Why Scootaloo, one-third of the Cutie Mark Crusaders, is unable to fly like almost all other of Equestria's Pegasi.

After all, this apparent disability has been the occasional joke by her fellow CMCs Sweetie Belle and Apple Bloom.

My Little Pony Friendship is Magic has yet to disclose the identity of Scootaloo's parents (although I presume she's a single child, which can explain why she looks up to Rainbow Dash).

Could Scootaloo's parents, instead of two Pegasus ponies, include a Pegasus mother and an Earth Pony father? Or is that an Earth pony mother and Pegasus father?

Being partially descended from Earth ponies could explain why Scootaloo has trouble flying.

Then again, it's a bit of a problem to explain, for example, why Mr. and Mrs. Cake, two married Earth ponies, have a male Pegasus and female Unicorn as fraternal twin children (Pound Cake and Pumpkin Cake).