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Re: [evol-psych] The human immune system may limit future evolution

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  • Steven D'Aprano
    ... This does not follow, since it ignores the fact that there isn t a fixed number of immune cells in the body, nor do all they all have to be produced at
    Message 1 of 2 , Jul 2, 2002
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      On Tue, 2 Jul 2002 16:18, Ian Pitchford quoted:

      > Dr George suggests that the limited number of functional genes in the
      > human genome may be a result of the presence of a more advanced
      > immune system. The immune system is designed to protect us from
      > disease, but it is important that the cells of the immune system do
      > not recognise our own tissues or cells, as this would lead autoimmune
      > disease.
      >
      > Autoimmune disease is avoided by killing off any immune cells that
      > recognise molecules produced by the body (self-molecules). This means
      > that the larger the genome, the more self-molecules the immune system
      > needs to tolerate.
      >
      > As a result, the immune system has to kill more immune cells. If
      > there are too many genes then this results in the vast majority of
      > immune cells dying, paralysing the immune system, and leaving the
      > body unable to fight off disease or infection.

      This does not follow, since it ignores the fact that there isn't a
      fixed number of immune cells in the body, nor do all they all have to
      be produced at once.

      Effectively the immune system can be considered (in part) a production
      line for producing a certain number of immune cells. Immune cells that
      recognise self-molecules are rejects, immune cells that don't are
      successes.

      While efficiency is important, you can still produce a healthy immune
      system with a 50% reject rate, or even 99% or higher. It will just take
      longer and be more wasteful. Since the immune system does not produce
      cells entirely at random, it isn't clear to me that a high failure rate
      would even be significantly more wasteful.

      There is a good test of Dr George's hypothesis. Are there any species
      with functioning immune systems with significantly more genes than we
      have?



      --
      Steven D'Aprano
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