[Taxacom] Pre-Adaptation and Function(al) Shift

[Robin Leech]

Hi One and All,

Several of you, after I sent an electronic copy of the paper that I 
and Al Cady wrote and published in 1994, titled, Function Shift and 
the Origin of Insect Flight [Australian Biologist Vol. 7(4): 160-168], 
had questions about the terms "Pre-adaptation" and "Function(al) Shift".

With that in mind, I am defining these terms as we meant them in 
the article.

Pre-adaptation: a major change in function of an organ with little or 
    no change in structure.  That is, an organ is suited for a new function 
    before function arises.
    Our legs had the function of walking, running, and with the help of 
    arms, climbing trees and cliffs.  
    A pre-adaptation would be the use of arms and legs for swimming, 
    which is a completely new function.  No change is needed for the 
    arms and legs, but the organism has to learn to use them for 
    swimming. This leads directly to a function(al) shift.  The main problem 
    at this point is that the organism has to learn to use the organ for 
    a completely new function, and the expression "sink or swim" seems 
    rather a propos here

Function(al) Shift: is the acquisition and retention of a new function, 
    or several new functions, by an existing organ which previously had 
    one or more other functions. At this point in history, there has not been 
    a change in structure of the organ. 
    I believe that the example of gills becoming wings is the best example 
    to discuss.
    Vis-a-vis our paper, gills became wings. The early wings were 
    identical to gills, and with fossils, especially those 250 million years 
    old or older, it would be impossible to distinguish a fossil gill from a 
    fossil wing, particulary during the transition period.
    Once the shift from gills to wings was made, wings literally took off 
    and had lives of their own, then fossil wings were distinguishable from
    fossil gills.  
    Among other things, fossil wings served for: epigamic display, 
    pheromone dispersal, flying, thermoreulation, protection, camouflage, 
    sound producers, and gas exchange.

We hope this clarifies these questions.  Please do not hesitate to contact 
us if you have questions.

Robin Leech
(for Leech and Al Cady)