From: colby@bu-bio.bu.edu (Chris Colby)
Newsgroups: talk.origins
Subject: "Jury-rigged" traits (was: Re: Vestigial organs)
Date: 21 Aug 92 22:29:52 GMT
Organization: animal -- coelomate -- deuterostome

In article <1992Aug20.123950.3651@desire.wright.edu> sbishop@desire.wright.edu writes:
>In article <22957@hacgate.SCG.HAC.COM>, root@lyra.scg.hac.com (Dave Fisher) writes:
>> I'm looking for a source of detailed information about "jury-rigged"
>> adaptations, vestigial organs, and the like.  I was considering reading
>> Darwin's book on Orchids... anyone have a better suggestion?

>> Dave Fisher

>Certainly *don't* miss _The Panda's Thumb_.

>Sue

Here are a few oft-cited examples of "jury-rigged" traits. Hope this
helps.

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	Many organisms show features of appallingly
bad design. This is because evolution via natural selection
cannot construct traits from scratch; new traits must be mod-
ifications of previously existing traits. This is called
historical constraint. A few examples of bad design imposed
by historical constraint:

	In parthenogenetic lizards of the genus _Cnenidophorus_,
only females exist. Fertility in these lizards is increased when
another lizard engages in pseudomale behaviour and attempts to
copulate with the first lizard. These lizards evolved from a sex-
ual species so this behaviour makes some sense. The hormones
for reproduction were likely originally stimulated by sexual
behaviour. Now, although they are parthenogenetic, simulated
sexual behaviour increases fertility. Fake sex in a partheno-
genetic species doesn't sound like good design to me.

	In African locust, the nerve cells that connect to
the wings originate in the abdomen, even though the wings are
in the thorax. This strange "wiring" is the result of the
abdomen nerves being co-opted for use in flight. A good
designer would not have flight nerves travel down the ventral
nerve cord past their target, then backtrack through the
organism to where they are needed. Using more materials than
necessary is not good design.

	In human males, the urethra passes right through the
prostate gland, a gland very prone to infection and subsequent
enlargement. This blocks the urethra and is a very common med-
ical problem in males. Putting a collapsible tube through an
organ that is very likely to expand and block flow in this
tube is not good design. Any moron with half a brain (or less)
could design male "plumbing" better.

	Perhaps one of the most famous examples of how evolution
does not produced designed, but "jury-rigged" traits is the
panda's thumb. If you count the digits on a panda's paw you will
count six. Five curl around and the "thumb" is an opposable digit.
The five fingers are made of the same bones our (humans and 
most other vertabrates) fingers are made of. The thumb is con-
structed by enlarging a few bones that form the wrist in other
species. The muscles that operate it are "rerouted" muscles
present in the hand of vertabrates (see S.J. Gould book "The
Panda's Thumb" for an engaging discussion of this case). Again,
this is not good design.

	In addition, organisms betray their history (phylogeny)
in their development (ontogeny). All mammals (including humans)
go through a stage were gills begin to form. Many organisms
contain useless structures, rudiments of traits or organs their
species contained in the past. The rudiments, or vestigal struct-
ures, are not evidence of good design, but of "jury-rigged" design.
Likewise, developmental patterns that form traits an organism
will never use are not evidence of good design. Both point to the
fact that present day organisms are the result of millions of
years of evolutionary tinkering, not creation via fiat of an
intelligent designer.