Answers.Body: <p>Yes. The mutation can either disable or enable a gene.</p>
  
  <p>It's in the original NEAT implementation released by Dr. Kenneth O. Stanley.</p>
  
  <blockquote>
    <p>Declared in <code>genetics.h</code>:</p>
  
  <pre><code>void mutate_toggle_enable(int times); /* toggle genes on or off */
  void mutate_gene_reenable();  /* Find first disabled gene and enable it */
  </code></pre>
  </blockquote>
  
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Answers.Body: <p>Yes, the original gene is disabled, but is left in the genome. This can be seen on page 10, figure 3 of the paper linked (taken from the original paper <a href="http://nn.cs.utexas.edu/downloads/papers/stanley.ec02.pdf" rel="nofollow noreferrer">NEAT Paper</a>) where gene 3 is disabled, but not removed from the genome. This gene can be re-enabled by receiving the gene with the identical innovation number from a mating partner with the gene enabled during crossover.</p>
  
  <p>The original paper does not mention a mutation to re-enable genes, <a href="https://www.cs.ox.ac.uk/people/shimon.whiteson/pubs/ethembabaoglutr08.pdf" rel="nofollow noreferrer">but various other publications</a> and implementations after the original paper do. This is desirable for a number of reasons. Re-enable mutate allows for dropout to used in the implementation. It is also possible that certain genomes are disabling genes too quickly and this can help to correct for that.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
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Answers.Text: "This gene can be re-enabled by an enable mutate". I found no mention of this mutation. Source? NEAT paper says "Each mutation expands the size of the genome by adding gene(s)." Such 'enable' mutation would not add gene.
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Answers.Text: Sorry, I had forgotten this was not included in the original publication. Many other publications attempting to improve the NEAT method add this mutation type (See my edit).
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Body: <p>In the add node mutation, the connection between two chosen nodes (e.g. A and B) is first disabled and then a new node is created between A and B with their respective two connections. </p>
  
  <p>I guess that the former A-B connection can be re-enabled via crossover (is it right?). </p>
  
  <p>Can the former A-B connection also be re-enabled via mutation (e.g. "add connection")?</p>
  
Tags: <neural-networks><genetic-algorithms><neat><neuroevolution>
Title: Can mutation enable a disabled connection?
UserDisplayName: kuma
ThreadText: # Can mutation enable a disabled connection?
  
  (Asked by: username_0 on 2018-03-03)
  
  In the add node mutation, the connection between two chosen nodes (e.g. A and B) is first disabled and then a new node is created between A and B with their respective two connections.
  
  I guess that the former A-B connection can be re-enabled via crossover (is it right?).
  
  Can the former A-B connection also be re-enabled via mutation (e.g. "add connection")?
  
  **Tags:** neural-networks, genetic-algorithms, neat, neuroevolution
  
  ---
  
  ## 2 answers
  
  ### Answer by username_2 on 2018-03-03. Score: 3 | Accepted answer
  
  Yes, the original gene is disabled, but is left in the genome. This can be seen on page 10, figure 3 of the paper linked (taken from the original paper [NEAT Paper](http://nn.cs.utexas.edu/downloads/papers/stanley.ec02.pdf)) where gene 3 is disabled, but not removed from the genome. This gene can be re-enabled by receiving the gene with the identical innovation number from a mating partner with the gene enabled during crossover.
  
  The original paper does not mention a mutation to re-enable genes, [but various other publications](https://www.cs.ox.ac.uk/people/shimon.whiteson/pubs/ethembabaoglutr08.pdf) and implementations after the original paper do. This is desirable for a number of reasons. Re-enable mutate allows for dropout to used in the implementation. It is also possible that certain genomes are disabling genes too quickly and this can help to correct for that.
  
  > **Comments:**
  > **username_0**: "This gene can be re-enabled by an enable mutate". I found no mention of this mutation. Source? NEAT paper says "Each mutation expands the size of the genome by adding gene(s)." Such 'enable' mutation would not add gene.  
  > **username_2**: Sorry, I had forgotten this was not included in the original publication. Many other publications attempting to improve the NEAT method add this mutation type (See my edit).  
  
  ---
  
  ### Answer by username_1 on 2019-02-07. Score: 1
  
  Yes. The mutation can either disable or enable a gene.
  It's in the original NEAT implementation released by Dr. Kenneth O. Stanley.
  
  Declared in genetics.h:
  void mutate_toggle_enable(int times); /* toggle genes on or off */
  void mutate_gene_reenable();  /* Find first disabled gene and enable it */
  
  
  http://nn.cs.utexas.edu/soft-view.php?SoftID=4
  http://nn.cs.utexas.edu/?neat-c
  
  
  ---
  
  