<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>

CC BY-SA 4.0
2017-01-13T15:28:25.397Z
2019-07-07T18:57:44.867Z
2019-07-07T18:57:44.867Z
Lovecraft
<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>

<neural-networks><genetic-algorithms><evolutionary-algorithms><neat><neuroevolution>
What happens if 2 genes have the same connection but a different innovation number?
Miemels
# 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


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## 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.


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