In article <3mpu6i$emp at lastactionhero.rs.itd.umich.edu>, David Marshall <dmarshal at umich.edu> writes...
Selection is a *general* principle applicable
>to any level of biological organization .
> Natural selection can occur at all of these levels, but it is
>generally accepted that traits are most often explained by selection
>at the level of the "individual" organism (thus the phrase "selection
>is generally strongest at the level of the individual").
What you have said is OK, but please keep in mind that the original and
other subsequent posts were about "adaptation." Adaptation arises as
a result of the combined effects of selection and inheritance (genetics).
Adaptation is not the same as selection.
To the original poster: Don't confuse physiological adapation with
evolutionary adaptation. The physiological kind can happen at the level
of the individual. The evolutionary kind is not defined at the level of
the individual. It might be better to think of evolutionary adaptation
of a _trait_; individuals display traits, but evolution requires more
than one generation, and thus more than one individual.