TALENT or GENIUS?

What is genius? How is it different from talent? Is it a matter of degree, or is it something altogether distinct?
In the past week on Facebook—admittedly not the most elevated forum, though I like to think that most of my friends are fairly bright—I have read that the following people are geniuses: JK Rowling, Prince and Stevie Wonder. I also read that Taylor Swift is extremely talented: she must be, said my friend, an intelligent person, because she is so widely popular. (I had perhaps foolishly, and certainly thoughtlessly, given the opinion that she was ‘completely talentless.’)

For a number of reasons, these comments disturbed me, and forced me to consider—yet again—whether it is possible to make any objective evaluation of the talent of an artist—Aesthetics 101—and also, if it’s possible to discuss the subject without simply getting into a curmudgeonly rant about declining standards, whether there is such a thing as genius, and if so, whether we might be able to define it