I don't see what's artificial about it. The concentration of free radicals
in the cell, for instance, is partly a matter of what kinds of foods are
eaten. At least that's my understanding. Fresh fruits and vegetables are
supposed to fight cancer. Cancer is caused by somatic mutations. Ergo,
diet can significantly affect mutation rate.
And why are replication errors considered the "normal" way mutation occurs?
How do you determine whether a mutation was caused by a replication error
or a mutagen?
Also, in Drosophila 50-85% of the mutations are caused by transposon
insertions , which I assume occur at other times than during cell
division. (Of course transposons preferentially target non-coding DNA,
so you might not want to count them in a discussion of the mutation rate
 "Cytosine methylation and the ecology of intragenomic parasites", by
Jeffrey Yoder et al, Trends in Genetics, Aug 1997, vol 13, no. 8. They
also say that the fraction of mutations due to transposons varies wildly
with the species; in humans, it's only 1 in 500.
Rich Daniel firstname.lastname@example.org http://www.dnaco.net/~rwdaniel/