King Lear's Natural and Unnatural

I am very interested in the theme and element of natural and unnatural in the play, King Lear which is written by the famous and brilliant writer, poet and playwright, William Shakespeare. The element of natural and unnatural have been brilliantly depicted in both, main and sub plot of the play. In the main plot, the King, Lear has three daughters of whom he loves and this is natural.
But, what makes it unnatural is that Lear's two elder daughters, Goneril and Regan act as if they are not his natural and legitimate daughters. When Lear asks his daughters to profess their love to him, Goneril and Regan have professed their exaggerated, false love to him and in return, Lear has given them his kingdom. Only later, does Lear realises that they are liars, but it is futile. They never want their old, foolish father besides them. Only Cordelia, his last daughter proves to be loyal and love him in the true sense of love. Lear regrets that he has disowned Cordelia in the first place.
Meanwhile, in the sub plot of the story, the element of natural and unnatural have also been portrayed. These two conficting elements are depicted by Gloucester's sons, Edgar and Edmund who represent the opposing qualities, legitimacy and illegitimacy. Edgar represents legitimacy as he is the successor and the rightful heir to his father's possessions. Meanwhile, Edmund represents illegitimacy as he is the bastard son of Gloucester. Edgar is very kind and loyal to his father, but Edmund's lie has made him the betrayer in the eyes of Gloucester. In contrast, Edmund is an ambitious and evil son of Gloucester, betrayed his brother Edgar to fulfil his ambition.