Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 79 (8897 total)
Current session began: 
Page Loaded: 03-20-2019 11:47 AM
207 online now:
dwise1, JonF, kjsimons, PurpleYouko, Tangle, Tanypteryx (6 members, 201 visitors)
Chatting now:  Chat room empty
Newest Member: WookieeB
Post Volume:
Total: 848,484 Year: 3,521/19,786 Month: 516/1,087 Week: 106/212 Day: 22/14 Hour: 2/0


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Evolution of the mind
kalimero
Member (Idle past 519 days)
Posts: 251
From: Israel
Joined: 04-08-2006


Message 1 of 11 (304928)
04-18-2006 9:32 AM


This is the article:
http://faculty.ed.uiuc.edu/g-cziko/wm/05.html

Please read at least 'The Development of the Brain' section.

We thus see that the normal development of the brain depends on a critical interaction between genetic inheritance and environmental experience. The genome provides the general structure of the central nervous system, and nervous system activity and sensory stimulation provide the means by which the system is fine-tuned and made operational. But this fine-tuning does not depend on adding new components and connections in the way that a radio is assembled in a factory, but rather it is achieved by eliminating much of what was originally present. It is as if the radio arrived on the assembly line with twice as many electrical components and connections as necessary to work. If such an overconnected radio were plugged in and turned on, nothing but silence, static, or a hum would be heard from its speaker. However, careful removal of unnecessary components and judicious snipping of redundant wires would leave just those components and connections that result in a functioning radio. This snipping is analogous to the elimination of synapses in the human brain as part of its normal development.

My question is whether we can say that the neurons are going thruogh evolution (obviously natural selection), and if so can we use the concepts we have encountered in biological evolution of alleles (gene flow, macroevolution, gene migration, exc') to predict what those mean in terms of neuronal evolution, and what their affects are?


Replies to this message:
 Message 3 by EZscience, posted 04-19-2006 11:09 PM kalimero has not yet responded

    
AdminPD
Inactive Administrator


Message 2 of 11 (305366)
04-19-2006 8:52 PM


Thread moved here from the Proposed New Topics forum.
  
EZscience
Member (Idle past 3228 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 3 of 11 (305388)
04-19-2006 11:09 PM
Reply to: Message 1 by kalimero
04-18-2006 9:32 AM


Emphatically NO
What is discussed here is a DEVELOPMENTAL process, not an EVOLUTIONARY process, i.e. it happens within the lifetime of an individual.

Evolution is a property of populations and species - not individuals.
It happens across generations - not within them.

And this is not to say that evolution did not generate the apparent excessive innervation in the developing brain, only that the process of neural attrition is a developmental one.

Apparently, it is advantageous to have a lot of excess nerve cell assemblies in the brain initally in order to facilitate development of the multiple pathways that will prove ultimately most successful for the brain's final functionality. This would make sense if the most effective pathways for the adult organism were unidentifiable in early stages of development, but required multiple templates in order to be established later in development.

It suggests, to my mind, an adaptation of neural physiology to unpredictable determinants of 'neural fitness' within the lifetime of individuals - the 'best ' pathways are not predictable in advance so multiple ones are (initially) established in order to provide alternative working systems, only a few of which will be retained during later stages of development, as determined by their usefulness to the individual.

This is not evolution - it is phenotypic flexibility.

This message has been edited by EZscience, 04-19-2006 10:16 PM


This message is a reply to:
 Message 1 by kalimero, posted 04-18-2006 9:32 AM kalimero has not yet responded

Replies to this message:
 Message 4 by nwr, posted 04-19-2006 11:30 PM EZscience has responded

  
nwr
Member
Posts: 5585
From: Geneva, Illinois
Joined: 08-08-2005


Message 4 of 11 (305390)
04-19-2006 11:30 PM
Reply to: Message 3 by EZscience
04-19-2006 11:09 PM


Re: Emphatically NO
What is discussed here is a DEVELOPMENTAL process, not an EVOLUTIONARY process, i.e. it happens within the lifetime of an individual.

I agree with this. However, the OP is looking at something like Gerald Edelman's theory of consciousness, which Edelman refers to as neural Darwinism. See, also, the Wikipedia entry.

Evolution is a property of populations and species - not individuals.

Neural Darwinism looks at the brain as a population of neurons.

Personally, I'm skeptical of neural Darwinism as an account of human consciousness. But it is out there as a theory, and it is my impression that it is what the OP is wanting to discuss.


This message is a reply to:
 Message 3 by EZscience, posted 04-19-2006 11:09 PM EZscience has responded

Replies to this message:
 Message 5 by EZscience, posted 04-20-2006 7:43 AM nwr has not yet responded

  
EZscience
Member (Idle past 3228 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 5 of 11 (305420)
04-20-2006 7:43 AM
Reply to: Message 4 by nwr
04-19-2006 11:30 PM


Two usages
quote:
In one usage it is the theory that consciousness can be explained by Darwinian selection and evolution of neural states.

No problem here.

quote:
In the other it describes a process in neurodevelopment where synapses which are being most used are kept while least used connections are destroyed or 'pruned' to form neural pathways.

This process might seem superficially analogous to natural selection, but I don't think it is a useful analogy, nor do the similarities go very deep. Natural selection works via mortality on individuals to change the genetic makeup of a population over generations - the nerve cells are not being selectively eliminated here - only their excess connections - nor is there is any further reproduction in their population (normally), although some new connections can be formed later in development. I understand that this process of pathway consolidation does involve changes in neuronal RNA, but the selective force is a positive one in this case - 'usage' of a particular pathway 'selects' for consolidation of synapses, and degradation of un-used synapses occurs through lack of use. However, I have difficulty viewing synapses as 'units of selection' analogous to individual organisms because they do not exist as independent entities but are merely connection points between cells. It takes at least two cells to make a synapse.
As far as this process might be considered selective, the system's function as a whole is, in a sense, exerting a form of selection intrinsically on itself. The brain is essentially a closed system. Not very analogous to NS on either level here, in my view. I think this is more constructively viewed as a process of developmental canalization at the neural level, sensu Wigglesworth.


This message is a reply to:
 Message 4 by nwr, posted 04-19-2006 11:30 PM nwr has not yet responded

Replies to this message:
 Message 6 by kalimero, posted 04-20-2006 6:08 PM EZscience has responded

  
kalimero
Member (Idle past 519 days)
Posts: 251
From: Israel
Joined: 04-08-2006


Message 6 of 11 (305522)
04-20-2006 6:08 PM
Reply to: Message 5 by EZscience
04-20-2006 7:43 AM


I think that maybe I wasnt so clear about what I meant by evolution here, though nwr was very close (Its my first topic :) ). When I started the topic I was thinking of Richard Dawkin's idea of natural selection of ideas - he calls the units of those basic ideas meames (I'm not sure if I'v writtin it correctly, I read it in hebrew) as a very real equivalent of alleles; although these meames arent chemicals like DNA or RNA, they still seem (nothing proven yet :) ) to 'behave' according to the basic laws of evolution. My notion of evolutionary prosseses is not limited to genetics, not even biology - as it has been demonsrated in this forum many times (with evolving software, ext') - so when I look at neuronal development, though I understand that it is a developmental prosses, I can recognise the charactaristics (critiria you may say) of evolution (correct me if I'm wrong :) ) :
1. reproduction - neurons grow throuout life, although less in older age, there are always enough neurons to go through selection.
2. modification - not much to say, neurons are different from each other.
3. selection - I thimk that the genetic evolution of the brain was "pushed" to form a brain with the capability to 'freely' respond to "pressures" from the outside world (that are relevent to the senses - obviously). I think thats why people tend to describe the brain as flexible.
4. heredity - Like nrw said :
Neural Darwinism looks at the brain as a population of neurons.

Though this may be a closed system, the way thay "pass along" their ability to do somthing well is two-fold:
(a) The genes that evolved to produce a brain capable os responding well to the outside world are passed on through biological reproduction. Though these capabilities are only the potential for a functionality of the brain (in higher brian functions only).
(b) The ideas themselves are "reproduced" from person to person and give that person and an advantage over others (language, understanding of the physical world, the ability to make pizza, and many more) and with them so are the neurons reproduced (I think it works that way).
SO....while genes reproduce verticaly, meames (or ideas or neurons) seem (tentatively) to reproduce both horizontaly and verticaly. Horizontal reproduction meaning the sharing of ideas between people and vertical meaning cultural/religious heritage.

* Side note: ever since I started writing in this forum I find myself being more and more cautious with my use of words that might seem ambiguous. :laugh:


This message is a reply to:
 Message 5 by EZscience, posted 04-20-2006 7:43 AM EZscience has responded

Replies to this message:
 Message 8 by EZscience, posted 04-21-2006 8:52 AM kalimero has responded

    
kalimero
Member (Idle past 519 days)
Posts: 251
From: Israel
Joined: 04-08-2006


Message 7 of 11 (305543)
04-20-2006 7:58 PM


the title
The title of this topic was more relevent than I intended. Here is a definition of "mind" (notice no. 2):
http://www.m-w.com/dictionary/mind
    
EZscience
Member (Idle past 3228 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 8 of 11 (305638)
04-21-2006 8:52 AM
Reply to: Message 6 by kalimero
04-20-2006 6:08 PM


Kalimero writes:

I can recognise the charactaristics (critiria you may say) of evolution

I'm still having troupble seeing these.

I can see some parallels, but there are still some important differences that, to me, are enough to negate the usefulness of the concept of 'evolution driven by natural selection' as an analogy for brain development.

Kalimero writes:

1. reproduction - neurons grow throuout life, although less in older age, there are always enough neurons to go through selection.

Growth is not reproduction. They can sometimes regenerate after injury, but neurons in the CNS cannot replicate themselves or give birth to progeny.

Kalimero writes:

modification - not much to say, neurons are different from each other.

That's variation in your 'population'. One criteria for evolution, yes, but 'descent with modification' is now broadly interpreted to mean heritable mutation. And there can be no heritability without reproduction.

Kalimero writes:

selection - I thimk that the genetic evolution of the brain was "pushed" to form a brain with the capability to 'freely' respond to "pressures" from the outside world (that are relevent to the senses - obviously). I think thats why people tend to describe the brain as flexible.

If you want to postulate a selective force, I think we will need to define it more precisely than that. As I understand it, the 'selective force' supposedly at work here is 'usage' - synapses that fire frequently make for neural pathways that are more likely to fire again in the future. Once agian, I have a problem with a 'synapse' as a unit of selection, though.

Kalimero writes:

heredity

I am still not clear on what kind of mechanism in the brain could possibly be analogous to heredity, simply because I have yet to find any form of neuronal reproduction that would seemingly be a prerequisite for heredity.

This message has been edited by EZscience, 04-21-2006 07:53 AM


This message is a reply to:
 Message 6 by kalimero, posted 04-20-2006 6:08 PM kalimero has responded

Replies to this message:
 Message 9 by kalimero, posted 04-21-2006 12:27 PM EZscience has responded

  
kalimero
Member (Idle past 519 days)
Posts: 251
From: Israel
Joined: 04-08-2006


Message 9 of 11 (305678)
04-21-2006 12:27 PM
Reply to: Message 8 by EZscience
04-21-2006 8:52 AM


I can see some parallels, but there are still some important differences that, to me, are enough to negate the usefulness of the concept of 'evolution driven by natural selection' as an analogy for brain development.

It isnt an analogy but litiraly evolution, just not the common biological (genetic based) evolution we are use to. The basic component that is passed on and modified here is the idea.
I think now that the wiring of neurons in the more basic regons of the brain - the visual reigon for example - may not have these advanced evolutionary 'tactics' but relies mostly on an inherant genetic tendancy towards seeing more than selection and modification, though the selectionary prosses still exists.
Growth is not reproduction. They can sometimes regenerate after injury, but neurons in the CNS cannot replicate themselves or give birth to progeny.

The growth I meant was the ability of the brain to rewire itself as to give a fuctionality to almost any reigon in the brain - after lossing sight or something. The neurons themselves dont do the actual reproduction in terms of evoltion (your right about that), the units that do that are the ideas - they reproduce and are modified.
That's variation in your 'population'.

I agree, good call. :) But these are neurons that "store" ideas (I realy need a better word for that).
One criteria for evolution, yes, but 'descent with modification' is now broadly interpreted to mean heritable mutation.

And there can be no heritability without reproduction.

See the above comment about ideas reproducing.
Once agian, I have a problem with a 'synapse' as a unit of selection, though.

I understand that this process of pathway consolidation does involve changes in neuronal RNA, but the selective force is a positive one in this case - 'usage' of a particular pathway 'selects' for consolidation of synapses, and degradation of un-used synapses occurs through lack of use. However, I have difficulty viewing synapses as 'units of selection' analogous to individual organisms because they do not exist as independent entities but are merely connection points between cells. It takes at least two cells to make a synapse.

Its not the synaps itself that makes for a unit of selection, but the 'information' or ideas it stores. This is analogous to DNA or RNA (not ribozymes) as a random selection of nuleotides - but put them in the right order and they 'contain information' {its not a very good analogy :) ).
I am still not clear on what kind of mechanism in the brain could possibly be analogous to heredity, simply because I have yet to find any form of neuronal reproduction that would seemingly be a prerequisite for heredity.

The neurons that contain ideas and pass them on to other poeple or are modified through interation with the world or with other 'ideas', this is analogous to heredity.
This message is a reply to:
 Message 8 by EZscience, posted 04-21-2006 8:52 AM EZscience has responded

Replies to this message:
 Message 10 by EZscience, posted 04-21-2006 12:50 PM kalimero has responded

    
EZscience
Member (Idle past 3228 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 10 of 11 (305683)
04-21-2006 12:50 PM
Reply to: Message 9 by kalimero
04-21-2006 12:27 PM


The 'idea' as a unit of selection
It's getting a little clearer now.

Reproduction of ideas? Yes, but are we considering replication 'between' individuals, or just within a single brain? Two differetn models would be needed.

Heredity of ideas? Definitely - although between organisms this would be considered 'cultural evolution'. There is some evidence of heredity of memory within neurons via changes in their RNA.

Ever here of this flatworm experiment? Not very conclusive and they've had problems with replication, but I think we have to be open to the idea that there may be some chemical basis for heritability of memory.

Selection? I guess we need a mechanism here that would work within the brain for determining which ideas were 'best' to keep.

Kalimero writes:

Its not the synaps itself that makes for a unit of selection, but the 'information' or ideas it stores.

The problem here is that the synapse doesn't really 'store' any information - it is merely a connection between two nerve cells. So changes in the 'resistance' of a synapse to fire are mediated by both neurons, the upstream one and the downstream one (by my understanding).

I am going to have to give this some more thought when I have time.

EZ


This message is a reply to:
 Message 9 by kalimero, posted 04-21-2006 12:27 PM kalimero has responded

Replies to this message:
 Message 11 by kalimero, posted 04-22-2006 6:43 AM EZscience has not yet responded

  
kalimero
Member (Idle past 519 days)
Posts: 251
From: Israel
Joined: 04-08-2006


Message 11 of 11 (305868)
04-22-2006 6:43 AM
Reply to: Message 10 by EZscience
04-21-2006 12:50 PM


Re: The 'idea' as a unit of selection
Reproduction of ideas? Yes, but are we considering replication 'between' individuals, or just within a single brain? Two differetn models would be needed.

I agree. There must be a differnce between the two, but replication occurs between individuals. Selection occurs both inside the brain - choosing ideas that fit the individuals sensory perseption of the world - and between brains - ideas 'look for' ideas of the same kind (that agree with them), the latter can be an analogy to sexual selection.
Heredity of ideas? Definitely - although between organisms this would be considered 'cultural evolution'.

OK, so where does this kind of evolution stem from (physiologicaly)?
Can we see the other types of evolutionary processes in this type of evolution (genetic drift ext')?
Ever here of this flatworm experiment? Not very conclusive and they've had problems with replication, but I think we have to be open to the idea that there may be some chemical basis for heritability of memory.

How exactly does the flat worm (Dugesia - very cute :) ) aquire the RNA sequence after degrading it?
The problem here is that the synapse doesn't really 'store' any information - it is merely a connection between two nerve cells. So changes in the 'resistance' of a synapse to fire are mediated by both neurons, the upstream one and the downstream one (by my understanding).

Not one synaps but many of them - equated to a code (just like DNA).
Though I dont realy know alot about this.
This message is a reply to:
 Message 10 by EZscience, posted 04-21-2006 12:50 PM EZscience has not yet responded

    
Newer Topic | Older Topic
Jump to:


Copyright 2001-2018 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2019