Probability as an Objection to Abiogenesis and/or Evolution
by, 16th June 2012 at 04:45 PM (2415 Views)
Youíve seen this argument: that the chance of a protein, or DNA sequence, or some biological structure occurring is so low that it could not have happened without guidance or intervention. That life had to be created somehow Ė whether designed or miraculously. Itís an argument that goes back more than 50 years, and has been embraced by the likes of very intelligent scientists, including Fred Hoyle. Itís one of the most common arguments currently used by proponents of creationism and intelligent design Ė including Dr. Michael Behe and William Dembski.
The problem is, this argument is flat-out wrong. So wrong, in fact, that thereís a name for it: Hoyleís fallacy. http://en.wikipedia.org/wiki/Hoyle%27s_fallacy
Let's further clarify on why any argument about a modern protein occuring "by chance," is wrong.
(1) Modern proteins - even in the simplest bacteria - are the product of billions of years of evolution. They are not representative of the earliest life-forms, much less the earliest self-replicating systems. This means that any statistical argument which says that the chance of hemoglobin, for example, occurring by chance is vanishingly small is actually irrelevant.
(2) Calculations like those used to suggest that a 100 amino acid long protein has a brute-force chance occurance of 20^100 (or 1 in 7.9x10^131) involves a couple of key assumptions.
The first basic assumption is that only one of the 20 naturally occurring amino acids is fit for a particular sequence position (this is why it's 20^100). This is not true. Most functional proteins are highly tolerant of point mutations, even to amino acids of entirely different side-chain character (e.g., in many proteins one can substitute alanine for a glutamic acid with absolutely no loss of function). In other words, 20^100 is a rigged calculation that will automatically provide the lowest possible probability rather than a more realistic probability.
The second basic assumption is that only a single amino acid sequence can accomplish a given biological task. Now, this is a far more complex point than saying that systems that do a particular job are often conserved (and that point is true). Rather, Iím saying that this assumption involves a quite literally backwards way of looking at how life evolved. It assumes that out of all possible amino acid sequences, the only one fit for a biological function that is being performed in modern life forms is the one that is performing said task in modern life forms. This is not true. Itís a backwards way of looking at it, in that itís a top-down approach. Itís far more accurate and correct to say that a particular structure, once assembled, performs a particular task that life may (or may not) take advantage of.
(3) The probability ascribed is brute-force-chance only; it does not take into account physical laws, the favorability of polymer formation, quite literally any number of tens to hundreds of scientifically valid objections. In other words, itís taking a complex process and attempting to say that said process is unlikely by likening it to rolls of so many dice. Itís inaccurately and incompletely modeled. Furthermore, such calculations generally assume sequential trials, rather than parallel trials Ė in other words, one coin flip at a time, rather than a billion coin flips at once. Sequential trials are not an accurate model of processes involving billions of atoms and molecules (even in a very tiny sample).
(4) The argument is essentially irrelevant anyway, now that there are multiple studies which show that simple self-replicating molecules can and do form in the laboratory and under early earth conditions. In other words: life forming ďby chance,Ē (and by that term, I mean without direct supernatural intervention or intelligent agency; according only to physical laws as we understand them) is looking ever and ever like a very probable occurance. Self-catalytic (and indeed, "evolving,") libraries of chemicals are really rather simple to make.
Sources are provided by point above.
(3) See first source from (2).
(4) Note that this is a tiny sample of the literature. Let me know if any links donít work (Iím not at work today, and so cannot access most of the articles from home). These are relevant to both auto-catalytic systems created in the lab and under early earth conditions, and modeling of such systems proposed to have existed on the early earth.
Design and synthesis of functional polymers by in vitro selection - Ito - 2004 - Polymers for Advanced Technologies - Wiley Online Library
Selection and Amplification of a Catalyst from a Dynamic Combinatorial Library - Brisig - 2003 - Angewandte Chemie International Edition - Wiley Online Library
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