December 1, 2009
James J. Bull
The University of Texas at Austin
Section of Integrative Biology, College of Natural Sciences
1 University Station C0930
Austin, TX 78712
Dear Dr. Bull:
A brief note in NATURE comments on an article on mutation rate in a bacteriophage virus: Genetics dol:10.1534/genetics.109.108803(2009). Their opening sentence starts, “High mutation rates are thought to drive populations to extinction ...” That certainly caught my eye. It is something I have been thinking for some years and continue to think, with a reservation I shall mention soon. To see it proposed as common wisdom comes as a surprise, since I find little interest in the subject.
But it has to be true. Evolution has been around a long time. Evolution is capable of increasing complexity by – crudely speaking – increasing the amount of genetic information an organism carries. That has to increase the deleterious mutation rate, and there must be a limit. It seems to me to be reasonable to assume that higher organisms are working against their maximum possible mutation rate. This of course would account for punctuated equilibrium in evolution; evolution stalls until some lucky break makes it possible to abandon some genetic material and thus exploit new possibilities.
For instance an invasive species, having left behind natural checks on its growth, may overgrow native species and, I would expect, evolve to be more aggressive still in this new environment until balance is achieved by the evolution of something to take advantage of the newcomer’s presence. Maybe we shall have a kudzu beetle some day.
Similarly you have demonstrated that your viruses after having been exposed to a higher mutation rate may be fitter in the lab but might not be so fit in the wild because they dropped adaptations they did not need in the more sheltered environment.
The problem is that, unlike viruses, higher animals generally are obliged to have sex in order to reproduce. And the reproductive rate is strongly affected by the mating pool size. The enclosed DVD gives much evidence for this and also mentions my own computer program that builds a virtual population using standard Mendelian laws and demonstrates the same pattern of growth rate compared with population size seen in the real world.
As I said, this concept – NATURE’s remark notwithstanding – has not gained a lot of attention. I think it should. The DVD points out how important it is. If you or anyone you know of would take an interest in working out the details, do let me know.
The program models genes tuned to each other. That may be what is going on. But there is another possibility. It is possible to create an embryo by injecting a sperm into an egg when the sperm could not have successfully entered on its own. Thus there may be a safety check. The egg will not begin to make an embryo if the sperm does not match its own DNA closely enough. It may be the safety check rather than the actual genetic mismatch that my program is modeling. This is one of the things that need more skill applied than I can bring to bear.
Sincerely,
M. Linton Herbert
SilentNursery.com
To be posted as an open letter on nobabies.net
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