Life Evolving

Unfortunately, the book delivers neither.

As another reviewer pointed out already, De Duve divulges the reader into the basics of cell biology; a nice introduction of life chemistry, proteins, RNA, DNA, enzymes and such.

De Duve then spends few chapters on paving the way from a pre biotic world to one that is dominated by protocells. He believes that proteins are a by-product of RNA and therefore RNA must have preceded proteins. Judging by the complexity of RNA, he postulates that peptide bonds _somehow_ formed among amino acids with the help of what he calls "multimers" (amino acids among other things), and those short peptides could have played the role of a primitive catalyst.

What De Duve fails to provide through out his book is data + examples. To convince any reader with the possibility of such event, common wisdom dictates a minimum amount of experimental data to support the "building" blocks of his hypothesis.

In 1997, Ghadri group synthesized a peptide ligase. That is, a self-replicating 32 amino-acid long peptide. It is the constant lack of evidence that makes Du Duve arguments weak.

Then he says that ATP and other NTPs _somehow_ arose, and the discussion for their "existence" is beyond the scope of the book. Then our catalyst peptide forms an RNA-like structure from ATP and others. Then he says that many bases were initially bound, not just A, U, G, and C. But once we had a "rare" RNA with A, U, G, C, it is _somehow_ more stable and more reproducible. De Duve does not really discuss why he believes this is the case, other than it must be because this is what we have now.

In one occasion, De Duve says "Admittedly, this is all hypothetical. But the hypothesis rests on undeniable foundations and has the advantage of suggesting experimental approaches". He made it clear on several occasions than many areas of pre biotic chemistry lack experimentation despite their significance in origin-of-life research. After suggesting an experiment, he concludes "This is what I would do if I were 20 years younger".

De Duve then goes on to explain how the RNA led eventually to proteins (RNA attaches itself to some amino acids, and using the RNA itself as a catalyst, we form protein). And that once we had proteins, life needed cells at that stage to compete and protocells were created. The RNA made proteins, and RNA that made better proteins for the cell survived and got duplicated. The cell at this has some rudimentary membrane, and can replicate itself via division.

What he skipped is how such membrane forms, why it forms, and how the division process in this protocell exactly takes place.

I really wished that De Duve paid more attention to such critical details. Different people might read the book for different reasons, I read it for the goal of gaining an understanding on abiogenesis. Being a strong believer in abiogenesis myself, I was quite enthusiastic when I began reading the book. However, skepticism over Duve's take on abiogensis kept growing as I read more chapters.

Unfortunately, I lost faith in his approach to this critical issue.

De Duve gives a great review of just how cells work at the molecular level. There is adequate depth without getting bogged down in details. What I really wanted to see was his explanation for the origin of life. De Duve proposes that

Abundant triphosphates somehow arose to provide energy
Prebiotic peptide catalysts somehow arose
Myriads of different RNA-like molecules somehow formed from phosphates
"Rare true-RNA" molecules evolved by Darwinian evolution
RNAs began to make proteins out of the abundant amino acid soup
The RNAs began to make cell walls
The genetic code for specific proteins arose via Darwinian evolution
These very short RNA chains grew tremendously longer via Darwinian evolution
DNA developed from RNA to form protocells
The protocells evolved via Darwinian evolution until they became the first living cells

The key to his proposal is molecular selection. "This mechanism, it must be emphasized, represents at the molecular level exactly that imagined by Darwin to account for biological evolution". In other words, the way to get around the incredible odds of accomplishing each of the proposed steps to life listed above is by having non-living molecules competing with each other. The winning molecules then advance to the next level of competition.

De Duve is rather less than kind to those who disagree. He is distressed that many intelligent people, even scientists, do not agree that this is a plausible explanation to the origin of life. As one with a background in the earth sciences, I am one of the skeptics. My major problem is that he seemingly ignores data from other scientific disciplines. His premise depends on assumptions that are either wrong or improbable at best.

His proposal requires a benign chemical environment with a rich prebiotic soup from which the peptides, RNAs, and proteins could form. Geochemists and planetary physicists have conclusively demonstrated that this soup simply didn't exist. The neutral atmosphere of the early earth could not form prebiotics. In addition, there was sufficient photogenic oxygen in the atmosphere and radiogenic (radiation-induced) oxygen in the oceans to destroy them if they did form. No "prebiotic soup" has ever been found, although "post-biotics" are extremely common. What does exist in abundance are deposits of poisonous heavy metals and rare-earth elements. The early ocean more closely resembled the deadly effluent from a toxic waste dump than the prebiotic soup De Duve needs. Entire industries exist to mine these materials which were once poisons dissolved in the early oceans.

De Duve proposes that prebiotic materials were delivered to the Earth from outer space. Small amounts of nucleic acids have been found in some meteorites, and comets often contain some carbon compounds as well. In reality, the volume of chemicals is small, but the energy release is not. For example, the Shoemaker-Levy comet which struck Jupiter in 1994, probably contained hundreds of tons of organic compounds. This is the proverbial "drop in a bucket" in terms of getting a meaningful volume of prebiotics into the ocean. However, the impact event was roughly 100 million megatons of TNT. This is ten thousand times the power of all of mankind's nuclear weapons combined. We would all be dead if this impact had occurred on Earth.

Another problem occurs in obtaining concentrated baths of organic compounds. The scenarios De Duve mentions are Darwin's "warm little pond" and Stanley Miller's "drying lagoon". These are physical impossibilities on the early earth, where tides were measured in hundreds of feet and wind speeds were measured in thousands of miles an hour. Think of the movie "Perfect Storm" and consider that the weather never got that nice 3.9 billion years ago! There is no plausible mechanism available to generate a concentrated bath of prebiotic compounds in such an environment.

The last several chapters delve into esoteric astronomical subjects far from De Duve's area of expertise, including life on other planets. Large numbers are quoted, but there is little discussed in the vein of cause-and-effect from which a meaningful statistical calculation could be made. He acknowledges that the physical properties of the universe exhibit evidence of incredible precision which allows life to exist. Inconceivably tiny deviations in a number of parameters would make life impossible. This "anthropic principle" has led many formerly atheistic or agnostic scientists to a belief in God. I know one radio-astronomer who wrote "Astronomers who do not draw theistic or deistic conclusions are becoming rare", while his atheist collegue complained that his fellow astronomers are rushing off to join "the First Church of Christ of the Big Bang." De Duve apparently prefers the explanation that there are an infinite number of universes, perhaps even evolving via natural selection, and ours is the lucky one.

De Duve's final appeal is that "something positive must be proposed that can eventually replace the myths propagated by religion." God does not exist, but we need "spiritual guides" to provide ethics and morals. "The religious feeling is deeply embedded in our nature, probably carved into it by natural selection"

I enjoyed De Duve's excellent description of cellular biology. However, I found his proposed mechanisms for the origin of life unconvincing and unsupported by actual chemical pathways. He ignored the hard evidence from other scientific disciplines that render his explanations highly implausible. His premise that science has demonstrated naturalistic explanations to how the universe, the earth, and mankind got here requires more faith than I can muster. I remain skeptical, and tend to agree with the astronomers, who are finding increasing evidence of "something else behind it all".

However, evolutionary convergence shows that the history of life is not as contingent as some critics of de Duve's positions would argue. Quite surprisingly, the author does not discuss any cases of molecular convergence in Life Evolving. The small, but very revealing, list of known examples includes the independent development of biosynthetic pathways for molecules such as lysine or the imizadole moiety found in purines and histidine as well as the polyphyletic origin of several nonhomologous classes of nucleic acid polymerases. With only one example of biology (Earth's own) we cannot calculate probabilities, but the search for extraterrestrial life may assist us in evaluating the evolutionary odds of life and consciousness. The idea that life on Earth is the result of a miracle or of a rare chance event has been replaced by an evolutionary narrative. Still, as William Blake wrote in There Is No Natural Religion, "Reason, or the ratio of all we have already known, is not the same that it shall be when we know more." The discovery of dozens of planets orbiting nearby stars and the prospect of searching for compounds of possible biological origin in their atmospheres suggest that in the not-so-distant future we may have more factors to consider when addressing the issues de Duve raises.

Whether or not one agrees with de Duve's strong statements, Life Evolving forces the reader to avoid intellectual complacency and to articulate one's own arguments to effectively address his position. These are, in themselves, major reasons to appreciate the book.