In list-based proportional representation systems the election of individual politicians largely depends on their rank position on the ballot. Party organizations therefore play a crucial role in determining which candidates will be elected, and incumbents have incentives to remain popular among party elites. Does this mean that candidate background characteristics are unimportant given party affiliation? We study this question using speeches from the Norwegian Parliament and recently developed techniques for measuring groups differences in high-dimensional choices. We find that the within-party polarization between men and women is of the same magnitude as the polarization between left-wing and right-wing parties. For the other background characteristics we consider -- age, urbanicity, and class background -- we find more muted differences within parties.