In a time long forgotten, before even Celestia and Luna were alicorns, there was a clan of earth ponies who had managed to accomplish the impossible. Since time began it was thought only unicorns could do feats of magic; and as such boasted, just as the pegasi did about their flight. But through ways and arts passed down from family to family a select few earth ponies managed to do magic without the need of horns.
However their secret spread to other unicorn clans; and were soon attacked. Despite not having the same restrictions as unicorns did, the earth ponies parished. The bodies were burned; and so we're their secrets.
If only the clan leaders hadn't succeeded in their most secret spell; and their child survived.