This paper discusses the design of multiple input multiple output (MIMO) antenna systems and proposes a genetic algorithm to obtain the position and orientation of each MIMO array antenna that maximizes the ergodic capacity for a given propagation scenario. Our results show that the electromagnetic coupling effect can be exploited by the optimizer in order to decrease signal correlation and increase MIMO capacity. A comparison among uniform linear array (ULA), uniform circular array (UCA) and the GA-optimized array is also carried out.