First, my comment was a bit too broad. It is only in Romans _5_
and I Tim. that this theme is important. Paul does not make use of it
in the rest of the letter. It is especially important to note that
nothing is said about Adam, or the _origin_ of sin, in 1:18-32 & 3:9-20,
where the general sinfulness of humanity is declared very strongly.
Belief in this common condition of sin does not depend on understanding
how it came about.
The argument that if Genesis 3 is not taken as literal history
then the need for salvation disappears is simply false. All of the
gospel writers speak, in different ways, of Christ as savior, but none
of them refer to an historical fall into sin as the problem from which
Christ saves us. & it can't be said that they took this idea for
granted, because it is not a significant theme of OT thought
(bracketing Gen.3 for the moment) at all.
The Hebrew _adham_ is, as is well known, a general term for
"human". A possible line of interpretation can understand the
statements about the creation & sin of Adam as referring to all human
beings. This does not exclude all concepts of a "first sin", for it
also applies to the first human beings.
Having said all this, I think that dealing with original sin,
its relation to death, &c in an evolutionary context is a significant
problem with which theologians have yet really come to grips, though
some attempts have been made. It only _can_ be treated adequately if we
take evolution seriously. No progress will be made if this problem is
simply used as an excuse for ignoring human evolution.