The Krebs citric acid cycle is a complex process that occurs in the mitochondria of most of the cells in our bodies, resulting in the production of molecules like ATP (Adenosine triphosphate) which are the fuel that sustains life. Without the tiny ATP molecule our bodies would shut down just like an engine that had run out of gasoline.
Amazingly, the extremely complex series of reactions leading to the production of ATP occurs in even primitive bacteria so it must have evolved very early on in the history of life and therefore very rapidly, which is astonishing to think about, given the enormous complexity of the cycle:
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| The Krebs Citric Acid Cycle |
The naturalistic view is that the evolution of this cycle occurred without any direction, without any guidance, without any goal in sight, that all the pieces were assembled from pre-existing chemicals, arranged by random trial and error through the mechanism of genetic mutation and natural selection. It's an almost miraculous defiance of probability.
This is not to say it didn't happen that way. It could have, and lots of very intelligent people think it did, even though when they write about it they can't help but use telic language (i.e. language that implies a goal or purpose).
Consider this excerpt from a well-known 1996 paper:
During the origin and evolution of metabolism, in the first cells, when a need arises for a new pathway, there are two different possible strategies available to achieve this purpose: (1) create new pathways utilizing new compounds not previously available or (2) adapt and make good use of the enzymes catalyzing reactions already existing in the cell. Clearly, the opportunism of the second strategy, when it is possible, has a number of selective advantages, because it allows a quick and economic solution of new problems.Thus, in the evolution of a new metabolic pathway, new mechanisms must be created only if ‘‘pieces’’ to the complete puzzle are missing. Creation of the full pathway by a de novo method is expensive in material, time-consuming, and cannot compete with the opportunistic strategy, if it can achieve the new specific purpose.We demonstrate here the opportunistic evolution of the Krebs cycle reorganizing and assembling preexisting organic chemical reactions....Once the design of a new metabolic sequence is achieved, a refinement of the pathway may be necessary, and then, a further optimization process will move the design toward maximum efficiency by reaching optimal values of rate and affinity constants of enzymes. Such an optimization process as a result of natural selection is also a well-documented feature of biological evolution.... the design of the pentose phosphate and Calvin cycles can be mathematically derivedby applying optimization principles under a well-established physiological function.... By considering the first stages in the history of life, we may attempt to determine logically under what conditions the Krebs cycle was organized and what its first purpose was.
This language is of course intended to be metaphorical, but the point is that it's exceedingly difficult to describe the origin of pathways such as those comprising the Krebs cycle without comparing it to an engineering problem solvable by intelligent agents. In fact, the metaphorical, telic language often employed by scientists serves, perhaps unintentionally, the purpose of obscuring how improbable it is that this cascade of chemical reactions and others like it would have somehow arisen by chance genetic mutations and natural selection.
Here's another metaphor:
Suppose a card dealer shuffles a deck and lays the cards out on the table one at a time. We're assuming that the cards already exist and don't have to be manufactured (some of the chemicals in the Krebs cycle did not already exist before the Krebs cycle evolved).
Let's also assume that the dealer has a goal in mind (although, of course, nature has no goals in mind). The dealer's goal is to obtain a sequence in which each suit from ace to king appears in the order hearts, spades, diamonds, clubs.
Let's further assume that whenever he fails to get the ace of hearts as the first card he reshuffles the deck and starts over. When he does get an ace of hearts he then lets it lay and tries for a two of hearts. If he doesn't get a two of hearts on the first attempt he reshuffles the entire deck and starts over. And so on.
How long would it take to get the sequence he has in mind? This is a bit like the difficulty confronting the chance evolution of a complex system like the Krebs cycle, but with the evolution of the Krebs cycle, at least the naturalistic version, there's no goal in mind, and indeed no mind at all. Just random trial and error, chemicals bumping about, until something useful is hit upon and somehow retained and eventually added to.
Of course, an intelligent card dealer, even a child, can order the cards in the desired pattern, but desired patterns, goals, and certainly intelligent dealers, are prohibited in naturalistic explanations.
The naturalist declares that he relies on science and not on faith in non-natural intelligent agents, but it seems to me that it should take a lot more faith to believe that the Krebs cycle could have arisen with no intelligent input to guide its development than to believe that it arose through the intentional agency of a biochemical genius.
