Setting initial range in GA

If we set bounds in the initial range in population, let us say, from -1 to 1, can someone explain me how subsequent generations can contain points that don lie in that range. I have read about population diversity and how we select inital range by approximately knowing where is solution of a problem, but I didn't understand it completely. If I'm sure that solution lies in this area [-1,1] why would algorithm search for solutions outside that area? Please don't mind me, I'm still begginer. Thanks,bye!!