More on the appendix

A little while back I reported about two papers by authors that stated that Darwin was wrong about the vermiform appendix, but that it does have a function. One of the authors, Bill Parker, recently emailed me a reply to my post and that of the commenters, and I deliver it here in full with permission:

We are careful to state that we have not actually
"directly demonstrated" the function of the appendix. However,
we have deduced what appears to be the function, and that
deduction is supported by a wide range of observations in
the fields of immunology, anatomy, medicine, and microbiology.

In fact, it is very difficult to imagine that the cecal
appendix is not a safe-house for bacteria. We know the
biofilms are the thickest there and the most secluded, and we
know the biofilms are protective, so we would need an
extraordinary explanation if we were to come to a different
conclusion. Sometimes a deduction is very strong. One of
your bloggers does not seem to appreciate that
"demonstration by deduction" is possible.

Nevertheless, we refer to "the apparent function" rather
than "the function" of the appendix when we are writing.

That being said, one of the main reasons we spent two years
working with evolutionary biologists at Arizona and
digging through the literature for that paper in the Journal
of Evolutionary Biology was to test the only "alternative"
to our deduction of the function of the appendix. As you
pointed out, that alternative was proposed by Darwin and
was still widely accepted, even in the scientific literature.

I noticed that one of your bloggers was hoping for a quick
and easy experiment to nail things down....
Unfortunately, we can't simply measure recovery from diarrhea
in people with and without an appendix for the answer. The
immune systems in people without an appendix are apparently
different than those in people without an appendix...as
indicated by the fact that one group got appendicitis and one
group did not. Perhaps more importantly, we don't know how
severe the diarrhea would have to be to necessitate the
apparent function of the appendix, and we have no idea if lab
animals would be suitable for a test, since we know they have
immune systems that are substantially modified by hygiene.

Parker also let me know that they have recently sent another paper on the cecal appendix and its function for review. Stay tuned.