CONJECTURE NUMBER TWO Perhaps the three varieties of pony can breed, but produce only infertile offspring. Unicorn + Earthpony = infertile hybrid. Earthpony + Pegasus = Infertile hybrid. Unicorn + Pegasi = infertile hybrid.
Perhaps the cake twins are the result of a pegasus-unicorn mix; that way they could be twins with each twin taking after one of its parents. No idea how the Cakes adopted them (no way that Earthpony + Earthpony = Unicorn/Pegasus twins; and Mister Cake's explanation is extremely sketchy and just screams "shenanigans" to me).
CONJECTURE NUMBER THREE: The three pony breeds can interbreed; with the following results.
Male Pegasus + Female Earthpony = Pegasus.
Male Earthpony + Female Pegasus = Earthpony.
Male Pegasus + Female Unicorn = Unicorn.
Male Unicorn + Female Pegasus = Pegasus.
Male Unicorn + Female Earthpony = Earthpony.
Male Earthpony + Female Unicorn = Earthpony.
So, in Earthpony + Pegasus pairings; the offspring are the breed of the father. In Pegasus + Unicorn pairings; the offspring are the breed of the mother. In Unicorn + Earthpony pairings; the child is an Earthpony.
That gives Three ways an Earthpony can happen, Two ways a Pegasus can happen; and One way a unicorn can happen. Given that Unicorns seem to be the most powerful (given magic), followed by pegasi (given speed and flight), followed by Earth ponies (physical strength, endurance); those ratios seem likely to create some sort of balance of power.
This also allows for the theory that Flutttershy's mother was an Earth Pony. However, there is still no way for Earthpony + Earthpony to equal Pegasus/Unicorn twins.
If anyone else wants to make charts of dominance, they are welcome to try.
edited 11th Feb '13 7:46:23 PM by ATC
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