There's like a 10:1 ratio of females to males in Equestria, at least in the first few season which as we know, are the only canon ones. But we've also see in the show that mlp ponies are monogamous and only have a couple children on average, which means how do ponies keep their population up? The answer is simple: futa. Half the mares in Equestria are futa and that's why they are still called girls despite having dicks. But then the question remains, which of the mane 6 are futa? Rainbow Dash and Applejack for sure but who's the third one? Twilight? Pinkie Pie?