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Re: Spandrel

Posted by Prof David West on Mar 14, 2021; 2:33pm
URL: http://friam.383.s1.nabble.com/Spandrel-tp7601069p7601081.html

Let me attempt to echo what i think I understand from your example and previous discussions where I lurked:

A mutation occurs in an organism resulting in an morphological change — i.e. a nose, modified jaw, and modified brain case.  I assume, first potential error, that this is a 'singular' change (e.g. a "face"), not three separate mutations and three different morphological changes to three different parts of the organism? [If there are three separate events, then how are they "coordinated?"]

One aspect of the original change, the nose, continues to change — is "decorated."

Second assumption (error): the same forces, mutation/selection, that cued the 'face' are prompting promulgation of new nose morphologies, the 'decorations'; which are selected among.

Core misunderstanding: it seems as if this demands some kind of "focused," on the nose, "micro-evolution." I do not see how such a weird phenomenon is not required; but cannot fathom from whence, and how, it came.

If mutation/selection occurs only at the 'whole', i.e. the face, then I do not see why any aspect of that face is "isolated" such that localized change is deemed somehow independent of global change and therefore merits the label: spandrel.

Now that you see how deep I am in a well of misunderstanding, is rescue possible or is it time to pour in the cement and cap the well?

davew


On Sat, Mar 13, 2021, at 9:21 PM, [hidden email] wrote:

Well, “elaboration of an epiphenomenon” was not the core of the mechanism I described.  It was a fancy little idea I added at the end.  So what about the mechanism that I described was difficulty to undertad.

 

n

 

Nick Thompson

[hidden email]

https://wordpress.clarku.edu/nthompson/

 

From: Friam <[hidden email]> On Behalf Of Prof David West
Sent: Saturday, March 13, 2021 8:41 PM
Subject: Re: [FRIAM] Spandrel

 

Nick,

 

first apologies for arrogance in first reply. I should have said that I find the definition derived from Bonner to be more understandable — to me — and, I think, it offers an actual mechanism / rationale that is absent, again to me, than "elaboration of epiphenomenon."  I am enjoying the essay and i see an interesting connection with Wegner's Arrival of the Fittest book. That means Jenny Q will have to read it because and I are working on a paper in that area.

 

davew

 

 

On Sat, Mar 13, 2021, at 5:37 PM, [hidden email] wrote:

> Bonner's a great guy, but I think he's wrong on that, or you're wrong 

> in interpreting him.  The whole thrust of Lewontin and Gould's work is 

> that there are developmental constraints in evolution.  Even according 

> to orthodox Darwinian theory, mutation is random, but only with respect 

> to the opportunities a mutation affords.  Nothing says that a mutation 

> can' be predictable, yet random in this sense.  Any "random" assertion 

> requires a point of view from which the stated variable is random.  Any 

> geneticist can tell you which mutations are more likely than others.  


> Nick 


> Nick Thompson

[hidden email]

https://wordpress.clarku.edu/nthompson/


> -----Original Message-----

> From: Friam <[hidden email]> On Behalf Of Prof David West

> Sent: Saturday, March 13, 2021 6:04 PM

> To: [hidden email]

> Subject: Re: [FRIAM] Spandrel


> Nick, thank you. I get the metaphor but I think my “definition” is more 

> correct than ‘elaboration of epiphenom’.   I get that notion from an 

> essay I am reading on randomness in evolution by John Tyler Bonner


> Davew


> On Sat, Mar 13, 2021, at 2:08 PM, [hidden email] wrote:

> > Hi Dave,

> > 

> > Ok, since you are also a metaphor enthusiast, let me explain a 

> > spandrel in terms of its root metaphor.  A spandrel, originally, is a 

> > decoration on the curved triangular spaces formed by the intersection 

> > of two perpendicularly intersecting archways.  The decorations are so 

> > suited to their settings that one might imagine that the hallways were 

> > designed to accommodate them, but, of course, it is they that are 

> > suited to fit the spaces affording by the intersecting hallways.  The 

> > same confusion exists with the human nose.  The nose is presumably 

> > what was left over when the brain expanded, and the gut and the jaw 

> > shrank.  It has been elaborated since to accommodate its new position, 

> > but the nose it self is the result of other adaptations, not of an 

> > adaptation FOR a nose.  The most graphic example, of course, of a 

> > spandrel is the erectal and colored pseudopenis (hypertrophied 

> > clitoris) born by the female stripped Hyena.  It is not an adaptation 

> > itself, but a consequence of powerful selection between female 

> > genealogies for feeding competition at the kill, which has select for 

> > high levels of testosterone in females.  (The females are heavier than 

> > the males, and, in general more nasty in every way

> > -- definitely examples of testosterone poisoning.)  The coloration of 

> > the pseudopenis is the spandrel-part, because selection has 

> > subsequently led to its "decoration".  Put another way, a spandrel is 

> > a phenomenon which is an elaboration of an epiphenomenon.

> > 

> > Does that help at all?

> > 

> > Nick     

> > 

> > Nick Thompson

> > [hidden email]

> > https://wordpress.clarku.edu/nthompson/

> > 

> > 

> > -----Original Message-----

> > From: Friam <[hidden email]> On Behalf Of Prof David West

> > Sent: Saturday, March 13, 2021 2:43 PM

> > To: [hidden email]

> > Subject: [FRIAM] Spandrel

> > 

> > A while back there was a lot of discussion of spandrels that I failed 

> > to grasp.

> > 

> > Is a spandrel a stable morphological trait that results from random 

> > chance rather than natural selection?

> > 

> > Or am I still ignorant.

> > 

> > Davew

> > 

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