axiom in science, which I learned very early in my graduate school career, that in the absence of data one is free to speculate. Indeed, I remember well a seminar during my first year at Scripps where a well-known scientist (who shall remain nameless to protect the guilty) reached the end of the data he was presenting. He then proceeded to cite the axiom and went on for another 20 minutes speculating on all manner of things one might conclude from his work, if only he had the data. It actually was quite entertaining as we all recognized exactly what he was doing.
What Miller actually did was how science should be conducted. He did an experiment to test an idea and answer a question. No amount of talk or speculative thinking was going to do that. Everything else that came before his work was mere speculation. He was gracious enough to not point this out, as he realized that he had opened a door to a whole new field of research and many more would eagerly follow. And they did.
Where his experiment (and others like it) fell short, was in terms of properly recognizing the significance of the work. The whole world went gaga over his publication. It even made the front page of The New York Times! There was much hyperbole written about how “science” was on the verge of discovering how life began. Years later it was slowly realized that the prodigious ramblings in the popular press were way over-blown. They had been far more confident in their predictions than the results deserved.
It is often said that the journey of a thousand miles begins with the first step. While true, what is frequently overlooked is that you still have 2,246,807 steps to go (depending upon the length of your stride). What I mean by this is that there were many problems that were overlooked in the discussion of his original papers. While the presence of amino acids as products of this experiment was quite significant at the time, that fact overlooked how low the yield was in terms of the amount of the starting materials that were consumed.
The principal products were intractable materials composed of melanoids, tars and carbon soot around the electrodes. This was not the kind of materials biologists and chemists were looking for as they are not components of living organisms. Later it would be shown that the amino acids were racemic, not the pure L-isomers used by living organisms. More recent analyses have revealed a total of about 50 different amino acids were formed, but only 20 are used by living organisms. So, while he did find amino acids, they were not solely the ones living organisms use. There was a lot of chaff mixed in with the wheat.
While Miller was very open and straightforward about these problems, they tend to get over-looked in origin-of-life discussions. There is a tendency to focus on the path to life ignoring all the problems: the competing reactions and sidetracks along the way. This was not Miller’s fault, but it is common behavior among those that argue for a solely naturalistic origin of life, where it is assumed that time and “natural selection” will take care of all the problems. Likewise, this is not a failure of the experimental design. Rather it is a failure to properly understand the true significance of his work. If one views Miller’s experiment solely from a materialistic perspective, where abiogenesis is the only game in town, one will miss the need for a more balanced understanding.
WD: Do you think the field of origin-of-life research has made meaningful progress since the 1950s, or are we still largely grappling with the same foundational mysteries, and if so, why?
EP: Hmmm … interesting question. The answer depends on how one defines “meaningful progress.” We could set the bar low and define meaningful progress as any advance in knowledge, as in “Did we learn something from an experiment even if what we learn is as simple as this way doesn’t work.” In this case, the answer would be yes.
In the decades following the publication of Miller’s early papers, there were many who repeated his experiment with varying mixtures of gases and the addition of minerals or inorganic compounds to act as catalysts. These resulted in the synthesis of similar mixtures of amino acids and other compound classes, but little beyond the various monomers. No biopolymers (such as proteins or nucleic acids) have been found. The key to all of these successful synthesis experiments has been the reducing nature of the gas mixture.
With this in mind, we need to take a second look at the atmosphere Miller used. There are several different opinions on this today. Some argue for a neutral atmosphere (CO, H2, N2 and H2O), some argue for an oxidizing atmosphere (CO2, N2, O2 and H2O). If the early earth did not have the reducing atmosphere that Miller used (CH4, NH3, H2 and H2O), or something very similar, then his experiment is irrelevant to the origin of life on Earth. My personal opinion is that the atmosphere that Miller and Urey chose is the most likely candidate. However, there is currently continued discussion of this issue, for as we have seen, in the absence of data, one is free to speculate. And scientists love to speculate.
On the other hand, suppose we set the bar a bit higher. Instead of “baby steps,” we decide that meaningful progress requires a major advance: something that overcomes the several foundational mysteries unsolved by Miller’s and followers’ experiments.
First up: the problem of racemic synthesis. Life as we know it uses L-amino acids; abiotic synthesis experiments yield racemic (D- & L-amino acids in equal quantities). Attempts to achieve a chiral specificity have yield small enrichments, but never pure D or L forms.
Next, there is the issue of biopolymers: no proteins or nucleic acids have been found to form under pre-biotic conditions. There is an argument that these will come with time, but that argument requires tremendous faith that polymers will form and remain stable under conditions known to promote hydrolysis of the polymers. Time is a poor solution for reversing thermodynamics. One needs a driving force, and none has been found to date.
Finally, there is the issue of competing reactions that either divert the reservoir of biochemical monomers away to undesirable byproducts or destroy whatever biochemical monomers have been made. Finding a way to minimize these processes or to protect the desirable products from destruction would be a major step forward. One of Miller’s early experiments, where the initial gas mixture was occasionally replenished, failed to yield higher concentrations of amino acids. As the reaction proceeded, the concentration of amino acids would plateau and go no higher as the rate of the reactions consuming the amino acids matched the rate of synthesis. As the initial gases were consumed, the synthesis reactions would then slow down, and the concentration of amino acids would then diminish as well.
Other major non-experimental advances that would be meaningful progress would be the determination of a consensus composition of the atmosphere on the early Earth (so the experimentalists would know where to begin and whether the Miller-Urey electric discharge experiment has any relevance) or the identification by biologists of a better description for what the first living organism would be like (so the experimentalists would have a better-defined target). Presently, scientist prefer speculation on these subjects over investigations or consensus building.
WD: What are your thoughts on the search for extraterrestrial life in the context of origin-of-life research? Does finding life elsewhere help us answer how it began here?
EP: Let me begin by saying that the search for extraterrestrial life is a worthy scientific pursuit on its own terms. Asking whether we are the sole inhabitants of this great big, beautiful, awesome, marvelous, frightening and consistently overwhelming universe is a valid question. But it seems to me that should we find evidence of anything from microbial lifeforms to “Klingons and Vulcans” running around the galaxy in their faster than light starships, it is vain to hope that their presence sheds any light on how life began on Earth.
It is a bit like looking at the team standings in the National League and hoping that they tell you how your favorite team in the American League did today. Both leagues play baseball, but the results in one league have essentially nothing to do with how a team in another league does. (At least this was true before they introduced inter-league play.) And so it will be with the existence of life elsewhere in the universe. The two biological systems, though similar in some ways, are totally disconnected in terms of origins. This discovery is far more likely to produce more questions than provide us with any insight to answer the questions that we have about life’s origin here on Earth.
Consider what might happen if someone were to claim that there is evidence of life on Mars. And let us say that this evidence included detailed biochemistry. In this case, we would immediately ask if the Martian organisms used the same 20 amino acids, 5 nucleobases and the same sugars that are essential to life here on Earth. Let us also assume that not only are the same compounds used, but the same chiral isomers: L-amino acids, D-sugars, etc. In this case, we would be immediately confronted with the question: “Did life originate on Earth and somehow jumped to Mars or, vice-versa? We do know that some of the meteorites found in the Antarctic dry valleys are thought to be ejecta from massive meteorite impacts on Mars, so hopping from one planet to another is not wild speculation but has happened.
Whether microbial life could survive such a journey is anyone’s guess. So, instead of a new insight into how life on Earth began, we now are confronted with the possibility that it may not have begun here but came from Mars and we are all descendants of Martians. Moreover, suppose the answer to our question regarding the biochemistry of the Martian organisms was all nos. No common compounds, no common isomers, no similar genetic code. Now we would be confronted with two very separate origins, neither of which has little if any information regarding the other. Thus, as exciting as this discovery might be, or the discovery of life anywhere else in the solar system, it will offer us little new information regarding the origin of life on Earth.
WD: Some critics argue that origin-of-life research is filled with speculative or untestable hypotheses. How do you respond to concerns about scientific rigor in this field?
EP: First off, I would say that those critics are correct. Because so little is known about the environment of the early Earth and its atmosphere, there is great freedom to speculate. While speculation by scientists is not wrong per se, the key is to recognizing speculation for what it is and what it is not. Speculation can be an excellent starting point for designing experiments and testable hypotheses. However, until those experiments are done, it is not science.
All too often, people grasp onto an idea as a possibility without doing the hard work of testing it. When data are lacking, we must be very careful. As Richard Feyman has said, “The first principle is that you must not fool yourself as you are the easiest person to fool.” Miller did an experiment, and it opened up a door to a whole new field of research. What biologists and chemists must do now is to continue to do relevant experiments, being very careful not to stack-the-deck for “success.”
I worry less about all the speculation, as that is easy to spot (there is no data to support the “conclusions”). What concerns me more is that it is easy for chemists to prime the conditions of experiments for success in ways that would not have existed in the pre-biotic world and then attribute that reaction to being a “plausible” abiotic pathway. In order to minimize this form of self-deception, we must be very hard-nosed about calling out all the incidences of investigator intervention.
This does not mean that I think all abiotic / prebiotic experimentation is wrong. There are some interesting papers published. It also means that much of what has been written needs to be taken with a certain amount of skepticism. Let’s not fool ourselves.
WD: Do you think life’s origin was an inevitable chemical consequence of Earth’s environment, or does it strike you as a rare and possibly unique occurrence?
EP: A lot of people do see life as an inevitable consequence of the chemical conditions on the early earth, and NASA spokesmen often express the view that wherever we find liquid water, there might be life. My personal opinion is quite different: life is an exceptionally rare occurrence in our solar system and rarer still in our galaxy. Now I know that this runs contrary to the very optimistic predictions based upon the Drake equation and Carl Sagan waxing poetically about billions and billions of galaxies, but there is good reason to have low expectations.
I have already addressed the many chemical obstacles to an abiotic origin of life even when the conditions are as favorable as we find on Earth. But planet Earth itself is a very rare occurrence in the galaxy. Ward & Brownlee have written a book called Rare Earth where they explain why they think that complex life will be rare in the Universe citing the many physical factors that are overlooked by the more optimistic estimates. It is well worth the read as it is a good counterpoint to all those who argue that life should be ubiquitous.
Likewise, we should look at the Drake equation with great skepticism. One does not have to be a PhD mathematician to recognize that given all the terms in this equation, one can easily “cook the books” to get any result that you wish. Given that there is little to no data to constrain the values of most of the terms in this equation, many feel free to speculate optimistically in favor of life. Here we must remember that speculation in the absence of data is merely speculation and not science.
WD: To what degree is the origin of life a problem of information? Is explaining the origin of life a matter of explaining the origin of the information in living systems? Can this information be accounted for strictly in terms of the underlying physics and chemistry, or does it more plausibly come from a source not reducible to physics and chemistry?
EP: Thus far we have looked at the chemistry problem: how the basic building blocks of biochemistry are made and how are they assembled into biochemically active biopolymers prior to the presence of living organisms via blind undirected chemistry. This is just one side of the coin of abiogenesis. Biopolymers are only functional when their constituent units are in proper order and joined by the appropriate bonds.
Knowing that proper order requires information, and this is the other side of the abiogenesis coin. Neither side can exist without the other, nor are the individual “sides” functional without the other. Unless the two go hand-in-hand, we have made no progress towards the first living organism. This means that information is both essential and central to abiogenesis.
Now some proponents of abiogenesis will argue that getting the right order is simply a matter of time and chance. Bill, you are a mathematician and have written on the incredible number of possibilities for arranging amino acids to make proteins and the probability of achieving one by chance. I won’t try to repeat your arguments here, but I do recommend people read Chapter 4 in your book, The Design Inference, 2nd Edition, to get an idea of the overwhelming number of options and the infinitesimal probability that we get lucky, and all of the essential biopolymers are formed.
Now people will argue that given the tremendous size of the ocean and the time involved, there is a tremendous resource for the many possibilities. I would argue that it does us no good to have the essential proteins scattered about the ocean and millions of years apart. We need all of them simultaneously and in the same spot. And that spot is tiny. A typical bacterial cell is very small. They range in size from 0.2 to 2.0 μm in diameter and 2 to 8 μm in length or 63 atto-L to 25 femto-L (63 × 10-18 L to 25 × 10-15 L) in volume.
So, time and chance are of no help here. Information is needed in order to have functioning cells. So, where might we get this information? Some have argued that it is a consequence of the physics and chemistry of the prebiotic world. This idea, if we stop and think about it, is laughable. Both physics and chemistry are determinant sciences. If you mix two chemicals together, under the same set of conditions, you will always get the same mix of products. There is no chance or contingency here.
Consequently, arguing that the mix of products in the prebiotic soup will change over time and lead to bigger and longer biopolymers is wishful thinking, an act of faith. There is no chemical evidence to back this up. It gives false hope in what some wish for, yet contrary to what we know will happen. Wishes are not science. Abiogenesis needs an external source of information that random undirected chemical reactions can never provide.
WD: Some scientists have expressed the view that we may never fully explain how life began. Do you consider the origin of life a solvable scientific problem—and if so, solvable in what sense?
EP: I think that those scientists are not only right in their thinking—they are courageous to step out and say so. It is hard to imagine how something that happened “millions of years ago,” under conditions that honest scientists do not agree about, and that left essentially no clues as to what happened, could ever be fully explained. Now one day we may find that (a) scientists have finally come into agreement about what the environment on the early life was like, and (b) we may find that biologists have finally determined what the first living organism was and how it survived.
But a complete step-by-step accounting of how we got from (a) to (b) will most likely be impossible to achieve. There are innumerable steps involved, and simply listing (never mind discovering) them will no doubt take more than a lifetime. We may someday discover something as noteworthy as the Miller-Urey electric discharge experiment, that gives us some new insight into the process, and that would be an important achievement.
But fully explaining life’s origin is a synthesis project of immeasurable proportions, and one where operator intervention is strictly disallowed. If we need some investigator to “stir the pot,” even if only once during the whole process, then we have failed to discern an abiotic pathway. And that admission would be tantamount to confessing that we need a miracle, and that is a place where many scientists are not willing to go. For without that abiotic pathway, abiogenesis becomes Genesis.
WD: If you were designing a new research program dedicated to the origin of life, what questions would you prioritize, and what types of experiments would you fund?
EP: I think if I were given the task of designing a new research program dedicated to the origin of life, I would first begin with a symposium to gather together prominent researchers in the field to discern where we currently stand on this issue, what the major challenges are, and whether there are any promising new ideas to explore. I would call the symposium “Discovering the Origin of Life: 75 years after the Miller-Urey experiment.” With the sub-title: “Have we made any progress and what do we do next?”
I would invite three or four people working in this area to join me and form a steering committee. We would come up with a series of sessions to consider the various aspects of abiogenesis, such as:
Starting conditions. What was the environment of the early Earth really like? Reducing atmosphere or oxidizing?
What is a likely candidate for the first living organism? What is the minimum biochemistry it needs to have.
Origin of chiral specificity: the why and how of left-handed amino acids and right-handed sugars.
Formation of biopolymers: chemistry and sequences.
Competing reactions: where the chemistry goes amiss and how to avoid ignoring the problem, so we don’t fool ourselves into thinking things are easier than they really are.
Investigator intervention: how much if any is allowed?
I would have proponents and skeptics on my steering committee so we could select speakers both pro and con on each of these topics. We would invite both established scientists and graduate students to attend. And we would encourage folks to “argue it out” (politely and courteously, of course) so that a consensus could be reached on each topic. During the discussions, emphasis would be put on what data do we have to support each and every viewpoint vs theoretical arguments rooted in various ideologies.
The goal of the symposium would be to get clarity on what our starting point should be and where we need to get to—questions 1 and 2. We would also evaluate whether any progress has been made toward answering questions 3 to 6. Based on the presentations and the discussions, I would hope that an honest appraisal would be made regarding progress during the 75 years since Stanley Miller first published his results.
I would hope in this symposium that we did not take the classic fallback position where we pretend to have made progress so we can ask for more money to do further research. If we were brutally honest with the science or lack thereof, we would know what areas are promising to pursue, or whether it is time to admit that we have been fooling ourselves all these years and are no closer to unraveling life’s origin than we were in 1953.
WD: Have your decades in the field shifted your view on whether life’s emergence was a natural, unguided process? Do you see intelligent design as a viable scientific alternative to explaining life’s origin naturalistically? If so, how do you understand intelligent design as contributing to origin-of-life research.
EP: Has my view on whether life’s emergence was a natural, unguided process shifted with time? Of course. One starts out young and naïve. I believed pretty much everything I read in books and was taught in class. But as I learned more, I developed a healthy skepticism and learned to think for myself. Not so much in high school, but more so in college and graduate school. It was all part of being a scientist: you learn to not always take everything at face value. Instead, I learned to ask questions: Do the conclusions fit the data? What is the evidence for this? And so forth. Pretty soon, it becomes second nature: You listen and read with a sense of skepticism and demand that the speaker or author(s) support their case with evidence, not just a good argument to go along with the prevailing theory.
Over the course of my career, biology and biochemistry got more complicated and my understanding of what could happen naturalistically got more and more limited. Random, unguided chemistry could no longer do what needed to be done. In fact, the more I learned about diagenesis (the processes that happen when organic matter is released into the environment following the death of an organism), the clearer it became that unguided processes were headed in the wrong direction. Something entirely different was needed.
Intelligent design offered a different way of looking at the problem of life’s origin. Instead of trying to come up with a “natural” or random & unguided process to build and organism, one can look at the organism from the point of view of life as a well-designed, programmed and efficiently operating system. This gives one a totally different appreciation for living organisms. They are no longer the accidental products of natural selection operating on whatever random mutations just happened to produce. Rather, they are the product of an incredible intentional marvelous design. Only then do the elaborate and interlocking biochemical processes make sense.
Intelligent design flips the origin-of-life question on its head. We no longer need to focus on the myriad of steps to go from inanimate chemicals to a living system and argue over details that we may never know for sure. Instead, we can develop an appreciation for the wonderful gift of life we have and begin to ponder who the intelligent designer might be. We go from a purely material accident to wonderful intent. And that perspective changes everything about origin-of-life research.
WD: Origin-of-life research can be controversial. Add intelligent design into the mix, and discussions can become explosive. Can you offer some insight for dealing with scientific controversy, especially in public contexts (rather than merely in print)?
EP: I did not have to personally deal with any public controversy regarding my thesis research, but I did witness a very interesting and public exchange that almost got very ugly. It was during my third year at SIO — I had already picked my thesis topic and passed my qualifying exam, so I was well on my way working with Jeff Bada and Stanley Miller.
The UCSD Chemistry department had invited Edward Anders of the University of Chicago to give a series of lectures on his research related to the early history of the solar system, the origin of the elements and the origin and nature of meteorites. The first lecture was held in a large auditorium on the main campus with over 300 people in attendance. Dr Anders gave a wonderful lecture on the origin of the solar system and the elements via nuclear synthesis in stars.
The lecture was very well received until the Q&A session began. Immediately, Hannes Alfven (Hannes Olof Gösta Alfvén) leapt to his feet, walked to the front of the room with several pages of notes and gave a 3–4 minute rebuttal of Anders presentation. The audience was stunned, Anders did not know what to say, the moderator did not know what to do and there was an incredible awkward moment of silence. You could cut the tension in the air with a knife.
At this point, Gustaf Arrhenius waved his hand to ask a question and the moderator quickly called upon him. Arrhenius stood up and began by saying, “Actually, you both are wrong!” The audience immediately broke out into laughter; the tension was cut and civility returned to the room. Arrhenius then admitted that he didn’t think his comment would be that funny. It was the perfect antidote to a tense situation. He did go on to make a few comments about where he thought both Anders’ and Alfven’s theories might be lacking, but then he said that was OK. It meant that we did not know everything, that there was still work to be done and graduate students would still have topics for their theses.
The lesson that I learned from these exchanges is that there is a proper & polite way to deal with controversy and there are other less effective ways of discussing disagreements. Arrhenius had given us all an excellent example of how to be a scientist.
WD: Finally, if you could offer one piece of advice to a graduate student entering the origin-of-life field today, what would it be?
EP: Run! Run as fast as you can and as far as you can. Find something else you can be passionate about and have fun studying it.
Now that is what I’d like to say, but it will most likely not be taken well. In fact, it is not very good advice because it does not honor the person asking the question. Instead, let’s take their desire to study the origin of life seriously and ask them several questions to help them understand the nature of their decision and the difficult path that lies ahead:
Are you willing to enter a field where even the simple question of where we begin is unknown? Miller was lucky as he had Harold Urey tell him it begins with a reducing atmosphere. Since then, others have argued for neutral or oxidizing atmospheres. Sometimes, they argue based upon evidence, sometimes they argue for a different atmosphere that is conducive to their favorite pre-biotic reaction without any evidence that those conditions occurred. It is hard to succeed when you don’t know where to begin.
How are you going to know if you have succeeded? The nature of the first living organism is also unknown and subject to much speculation. If you don’t know what your target is, how are you going to know if you hit it?
Beware of investigator intervention. It is easy to make progress on building biopolymers or whatever by carefully manipulating the conditions. However, we already know that scientists and their graduate students can do biochemistry and make biopolymers, etc. There will be no accolades for that. You will need to do it using only unguided reactions under what can be judged as reasonable pre-biotic conditions. There can be no “stirring the pot” to help things along!
Be ready for severe criticism. There are a lot of people working in this field already and they have very different theories and pet mechanisms of which they are highly protective. So, no matter which group you choose to join or whose ideas to follow, there will always be more detractors than allies. And when it comes to criticizing a competitor, scientists can be very critical, and sometimes (not always) they can be quite nasty doing so.
Finally, if after considering all of these questions the person still wants to pursue a career studying the origin of life and they feel very passionate about it, then I will wish them well and hope that they find some measure of success. They just might find something interesting. Science and the universe still have their surprises.
WD: I’m deeply grateful to you, Ed, for all your care and effort in giving this detailed interview!
Reading the details of a scientist's journey is encouraging and informative. Thanks for sharing the conversation. Having a background in aquatic ecology, specifically, limnology, made the exchange especially interesting.
Why did it end with "Finally, ther" ?