In this paper, we present a binary Biogeography-Based Optimization (BBO) algorithm-based low-complexity interference aware relay assignment scheme with power control for a cognitive radio network with one source node, multiple relays and multiple destination nodes. Optimally relay assignment using the Exhaustive Search Algorithm (ESA) has a high computational complexity that grows exponentially with the number of relays and users. We formulate the jointly relay assignment with source and relays' power allocation as a mixed integer non-linear programming problem which further reduces to an integer programming problem. We employ BBO as one of the novel Evolutionary Algorithms (EA) under the broad category of Swarm Intelligence and present a BBO-based relay assignment scheme with discrete power control at source and relays for the integer programming problem. We present a low-complex migration model for partial immigration-based BBO, and simulation results show that its performance is close to the optional ESA.