Andrew,
You mentioned something about complexity and sickle-cell anemia.
I don't mean to impose, but do you recall where you might have
heard this? I'm asking because that's twice in the space of about
a month that I've seen the HbS mutation which causes sickle-cell
anemia described as a "loss of complexity" or a "loss of information."
While this case is certainly not an "example of evolution" -- it's
an example of "selection", which may or may not result in evolution
-- I can't quite figure out what the change of a nucleotide base in
this case has to do with reducing complexity. Presumably a hemoglobin
protein of similar size is still expressed. I'm afraid that I'm at a
complete loss when it comes to "complexity calculus". How does one
run these calculations when a change-of-function mutation is maintained
by a selective environment?
Perhaps a better case for change in complexity could be made in the
cases of duplications or deletions along the genomes.
John Maynard Smith wrote a review article in Science (or Nature?) a few
years back discussing possible yardsticks for biological complexity.
In this work he mentioned that by nearly all accounts it appears that life
has increased in complexity over time. I do not believe he was ducking
the issue. For example, in his table, the bacteria/eukaryotic split
represented one obvious increase. Metazoans and plants also seemed to
represent signficant increases in complexity, however one might define
it. I'm not sure if there was a big difference that could be defined
between, say, insects and amphibians, however. If we go by total genomic
length, plants win hands down, but it we go by estimated numbers of genes,
metazoans do best. However, I don't recall that there is any good metric
to argue for vast differences in complexity among fish, amphibians,
reptiles, birds and mammals. Humans, as to be expected, were somewhere
around average in this lineup.
Regards,
Tim Ikeda tikeda@sprintmail.com (formerly timi@berkeley.edu)
PS - I'm trying to sneak by, sending this letter to the listserver
while not being subscribed. Heck, maybe this can work...