News paper article 3 billion years later:
3 billion years ago tetrapedal primates divurged from man as they could run faster and hence escape predators and travel large distances. 2 billion years ago the proto horse divurged from these tetrapedal primates as the proto horse had become a more specialised runner and didn't have stringent dietary requirements.1 billion years ago the proto winged horse divurged from the proto horse as the wing like structures provided better aerodynamics while running and helped it glide over valleys and water bodies.50 million years ago the proto unicorn divurged from the proto winged horse and it was favoured by natural selection as it had a horn with which it could poke and kill other animals.10 million years ago the Unicorn divurged from the proto unicorn and it was favoured by nature as it had completely formed wings and a large horn on it's forehead and small girls thought it was cute.
Now we have fossil evidence for Man,tetrapedal primates and horses and scientists are still searching for the rest.
Primates don't just change into horses.
I'm too tired for this right now.