In this talk, I will present how evolutionary robotics can be used for designing and studying collective (robotic) systems. This talk will focus on how evolutionary robotics for collective systems can be used both for engineering (as a design method) and biology (as a modelling and simulation method). In particular, I will describe our recent works on (1) the challenge of the evolution of behaviour specialisation in swarm robotics and (2) the (under-estimated) importance of the mechanistic aspects in the evolution of cooperation in biological systems.