There was a narrow interpretation of your sentence about where mutation occurs, to point out the trivial fact that mutation occurs at the gene. Perhaps if you had written about the level at which mutations have effect -- i.e., traits, which occur in individuals -- this could have been avoided ;-).
> "Heart attacks occur at the level of the individual." "No they
> don't, they occur at the level of the heart." "A heart which is in
> an individual." "But the individual is a member of a species, so
> therefore heart attacks occur at the level of the species!"
Right. So, this is the key thing: clearly selection occurs at the level of the individual because that is where traits (which are what are selected, not mutations or genes) manifest themselves. This, I continue to maintain, is current evolutionary theory 101. However, contrary to any impression I might have given, I believe that multi- level selection theory is correct. But, the explanation of it has to occur in terms of either:
(a) the features that appear at each level of selection that is proposed i.e., your point above. Faster gazelles outrun predators and survive to produce more off-spring, and ultimately increase the speed of gazelles as a species. This does not mean that selection occurred at the level of the species.
(b) or a feature that appears at an individual level does not benefit the individual but does benefit a higher level (kin, group, species, etc), inclusive fitness, etc.
--ravi