Re: [asa] Rejoinder 7C from Timaeus: Miscellaneous Short Replies

From: David Campbell <>
Date: Tue Oct 21 2008 - 18:23:44 EDT

> As for how long I should doubt evolution, well, I would say that I wouldn't insist on "full knowledge" of the evolution of literally everything, but I would like to see a few classic integrated complex organs or systems pretty well explained (say, 75% explained) in evolutionary terms: the eye, the flagellum, the avian lung, etc. If the Darwinian model could explain even one of these things with thoroughness, that would count greatly in its favour, and if it could explain half a dozen such things, then it is probable that it could explain everything else. But I'm waiting for even one nearly complete explanation from the realm of multicellular creatures.<

I'm always puzzled by why the eye gets invoked as a problem for
evolution. It's a terrible example of "irreducible complexity"
because it is highly reducible.

The simplest "eye" is merely having some sort of light-sensitive
chemical and a response to it. This is present in various protists
such as Euglena as well as in plants and animals. Such a rudimentary
light-sensing ability is useful-the organism can detect such things as
day versus night or hidden versus exposed or something moving past.
Concentrating the light-sensing ability in particular spots and
developing improved nervous systems both have practical advantages, so
there are plenty of intermediate steps, each advantageous.
Improvements to the eye, color vision, etc. are all nice add-ons that
would be favored by selection. In some cases, there are odd
combinations such as the cubomedusans with very good eyes but a very
simple nervous system and no real brain (apparently, they function to
help the animal avoid running into things in complex environments such
as mangrove forests; the volume of input overwhelms the animal and it
has to sleep if it gets a lot of input). As a rule, closely related
organisms with simpler eyes are known along with the forms with
complex eyes (e.g., jawless fish versus standard vertebrate, Nautilus
versus octopus and squid, ordinary polychaetes versus the pelagic
forms with good eyes, regular jellyfish versus cubomedusae). The step
in primates from red/green colorblind to normal human three primary
color vision is well-documented at the molecular level. The red and
green sensitive pigments are quite similar. A duplication and minor
mutation are all that was needed. A similar system evolved
independently in certain New World monkeys, but in this case the red
and green-sensitive pigments are alleles at a single sex-linked locus.
 As a result, males see green and blue or red and blue and are
red-green colorblind. Heterozygous females have three color vision,
and homozygous females are red-green colorblind. At the same time,
colorblind people survive just fine. Glasses help a lot, but plenty
of people have poor eyesight and survive.

Because we have the data for basal chordates, the evolution of the
vertebrate immune system (an example from Darwin's Black Box) is now
worked out in much detail (as was pointed out at Dover).

The avian lung is really a saurischian dinosaur lung-it was present in
various dinosaurs well before the origin of birds, so avian breathing
and flight are not an irreducible complex. It's a nice, efficient
system, but like the eye, the intermediate stages would seem to be
advantageous and so it fails the criteria for irreducibility.

Evolution by natural selection is statistical and situation-dependent,
but not tautological. There are multiple ways of achieving almost any
biological function, so the fact that more than one possibility can be
favored by evolution does not prove that it would favor anything. (It
is, however, true, that the mere fact that, e.g. a sociobiologist can
envision a scenario in which a particular human behavior could be
successful falls far short of proving that evolution is the full
explanation. Apart from issues such as whether that exact scenario
actually took place in human history, the more fundamental
philosophical problem of going from "here's a physical mechanism to
produce this behavior" to "how do we evaluate this behavior",
basically the is-ought problem, is neglected by those promoting
scientism). Of course, it is also inconsistent to claim that
evolution explains anything and to claim that it doesn't explain, e.g.
"irreducibly complex" things.

Lemski has some of the best data on evolution in action that is
available, but not the first or only by a long shot. There are myriad
examples of studies of evolution in action going back at least to the
peppered moth work, assuming you don't count accidental studies on
evolution such as the artificial selection throughout the history of
agriculture, and several other examples of raising bacteria or viruses
in the lab. Most evolutionary evidence, however, is evidence of past

Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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Received on Tue Oct 21 18:24:15 2008

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