Quantum evolution (alternative)

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Quantum evolution is the hypothesis that genetic mutation can be adaptive, or directed through quantum effects.[1] It should not be confused with quantum evolution, a theory related to the modern evolutionary synthesis. The first publication on this subject, which appeared in a peer review journal, is by Vasily Ogryzko [2]. Biologist Johnjoe McFadden and the physicist Jim Al-Khalili subsequently published their own theory in 1999 [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]

Contents

[edit] 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 theory 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 in and of itself a controversial subject; as 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 explanation of the mechanism of adaptive mutation although most experimentalists would favour a process of random mutation accompanied by recombination and/or selection.

The 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 theory 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 (form proteins); otherwise, there would be no way for a comparison of the various outcomes of various mutations to occur, and thus no basis for the system to "decide" which mutations are more useful. Protein formation occurs at a rate of on the order of 10,000 times a second (10-5 seconds per protein formed).

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[4] (but see also McFadden and Al-Khalili's rebuttal [5]) 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 [6] and may even be responsible for the huge catalytic enhancement of reaction rates provided by enzymes [7].

If the theory of quantum evolution 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.

A different critique on quantum evolution can be made by asking why, if the cell can make use of quantum superpositions, it's not used for more purposes? Our immune system contains "general" agents that attack anything foreign and "specialised" ones (antibodies) that bind to specific proteins on specific bacteria. The latter must be made on demand. But why not use quantum superpositions to immediately attack the bacteria with every conceivable antibody at the same time and select the one that works? The answer is likely to be that more complex systems (than single protons in DNA or electrons and protons in enzymes) cannot be maintained in quantum coherent states for long enough to have biological significance.

Science fiction writer Greg Egan, in his book Teranesia, posed a similar yet more sweeping mechanism, whereby large sections of our observable universe are modeled as quantum superpositions of states, affecting not just biology, but the nature of space-time itself.

[edit] 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 what 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 [8], 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.

Of course, DNA, like all molecules, already obeys the laws of quantum mechanics, including quantum superpositions, collapses, and tunneling. The consequences of these laws are more commonly known as quantum chemistry, which explains all of the familiar chemical laws. Since the chemical behavior of DNA is reasonnably well-understood, and already includes both (ordinary) quantum mechanics and (ordinary) mutations, it is not yet clear where the additional effects of quantum evolution are supposed to arise. However, recent evidence indicating that the non-trivial aspects of quantum mechanics (e.g. tunelling, coherence, entanglement) may be required to account for even the most fundamental aspects of living systems (e.g. enzyme catalysis) indicates that quantum mechanics may indeed have a deeper role to play in biology than that currently appreciated.

[edit] References

  1. ^ a b c d McFadden, Johnjoe (2000). Quantum Evolution. HarperCollins. ISBN 0-00-255948-X; ISBN 0-00-655128-9
  2. ^ Ogryzko, V. V. (1997). A quantum-theoretical approach to the phenomenon of directed mutations in bacteria (hypothesis). [1] Biosystems 43, 83-95
  3. ^ McFadden J. J. and Al-Khalili, J. V. (1999). A quantum mechanical model of adaptive mutation. [2] Biosystems 50, 203-211
  4. ^ Donald, Mathew J. (2001). A Review of Quantum Evolution
  5. ^ [3] "Comment on Book Review of `Quantum Evolution' (Johnjoe McFadden) by Mathew J. Donald"
  6. ^ [4] "Quantum sectrets of photosynthesis revealed"
  7. ^ [5] "Enzyme structure and dynamics affect hydrogen tunneling: The impact of a remote side chain (I553) in soybean lipoxygenase-1"
  8. ^ Quantum Evolution: Outline page1

[edit] See also