Evolutionary biology is a core discipline in science. Thus knowledge of it is key to understanding other branches of biology. However, there are many authors who have reported difficulties in the teaching-learning processes of this content across several educational levels. In this chapter, the authors delve into pre- and in-service Spanish teacher perceptions about the cross-curricular nature of evolutionary biology by means of semi-structured interviews. All interviewees consider that biological evolution is a unifying content and so has to be approached in the classroom. Thus, treating this content as a central axis for biology could be the way towards an effective educational proposal for biological evolution, but how to reach and design it is still complex. With this in mind, this chapter describes a sequence of activities for secondary students aimed at addressing some learning challenges about biological evolution while considering its cross-curricular nature and its Spanish curricular framework.