CR and rate of maturation

Aubrey de Grey ag24 at mole.bio.cam.ac.uk
Fri Oct 2 10:10:44 EST 1998


James wrote:

> I don't understand all this conjecture (fact?) that mice in the lab are
> bred for early reproduction (at least any more so than in the wild).
> Obviously I can see why some strain that has been reproducing for a
> long time at Jackson labs could be construed to have been selected in
> such a manner since more prolific mothers and mothers that breed at an
> earlier age might have a tendency to take over the population (but then
> again, they might not, it depends on how they have their breeding
> scheme set up).  But that is the case in the wild as well.

Yes; one difference is that in the lab there is almost no selection for
anything else (hardiness to cold reaction speed to avoid predators; one
could go on almost forever), and that may allow the selection for rapid
reproduction to proceed further than in the wild.  Also, the selection
for early reproduction may be intensified by the absence of seasons in
the lab -- the fact that lab mice can get through far more generations
(twice as many?) than wild mice.  (I don't say that this is a conclusive
argument, by any means; just that it seems hard to rebut conclusively.)

> And, once outside of a "commercial" environment I wouldn't think that
> the selection even exists.  In the types of mouse experiments that I am
> familiar with it wouldn't make any difference since when they breed all
> progeny are kept, and the parents are simply separated when they don't
> want any more mice.  Of course, you could argue that the damage has
> already been done by enduring a long period of time where this type of
> selection might have been the case, and that not much drift is going to
> occur to fix the problem in the few generations typical of most
> experiments. I'll buy that 100%, but that doesn't address the first
> issue.

That's exactly what I'm suggesting, yes: that the decades of maintenance
in stock may have done damage that's essentially irreversible by only a
few years of selection.  I would really like to know the details of how
(and from what starting material) Walford et al selected their strains --
it may make all the difference.

Aubrey de Grey




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