Evolution Icon Evolution

Leslie Orgel: Metabolic Origin of Life “Unlikely”; Complexity Requires “A Skilled Synthetic Chemist” (Part 2)

In Part 1 I discussed the eminent and late origin of life theorist Leslie Orgel’s criticisms of theories that self-sustaining metabolic pathways could spontaneously come into existence on the early earth and evolve into life. Orgel’s was skeptical that this could occur because “the chance of a full set of such catalysts occurring at a single locality on the primitive Earth in the absence of catalysts for disruptive side reactions seems remote in the extreme.” Indeed, according to Orgel, the type of complexity we normally find in the metabolic pathways of life require “a skilled synthetic chemist.” But what if we assume that such pathways could come into existence? Even if such pathways existed, they would still be far from life as we know it, for they would somehow have to evolve into DNA-based life. Orgel thus also takes aim at the claim that such metabolic pathways can evolve into molecules carrying genetic information. As usual, the problem is that these vague explanations fail to account for the origin of the “information content” in life:

Genetic materials are then seen as late additions to already fairly complex evolved life forms. According to this view, a genetic material merely adds stability to systems that already have a substantial “information content.” It is not easy to translate these intuitions into schemes that can be examined critically, but I will try.

(Leslie E. Orgel, “The Implausibility of Metabolic Cycles on the Prebiotic Earth,” PLOS Biology (January 2008, Volume 6(1):e18).)

According to Orgel, such metabolic pathways have little apparent reason to evolve into genetic molecules, because they “d[o] not seem capable of evolving in any interesting way without becoming more complex” and the proposed explanations fail to “explai[n] how a complex interconnected family of cycles capable of evolution could arise or why it should be stable.” The problems faced by evolving multiple metabolic pathways are the same as the problems faced by those trying to evolve a single metabolic pathway:

Given the difficulty of finding an ensemble of catalysts that are sufficiently specific to enable the original cycle, it is hard to see how one could hope to find an ensemble capable of enabling two or more.

Orgel goes on to explain that until there is empirical evidence that a family of metabolic cycles could evolve–systems that do not require highly specific or efficient catalysts–“acceptance of the possibility of complex nonenzymatic cyclic organizations that are capable of evolution can only be based on faith, a notoriously dangerous route to scientific progress.” He concludes his article with a call to provide more detail about how metabolic origins of life scenarios took place:

The lack of a supporting background in chemistry is even more evident in proposals that metabolic cycles can evolve to “life-like” complexity. The most serious challenge to proponents of metabolic cycle theories–the problems presented by the lack of specificity of most nonenzymatic catalysts–has, in general, not been appreciated. If it has, it has been ignored. Theories of the origin of life based on metabolic cycles cannot be justified by the inadequacy of competing theories: they must stand on their own.

(Leslie E. Orgel, “The Implausibility of Metabolic Cycles on the Prebiotic Earth,” PLOS Biology (January 2008, Volume 6(1):e18).)

The ability to create an information-carrying genetic molecule is not resolved According to Orgel, “solutions offered by supporters of geneticist or metabolist scenarios that are dependent on ‘if pigs could fly’ hypothetical chemistry are unlikely to help.”

At the beginning of this series I recounted that last year, Robert Shapiro, critiqued various origin of life scenarios, but proposed metabolic pathways as an alternative explanation of the source of life. Now the eminent origin of life theorist Leslie Orgel has posthumously shown that such explanations are presently found wanting. Different hypotheses are being tossed about by different scientists, but scientists are finding great deficiencies with each of these various hypotheses. In my view, perhaps the problem for all of these hypotheses is that life did not originate via blind chemical processes, because the language-based specified and complex information contained in DNA is precisely the type of code or language that, Stephen C. Meyer recognizes, “invariably originate[s] from an intelligent source, from a mind or personal agent.”


Casey Luskin

Associate Director, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



Leslie Orgelorigin of life