Complex sentence: In extrinsic evolution only the final best solution in the final population of the evolutionary algorithm is physically implemented, whereas with intrinsic evolution every individual in every generation of the EA's population is physically realized and tested.
Split into simpler sentences: In extrinsic evolution only the final best solution in the final population of the evolutionary algorithm is physically implemented. In intrinsic evolution every individual in every generation of the EA's population is physically realized and tested.