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Thread: Life and the Evolution of Sex

  1. #1 Life and the Evolution of Sex 
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    Life is best understood as the replicator 'sliding down the hill of replication errors'. Every mutation that manages to crowd out the original or split off makes a drop downhill. Uphill we find the least-mutated life forms still alive today. Towards the bottom of the hill we find the most-mutated forms still alive today. (See diagram below)

    Nothing that happens downhill can serve as an explanation for anything uphill, because faulty replication is not a process that can look ahead in any way. Downhill, replication generally becomes more energy intensive and the replicator becomes more vulnerable to external disturbances due to the specialisation on specific energy sources. This vulnerability causes most life forms to die out as they slip further downhill.



    Sexual reproduction.
    A mutation to a replicator stumbles upon sexual reproduction. Now mutations that survive without fixating are allowed to build up among the sexually reproducing organisms. Sexual reproduction changes the single gene line into a gene pool of genetic diversity available to the replicator.

    The introduction of a genepool causes two important changes to life:
    1. A replicator building its organisms from a gene pool gets an extra lease of life because it gains a resistance against external disturbances. It can adapt within the gene pool without further mutations (like the peppered moth) keeping the replicator alive for longer. The genetic diversity within the genepool acts as a buffer against external disturbances allowing the replicator code to stay alive through genetic recombination.

    2. The sexually reproducing replicator becomes more vulnerable to mutations, causing increased complexity and speciation. A mutated gene can recombine in many more ways than before. This increases the chance of finding a combination that is capable of crowding out the original or splitting off, causing it to drop down the hill.

    But these two effects can not be the cause of sex appearing in evolution. They occur downhill from where sexual reproduction first occurs, after the build-up of a gene pool by further mutations.

    The cause of sexual reproduction is the increased energy efficiency offered by building in an error check in the replication process, allowing the mutated replicator code to crowd out its original. Sexual reproduction prevents the replicator from wasting energy on building faulty organisms that won't make it to replication (see blog). This lets the sexually replicating version achieve a higher growth rate on the available resources, crowding out the original.


    Cause and effect of sexual reproduction.
    This clear distinction between horizontal 'adaptation within the genepool' and vertical 'mutation downhill' can explain the cause and effects of sexual reproduction. The abundance of sexually reproducing life in today's world is due to the buffer a genepool provides against external disturbances and the increased vulnerability of the replicator to mutations that can take over or split off. Sexually reproducing life is caused by a mutation introducing an error check in replication which allowed it to crowd out the original.

    Present theories on evolution lead to confusion because they clump together adaptation within the genepool and mutation 'downhill' into a general mechanism called evolution. To understand the cause and effect of sexual reproduction, these two aspects of life need to be clearly separated, like the model of the 'hill of replication errors' does.

    Adaptation within the genepool is a largely reversible, almost directed process. Life is bound to find the 'best' genetic combination, given enough time for genetic recombination. Adaptation is about organisms within one species outperforming each other. Adaptation can occur without changing the potentially available code to the replicator. Adaptation can be seen as the replicator moving horizontally on the hill.

    Mutation downhill is a non-reversible, pure chance process. Due to its path dependent chaotic nature it is very hard to predict where it will go. Mutation is about permanent changes in the code available to the replicator, these are changes that affect the species in general. Mutations can open up long avenues of adaptation that life can take at great speed. This could give rise to 'sudden' large changes in a species phenotype. Mutations can be seen as the replicator slipping down the hill.

    Please have a look at my blog for a more complete explanation (work in progress) and the DIAGRAM if it doesn't show up correctly here.

    Adriaan


    Life sliding down the slope of replication errors.
    Adapting within the genepool. Mutating downhill.


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