Why primaries to select the leader? Explanations to the adaptations of the parties. The Spanish case.

In Spain, in 2010, only a minor party had held primaries to elect its leader, at the national level. In 2018, the four main parties would have already experimented with the primaries, in one way or another. Beyond the visible change in procedure, what are the explanations for these adaptations? Taking into account the circumstances of each party at the time of adopting the change, at three different levels –political system, party system and intraparty system-, we can reach deep explanations for the behavior of these political organizations. The crises of inter-party competitiveness, as a simplification of multiple possible adversities, is exposed as the main explanatory variable. Another factor such as the contagion effect, not only between parties, but also between party levels, is also explored at a theoretical level. The appearance and rise of three new parties –Podemos, Ciudadanos and Vox- in a very short period of time makes the Spanish party system a case of special interest to observe the dynamics of the parties in a key element such as the election of a leader.