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hominid mutation rates and the present environmental crisis

Posted by narguimbau on 09 Aug 2009 at 05:11 GMT

Please excuse my informality, perhaps understandable from my PLOS profile.

The findings in this article are perhaps to be expected in light of the greater-than-one genomic mutation rate in humans. See, e.g. "Estimate of the Mutation Rate per Nucleotide in Humans," Michael W. Nachman and Susan L. Crowell (Genetics, 2000). The combined findings strongly suggest that the hominids have reached a point at which a larger genome would be unsupportable.

I wrote an unpublished undergraduate mathematica biology paper at Harvard 40 years ago purporting to show (a) that if a species has a constant or average per-nucleotide mutation rate of R, then the maximum steady-state removal rate of deleterious mutations is exceeded when the number N of nucleotides exceeds 1/R, (b) that this ceiling is not substantially effected by redundancy or heterosexuality because the rapidity with which deletrious mutations can be removed is roughly inverse to the redundancy, (c) that based upon the information then available about per-nucleotide mutation rates, R and 1/N were of the same order of magnitude, and (d) accordingly, it was a reasonable conjecture that the more complex organisms had reached or were about to reach a maximum level of complexity as measured by the size of their genomes.

Those conjectures seem to be borne out by the present paper and Nachman/Crowell. There is a corollary - that at the time the biosphere reaches the point of maximum complexity, the most complex organisms and perhaps the system as whole also reach a maximum vulnerability to (a) collapse in the face of major perturations requiring rapid evolution, and (b) competition from non-DNA-based information storage and transmission systems.

Accordingly, it is reasonable to view the present crisis of the biosphere, in which rapid evolution of nonbiological information systems is occurring simulaneously with rapid collapse of biodiversity, the latter being unable to compete with the former, as not a fluke but as an inevitable stage in the evolution of a complex system in which random mutation is the vehicle for evolution of complexity.

I observe that at least in this layperson's mind, there was no obvious impediment to the evolution of high intelligence and technology millions of years ago, other than perhaps greater robustness and evolvability of simpler genomes, and that accordingly the roughly simultaseous occurrence on the planet of maximum DNA-based complexity and a competitor for DNA-based information storage and transmission is unlikely to be coincidental.

If the above conjecture is correct, the approach we take in attempting to stabilize the biosphere has to take it into account.

Nicholas Arguimbau

No competing interests declared.