Quantum Evolution, Johnjoe McFadden. Chapter 12

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Quantum Evolution - Chapter 12 - Quantum evolution

‘ … Quantum measurement influences the dynamics of quantum particles. The cell’s ability to perform quantum measurements on its coding protons will therefore influence their dynamics. But recall that proton dynamics inside DNA bases are involved in another vitally important biological phenomenon: mutation. If the target DNA base is replicated whilst the proton is attached to its normal nitrogen atom, then DNA polymerase will insert the complementary adenine and the daughter DNA molecule will encode exactly the same inactive enzyme as the parent: no mutation. If however, the DNA base is replicated whilst the proton is attached to the tautomeric (enol) nitrogen atom, then DNA polymerase will insert the incorrect base, guanine, in the daughter DNA strand and thereby generate a mutation. Yet, for the proton to be present at either position (rather than in a state of superposition), a quantum measurement needs to be made; and that measurement can only be performed under the appropriate environmental conditions (presence of lactose). Conditional quantum measurement thereby sits astride the engine of evolution: mutation.

The frequency of mutation of the target gene will clearly depend on the proton’s dynamics: how much time it spends at the tautomeric nitrogen. If this time is short then the mutation will be rare; if it is longer then the mutation will be more frequent. If a dense series of measurements were performed on the target proton at the tautomeric position then the quantum Zeno effect could freeze its dynamics at that position. But, as we have discovered, the cell is able to perform a dense series of measurements on the coding proton, if lactose is available. These measurements, in the presence of lactose, may enhance the probability of the proton remaining at the tautomeric position and thereby accelerate the rate of generation of a mutation.

Adaptive mutations

But environmental enhancement of mutation rates is precisely the phenomenon discovered by John Cairns when he discovered those enigmatic adaptive mutations that I described in Chapter 3. If you remember, adaptive mutations occur more frequently when they are beneficial to the cell, in direct contradiction of standard Neo-Darwinian evolutionary theory which states that mutations always occur randomly with respect to the direction of evolutionary change. The initial experiments performed by John Cairns, incubated E. coli cells that were unable to grow on lactose, on media containing lactose and on parallel media without lactose. If, as claimed by standard Neo-Darwinian evolutionary theory, mutations always occur randomly in relation to the direction of evolutionary change, then the same rate of mutation would be expected to be observed in both sets of cells. However, Cairns discovered that after a prolonged period of starvation, mutations that allowed the E. coli to utilise lactose increased in frequency. It appeared that the presence of lactose specifically enhanced mutations that allowed the cells to eat the lactose. The E. coli cell appeared to be able to direct its own mutations.

As I mentioned in Chapter 3, these experiments are still very controversial. Strict Neo-Darwinism is deeply ingrained in current biological thinking and most biologists are very reluctant to accept any revision of its dogmas. There is no question that the observations reported by Cairns are real; but many scientists maintain that there are likely to be more conventional explanations of Cairn’s experiments, than the existence of adaptive mutations. Nevertheless, others such as Professor Barry Hall at the University of Rochester have detected adaptive mutations in a variety of bacterial systems. In one of Hall’s most recent experiments he measured the mutation rates in non-growing E. coli cells for two different DNA bases in the same gene. When neither gene was beneficial then the mutations occurred at the same rate but when one of the genes conferred a selective advantage then its mutation rate was enhanced.

The problem with adaptive mutations is to provide a mechanism that could account for them. The interaction between the cell and its environment is conducted at the level of proteins, like beta galactosidase. The conventional information flow inside living cells is from DNA to RNA to protein. There is no conventional path by which information in the cell’s environment (the presence of lactose) can feedback to the DNA that encodes enzymes like beta galactosidase. The path: gene ® messenger RNA ® protein ® lactose is not reversible. Professor Hall commented in a recent paper that, … the selective generation of mutations by unknown means is a class of models that cannot, and should not, be rejected.

Quantum evolution may generate adaptive mutations by providing the required feedback loop: lactose ® protein ® messenger RNA ® gene, via conditional quantum measurement. The ability of the living cell to measure the positions of fundamental particles within the DNA double helix will be determined by the composition of its environment, in this case, the presence of lactose. Lactose arms the quantum measuring devices of the cell, enabling it to measure the position of the DNA protons that (potentially) encode the beta galactosidase enzyme. The cell may then perform a dense series of measurements on the position of DNA bases that will perturb the dynamics of those protons and hence enhance mutation rates. Quantum measurement may thereby enhance the rate of beneficial mutations to cause adaptive mutations and drive evolution.’