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From: gallagher@husc4.harvard.edu (paul gallagher)
Newsgroups: sci.bio
Subject: Re: The Red Queen
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Date: Sat, 20-Dec-86 01:51:51 EST
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Posted: Sat Dec 20 01:51:51 1986
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In article <741@aecom.UUCP> werner@aecom.UUCP (Craig Werner) writes:
>	It has often been argued that biological change (evolution, I daresay)
>can occur even in the absence of environmental change.  To some this has
>been used to discredit the entire evolutionary scenario.  However, it
>was proposed (and I wish I know by whom) that interspecies competition may
>play a more important role than previously assumed. They dubbed this
>theory "The Red Queen Hypothesis", after the Red Queen's advice to Alice
>in "Through the Looking Glass":  
>	"Sometimes you have to run as fast as you possibly can just to 
>stay in the same place."

I think this refers to "character displacement".  When the ranges of two
similar species overlap, one may outcompete the other and cause its
elimination.  Alternatively, they can develop strategies to live together
in the same range.  One way is spatial segregation - one species lives in
one strictly localized habitat, the other lives in another so that they
avoid direct competition.   Another way is character displacement.  Either
one species comes to look very similar to the competing species, so that
selection acts upon all individuals as if they were just one species,
allowing the species to coexist, or the two species diverge in characters
so that the two species have slightly different habitats and thus again
can coexist.
For example, certain closely related agnostid trilobites seem to coexist
through size displacement.  It was predicted that size displacement would
have to be in the range of 1.28:1 in order to avoid competitive elimination.
The fossils in question were investigated and did indeed show ratios in
size of about 1.28:1.
Also, in the small area where the ranges of the trilobites Phacops iowensis
and Phacops rana overlap, P. iowensis diverged in morphology from P. rana,
while P. rana converged in some characters, diverged in others.
The source is Neil Eldredge, "Character displacement in evolutionary time"
American Zoologist 14 (1974), 1083-97.
However, Eldredge concludes that character displacement is not that important.


Another way a population might change without any change in its environment
is genetic drift.  Any very small population has only a limited, random 
sample of the genetic variability within a species, and whenever two
individuals reproduce,  some alleles will be lost, since only one chromosome
of each pair is passed down to the gametes.  Thus, in a small population,
there could be an evolutionary change in gene frequencies just through random
chance assortment.
Again, this process may not be very important.


Incidently, another way evolutionary change can occur far in excess of simple
responses to changes in the environment, is through changes in the timing
of development.
For example, neoteny: the occurence of sexual maturity in the juvenile animal.
It is believed that the early fish-like ancestors of vertebrates originated
when the free-swimming larvae of sea-squirts became able to reproduce, thus
eliminating the characters of the adult stage.
Similarly, the onset of maturity in the larvae of crustaceans may have given
rise to the small planktonic copepods.
Also, paedomorphosis: the retention of juvenile characters in the adult.
For example, in Cambrian trilobites the visual surface of the eye was surrounded
by an ocular suture - which caused the visual surface to be lossed during 
molting.  Probably through paedomorphosis, post-Cambrian trilobites abandoned
this system, replacing it with the juvenile form where the visual surface is
attached directly to the inner body.


In general, many people once thought that organisms were ideally adapted to
their environment.  So, in order to explain why they changed through time,
they had to say that their environment changed and that each change in a
characteristic corresponded to a perfection of its ability to function in
its environment.  Now, people realize that things are much more complex.
Stephen J. Gould uses a metaphor originated by Galton - the organism is not
a sphere which can be turned in any direction and any increment by changes
in the environment.  It is a polyhedron, each of whose faces is a point of
equilibrium.  Small environmental change will not turn the polyhedron to a
new face, and a big push which succeeds in changing the face of the polyhedron
may bring with it a whole set of changes not accounted for by natural
selection.
"Most of the changes in evolutionary viewpoint that I have advocated...fall
out of Galton's metaphor: punctuational change at all levels (the flip from
facet to facet, since homeostatic systems change by abrupt shifting to new
equilibria); essential non-adaptation, even in major parts of the phenotype
(change in an integrated organism often has effects that reverberate
throughout the system); channeling of direction by constraints of history
and developmental architecture.  Organisms are not billiard balls, struck
in deterministic fashion by the cue of natural selection, and rolling to
optimal position on life's table." - (Stephen J. Gould. "Is a new and
general theory of evolution emerging?" Paleobiology, 6(1), 1980, p. 129).


Paul G.