RSS 2.0 Feed

» Welcome Guest Log In :: Register

    
  Topic: Co-option/change of function, Citations of this in the literature< Next Oldest | Next Newest >  
niiicholas



Posts: 319
Joined: May 2002

(Permalink) Posted: June 11 2002,01:03   

I was struck by this passage from Maynard Smith's The Theory of Evolution.  It almost sounds like it was written to respond to Behe, except that it was written in 1958 (I think; I have the 1993 Canto edition which is the fourth edition):

Discussing the origin of feathers, Maynard Smith writes  (pp. 303-304):

Quote

This example will help to explain one of the difficulties often encountered in explaining evolution in terms of natural selection.  It often seems that a perfected organ, although efficient at performing its function, is far too complex to have arisen by one or a few mutations, and yet is such that any intermediate stage between the absence of the organ and its full development would be incapable of performing this function. Thus it is inconceivable that the flight feathers of a bird could have arisen by a single mutation, but the intermediate stages between a scale and a feather would be useless for flight.  In this case the difficulty disappears once it is realized that during the early stages of the evolution of feathers, the latter were probably of selective advantage because they conserved heat, and only later did they become functional in flight.

This is a very common feature of evolution; a new structure evolves at first because it confers advantage by performing one function, but in time it reaches a threshold beyond which it can effectively perform a different function. We saw earlier that something of this kind occurred during the evolution of the elephant's trunk.  The flying membranes of bats and of pterodactyls were probably used in gliding before they were of any use in flapping flight, and, as Spurway has pointed out, small membranes along the sides of the body are found in some arboreal mammals which do not even glide, and these folds of skin render such animals more difficult to see by eliminating the shadows they would otherwise case.  Similarly, lungs were a selective advantage to fish living in stagnant waters, enabling them to breathe air, long before the descendants of these fish walked on land; in modern teleost fishes the lung has lost its function as a breathing organ, and has been transformed into a hydrostatic organ, the swim bladder.  These examples show that there is no reason to suppose that even the most complex structures underwent a long period of evolution and elaboration before they could function, and so confer selective advantage; rather their function may have changed once or even several times in the course of evolution.


(bold added)

This long-standing hypothesis regarding the origin of feathers has been strengthened by recent discoveries of fossil dinosaurs with non-flight feathers.  E.g. the fantastic pictures here:

http://research.amnh.org/vertpaleo/dinobird.html

E.g.:



Edited by niiicholas on June 11 2002,01:07

  
  7 replies since June 11 2002,00:44 < Next Oldest | Next Newest >  

    


Track this topic Email this topic Print this topic

[ Read the Board Rules ] | [Useful Links] | [Evolving Designs]