Bio-inspired metaheuristics like evolutionary algorithms are often applied to highly complex problems where good solutions must be obtained in short time. Parallelization is a popular way for speeding up these optimization tasks. Parallel evolutionary algorithms distribute the evolution on subpopulations, each evolving on a distinct processor or "island." Good individuals are exchanged between the islands with respect to a given communication topology connecting the islands. I will review recent theoretical advances on the computational complexity or running time of parallel evolutionary algorithms, with a focus on possible speedups in terms of the parallel computation time.