What Darwin called varieties now called subspecies. are important from an evolution point of view because a group becoming isolated in the sense that they stop breeding with others is a critical step. Changes in circumstances for the isolated group are cited as an aid to their developing into a new species.
Human activity can result in a group becoming isolated and can change circumstances or the environment for a subspecies, Human activity can also result in the merging of two species that are still close enough to interbreed - perhaps they should be regarded as a subspecies of each other..Grey Duck or Pacific Black Duck and Mallards are examples.
Darwin didn't have the knowledge of genetics and continental drift that we have today or access to the fossil record that is available today but still managed to work out the process that he called evolution - a true genius in my opinion.
