🚀 go-pugleaf

In article <20175@exodus.Eng.Sun.COM> silber@orfeo.Eng.Sun.COM (Eric Silber) writes:

> How is the evolution of 'atomic' instincts explained?
> By 'atomic' instinct, I mean a complex instinctual
> behaviour such as constructing a beehive.  The initial
> advantageous mutation must be how close to the fixed
> evolution-selected instinct?  Did the construction of 
> beehives start with a bee with a mutation that just
> caused it cough up a lump of wax?  An amorphous behavioural
> mutation too far from the finally selected stable instinct 
> seems unlikely to converge to the final instinct no matter
> how many generations pass.  It's clearly not magic or divine
> intervention that does it, but could there be some
> lamarckian channel that allows for accidentally performed
> proto-behaviours to be incorporated into the genome?????

Here are three possibilities.  All occur in nature, and none
requires the transmission of an acquired character.
 
1. Classical, _de novo_ adaptation -- A trait may be immediately 
   useful.  Example:  An organism undergoes a gene 
   duplication in an environment in which the extra gene product 
   happens to increase reproductive success.  As you point out, 
   a trait as complex as hive-building is unlikely to have arisen 
   in this fashion.

2. Preadaption -- A trait arises in response to one selection regime,
   but is "seized" by natural selection for another purpose.
   Example:  The tetrapod hearing apparatus arises as a modification
   of the vertebrate gill arches.  Your bee's ancestors may have
   had a half-dozen uses for coughed-up wax before it was used
   in hive-building.

3. Exaptation -- A trait that *isn't* adaptive is seized by selection
   for another purpose.  Example:  Over time, one of a pair of 
   duplicated genes acquires a new function owing to natural selection.  
   Duplicates of the cytoskeletal actin gene became the genes for 
   cardiac and striated muscle actins.  Your bee can cough up as 
   much utterly useless wax as she likes, so long as her reproductive 
   success (co-constituted with that of her queen, remember) is not 
   thereby decreased.
   
I think of George Williams as the person who first wrestled with
this question in a sophisticated way, although as Alan Rogers 
points out, the problem is much older.  E. Vrba and S. Gould 
more or less invented the idea of exaptation.


Ken Rice

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