From: Brian Harper (harper.10@osu.edu)
Date: Tue Oct 14 2003 - 16:25:38 EDT
Here is a possible prediction to test two competing evolutionary theories.
IDers are more than welcome to make a prediction based on their theory. The
two competing theories are adaptationism and structuralism (for lack of a
better term, perhaps someone knows what name it really goes by). Well known
examples of the two are Richard Dawkins and Brian Goodwin respectively.
Suppose we identify some biological structure (morphology) of interest and
then identify the key geometrical parameters which describe that structure.
A great example of such a model is available on the web at
http://members.aol.com/macops/Raup.html . In this case we see shell
geometry defined in terms of the three parameters W, D, and T.
Now we need to visualize an n-dimensional theoretical morphospace where n
is the number of parameters (3 in the example above). This becomes rather
difficult with three parameters so, to illustrate, lets consider a case
with only two parameters, x and y. What I describe below is not limited to
two dimensional spaces.
A coordinate (specific x and y) in our hypothetical 2-dimensional (2D)
morphospace represents a specific possibility for the generic shape
considered. For example, if our generic shape is a rectangle then the
coordinate (2,3) would be a rectangle of base 2 and height 3. The space is
theoretical in the sense that no consideration is given, at this point, as
to whether the structures represented actually occur in nature.
Now for the first prediction. Find specific examples of the generic shape
in nature and plot these in the morphospace. The prediction of both
theories above is that the points will not be uniformly distributed across
the space. Instead, the points will be concentrated in one or more regions
of the space. The reason is: (a) (adaptationism) some structures are better
adapted than others and are thus favored by natural selection or
(b) (structuralism) developmental (or other physical) constraints make
some shapes impossible. (c) ID?
Now comes some really hard work. Using biomechanics (one of my interests)
assess the "performance" of the structure in relation to some function.
This must be done in terms of the morphospace parameters (x,y) so that the
performance (let's call it P(x,y)) can be plotted in the morphospace along
with the data above.
Now we have the second prediction. How will the contours of P(x,y) match up
with plotted points? Adaptationism predicts that the local concentrations
of observed shapes will be near the regions of local optimums in the
performance. Structuralism predicts that such a situation would be purely
coincidental and is not to be expected. ID?
The above is, of course, a more critical test of adaptationism than
structuralism. But the structuralist has the opportunity of doing something
similar, but even more difficult, than the above. They could develop a
model of the developmental (or other) constraint and show that the observed
shapes are predicted by that model. This has actually been done for the
case of spiral phyllotaxis (I've already discussed that in detail in this
group).
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