Okay so there’s actually very little to substantiate my little theory, but I think I’ve really uncovered something.
Over the years I’ve been watching Calista Flockhart and Fiona Apple very closely - and only just recently have I uncovered their little secret. Aha! They are actually twins, separated at birth!
Here’s the evidence I’ve collected so far:

1. Both bear a striking resemblance to each other
2. Both wafer thin
3. Both big in the 90’s but let careers wain in recent years because of “the Man” - i.e. Sony and Harrison Ford
4. Both very private and make rare public appearances
5. In their respective artforms, both play the part of moody, empowered, post-feminist saps

More to come… just remember you read it here first!