Unsolved:Alternative theories of quantum evolution
- For the theory more commonly associated with this name see: Quantum evolution.
Quantum evolution is the hypothesis that quantum effects can bias the process of mutation towards adaptive genetic variation.[1] The first publication on this subject, which appeared in a peer review journal, is by Vasily Ogryzko.[2] In 1999, biologist Johnjoe McFadden and the physicist Jim Al-Khalili published an unrelated model of adaptive selection for lactose metabolism in non-metabolizing E. coli.[3] in which they proposed a mechanism based on enhanced decoherence of quantum states that interact strongly with the environment. McFadden published his book Quantum Evolution in 2000.[1]
Background
The "classical" Darwinian model of the evolution of cells is based on a mechanism whereby cells individually undergo mutation, with the process of natural selection then culling out those mutations which are less beneficial to the organism. Quantum evolution is an attempt to provide a theoretical mechanism which would skew these random mutations in favor of some outcome beneficial to the cell.
It should be stated at the outset that this hypothesis would only be useful if indeed there were evidence that some sort of adaptive mutation occurs - in other words, if there were experimental data showing that the classical model of random mutation is lacking, and that certain mutations are "preferred" (occur more frequently) because they confer a greater benefit to the organism. This is a controversial subject in and of itself; a plethora of papers have been published on the enigmatic phenomenon of adaptive mutation and the issue of their origin and mechanism remains unresolved. To date there is no such generally accepted mechanistic explanation of adaptive mutation.
A mechanism proposed by quantum evolution is to imagine that the configuration of DNA in a cell is held in a quantum superposition of states, and that "mutations" occur as a result of a collapse of the superposition into the "best" configuration for the cell. The proponents of this approach liken the operation of DNA to the operation of a quantum computer, which selects one from a multitude of possible outcomes.
Several problems need to be overcome for this hypothesis to be consistent with our current knowledge of quantum physics. Most importantly, the state of quantum superposition must last long enough to allow the DNA to do its normal job (produce RNA). Without this, there would be no way for a comparison of the outcomes of various mutations to occur and thus no basis for the system to bring about adaptive mutation. Protein formation occurs at a rate of on the order of 10,000 times a second (10−5 seconds per protein formed). However, DNA is not translated directly into protein, instead DNA is transcribed into a messenger RNA and this RNA copy is then used for protein biosynthesis. A gene is therefore never directly linked to its protein product, making any possible mechanism for signal transmission between a protein and the DNA that encodes it hard to imagine without action at a distance.
Although some have, by analogy to the technique of NMR imaging, posed state coherence times as long as half a second,[1] this analysis has been challenged by Matthew J. Donald[4] (but see also McFadden and Al-Khalili's rebuttal,[5] and Donald's response [6]), and coherence times on the order of 10−13 seconds seems to be a much more realistic outcome. This latter time would be far too short by many orders of magnitude for the protein formation required for a superposition of quantum states to affect mutations.
However recent evidence indicates that quantum coherence of electrons and protons does indeed occur in some (maybe all) enzyme reactions in living cells, such as those involved in photosynthesis [7] and may even be responsible for the huge catalytic enhancement of reaction rates provided by enzymes.[8]
If this hypothesis were indeed true, one could further speculate that a similar, more robust process could explain observed phenomena such as the apparent "jumps" in the fossil record as adaptive mutations on an even larger scale; this would require even longer periods of state coherence than those described by McFadden et al.[1] yet this has not been proposed by any of the advocates of quantum evolution who have limited their speculations to molecular processes.
Science fiction writer Greg Egan, in his book Teranesia, posited a similar mechanism, whereby large adaptive mutations occur in multiple species under the aggressive quantum mechanical influence of a new protein.[9]
Controversy
A primer on quantum mechanics (such as from David J. Griffiths' "Introduction to Quantum Mechanics") suggests that the very notion of having a molecule choose a state over all others purely based on an exterior system, with no simultaneous effects on said molecule, is completely contrary to how quantum mechanics works. Quantum mechanical states are dependent on things like energy and other physical phenomena. Furthermore, imposing a viewpoint that one outcome is best implies that a best configuration needs some formal definition that is independent of mentioning organism lifespan, reproductivity, etc. (as quantum mechanics does not depend on those things) and that the best configuration does depend on things such as energy levels, perturbations to the molecule, and similar things. When all of these are taken into consideration then the best state would seem to yield a truly random mutation as per what is perceived by humans as evolution.
However, the theory, at least that proposed by McFadden and Al-Khlaili,[10] did not propose that certain states are identified as 'best' by the quantum system but only that certain states interact with the environment more strongly than other states and thereby promote more rapid decoherence. For a starving cell, these more interactive states are those DNA states that encode mutations that allow the cell to grow.
See also
References
- ↑ 1.0 1.1 1.2 1.3 McFadden, Johnjoe (2000). Quantum Evolution. HarperCollins. ISBN:0-00-255948-X; ISBN:0-00-655128-9
- ↑ Ogryzko, V. V. (1997). Biosystems 43, 83-95 [1] [2] [3] [4] [5]
- ↑ McFadden J. J. and Al-Khalili, J. V. (1999). A quantum mechanical model of adaptive mutation. [6][yes|permanent dead link|dead link}}] Biosystems 50, 203-211
- ↑ Donald, Mathew J. (2001). A Review of Quantum Evolution
- ↑ McFadden, Johnjoe; Al-Khalili, Jim (2001). "Comment on Book Review of 'Quantum Evolution' (Johnjoe McFadden) by Mathew J. Donald". arXiv:quant-ph/0110083.
- ↑ [7] "A response to Johnjoe McFadden and Jim Al-Khalili's reply to my review of Johnjoe McFadden's book Quantum Evolution, by Matthew J. Donald"
- ↑ [8] "Quantum sectrets of photosynthesis revealed"
- ↑ [9] "Enzyme structure and dynamics affect hydrogen tunneling: The impact of a remote side chain (I553) in soybean lipoxygenase-1"
- ↑ Egan, G. (1999). Teranesia. Victor Gollancz Limited. ISBN 0-575-06854-X. http://gregegan.customer.netspace.net.au/TERANESIA/TERANESIA.html.
- ↑ Quantum Evolution: Outline page1
External links
 |
