Evolution of the mind

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

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

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No problem here.

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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.

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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.

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

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. 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