The classification of the x-NEAT methods found by the review protocol is presented in Table 6; only two methods, TMO-NEAT (Marzullo et al., 2017) and Cascade-NEAT (Kohl and Miikkulainen, 2009), could not be categorized into any of the proposed clusters. It should be noted that this table is not an exhaustive list of all the methods in the field, just the ones that are returned by the inclusion and selection criteria of the protocol. The table is preferably read column-wise: a single tick in a column does not at all mean that the indicated paper is the only paper addressing the category. In the Appendix, we present detailed answers of the three RQs (principles, encoding, and evaluation) for each method. Figure 1 presents the trajectory of the x-NEAT methods' evolution. This is a graphical illustration of how x-NEAT methods emerged from the original NEAT method, that is, which method is being extended by another.