Answers.Body: <blockquote>
    <p>When do mutations occur and between which nodes?</p>
  </blockquote>
  
  <p>There are two types of mutations in the <em>NEAT</em> model, each of them appears randomly during one epoch on different individuals; the number of structures affected by mutations may vary depending upon the nature of the problem.</p>
  
  <ul>
  <li>A new gene/node is added to the structure and properly linked.</li>
  <li>A new connection between two nodes is added.</li>
  </ul>
  
  <blockquote>
    <p>When mating, what happens if 2 genes have the same connection but a different innovation number?</p>
  </blockquote>
  
  <p>During a single epoch/generation every mutation is tracked and if the same mutation appears it can't have the same global <em>innovation</em> number. <em>Same mutation, same innovation number.</em> In that way, during the mating phase, there is no decisional problem which leads to prefer one structure to the other.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2017-01-13T15:28:25.397Z
Answers.LastActivityDate: 2019-07-07T18:57:44.867Z
Answers.LastEditDate: 2019-07-07T18:57:44.867Z
Answers.UserDisplayName: Lovecraft
Body: <p>I have read the <a href="http://nn.cs.utexas.edu/downloads/papers/stanley.ec02.pdf" rel="nofollow noreferrer">Evolving Neural Networks through Augmenting Topologies (NEAT)</a> paper, but some doubts are still bugging me, so I have two questions.</p>
  
  <ol>
  <li><p>When do mutations occur? Between which nodes?</p></li>
  <li><p>When mating, what happens if 2 genes have the same connection but a different innovation number? As far as I know, mutations occur randomly and thus it is possible that 2 genomes have the same mutation.</p></li>
  </ol>
  
Tags: <neural-networks><genetic-algorithms><evolutionary-algorithms><neat><neuroevolution>
Title: What happens if 2 genes have the same connection but a different innovation number?
UserDisplayName: Miemels
ThreadText: # What happens if 2 genes have the same connection but a different innovation number?
  
  (Asked by: username_0 on 2017-01-11)
  
  I have read the [Evolving Neural Networks through Augmenting Topologies (NEAT)](http://nn.cs.utexas.edu/downloads/papers/stanley.ec02.pdf) paper, but some doubts are still bugging me, so I have two questions.
  
  1. When do mutations occur? Between which nodes?
  2. When mating, what happens if 2 genes have the same connection but a different innovation number? As far as I know, mutations occur randomly and thus it is possible that 2 genomes have the same mutation.
  
  **Tags:** neural-networks, genetic-algorithms, evolutionary-algorithms, neat, neuroevolution
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2017-01-13. Score: 2
  
  > When do mutations occur and between which nodes?
  
  There are two types of mutations in the *NEAT* model, each of them appears randomly during one epoch on different individuals; the number of structures affected by mutations may vary depending upon the nature of the problem.
  
  * A new gene/node is added to the structure and properly linked.
  * A new connection between two nodes is added.
  
  > When mating, what happens if 2 genes have the same connection but a different innovation number?
  
  During a single epoch/generation every mutation is tracked and if the same mutation appears it can't have the same global *innovation* number. *Same mutation, same innovation number.* In that way, during the mating phase, there is no decisional problem which leads to prefer one structure to the other.
  
  
  ---
  
  