Re: [asa] Lab speciation

Hi Murray--

Work on the genetics of adaptation has grown and become more sophisticated lately, and there is much more to read than there was ten years ago. First, a few comments then I'll answer your questions (speaking only for myself).

One comment is that it is all too easy to hold to an oversimplified view of mutations. The fitness effects of mutations can and do vary, and it's simply not true that a non-advantageous mutation will be automatically removed from the gene pool. (Some very well-understood processes, including linkage and epistasis, can maintain mildly deleterious mutations in bacteria, and the possibilities are much more abundant in sexually reproducing organisms.) And the fitness of a particular mutation or trait is not a fixed parameter: today's hindrance can be tomorrow's breakthrough. Second, it is not true that all non-adaptive mutations are *strongly* deleterious, and many mutations are neutral or nearly so. Using terms like "harmful" and "beneficial" introduce strong biases that mask a much more complex reality.

Now your questions:
1. Your view of mutations seems to be simplistic. And recent findings (in bacteria) have led to a dramatic (1000-fold) upward adjustment of the adaptive ("beneficial") mutation rate. [Seehttp://www.sciencemag.org/cgi/content/abstract/317/5839/813 ] In other words, helpful mutations were never as rare as you seemed to believe, and now it seems we should consider them to be quite a bit more common than anyone supposed a year ago.

2. I would describe the findings as interesting but not overly remarkable. Certainly not mundane, but not earth-shaking. Why not overly remarkable? Because studies of adaptation, much more common now than in past decades, have shown that trajectories like the one described by Lenski's group are to be expected during adaptation. (I haven't seen the PNAS paper yet so I don't know the details.) Various forms of epistasis have been strongly implicated in the maintenance of sub-optimal alleles, and recent work has pointed very clearly to networks of "trade-offs" that have to occur during adaptation. See the work of Chris Hittinger and Sean Carroll, which I described recently on my blog.
[http://sfmatheson.blogspot.com/2007/12/gene-duplication-not-making-worse-what.html ]

Hope that helps, or even inspires,

Steve Matheson

>>> Murray Hogg <muzhogg@netspace.net.au> 06/04/08 4:59 PM >>>
Hi Burgy,

In the piece posted, it was the following that most interested me;

<snip>
   ... A few mutations occurred which actually were mildly
> harmful but did not outright kill the strain. Then a few more
> mutations occurred that combined with the previously harmful ones to
> provide a huge net positive benefit.
</snip>

One of the most obvious difficulties in biological evolution - as least
for a layman like myself - is that the formation of new information
within genomes (i.e. "mutations") seems almost always to be harmful. And
I add the "almost" as an exercise in charity - every mutation I'm
personally aware of is detrimental, usually fatal.

This point has always puzzled me as it really seems a block to
understanding the "how" of evolution. So this strikes me as a very
intriguing finding.

A few related questions, however;

(1) Are my remarks re "detrimental, usually fatal" effects of mutations
a fair assessment of the data - or an expression of ignorance of same?

(2) How does the finding in the snippet from your post (above) strike
practicing biologists? Is it remarkable or merely mundane?

(2a) If remarkable, is it so because it confirms what has been suspected
but not experimentally open to confirmation, or because it is actually
quite unexpected?

(2b) If mundane, am I right in thinking there must be OTHER confirmatory
examples of mutations which are in themselves harmful, but when taken in
conjunction with other mutations have provided a net benefit?

Thanks for a very informative piece and I look forward to any
constructive comment which might be forthcoming on questions (1) to (2b)
above.

Blessings,
Murray Hogg
Pastor, East Camberwell Baptist Church, Victoria, Australia
Post-Grad Student (MTh), Australian College of Theology

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Received on Wed Jun 4 23:25:09 2008