The magical land of Equestria is known for many things, but mainly the uniqueness of its inhabitants. Concrete information about the physiology of the intelligent miniature equines who share the title of “dominant species” with a handful of other sentient creatures is frustratingly limited, but not nonexistent. These equines, more commonly known as Little Ponies, are unique in that they come in three wildly divergent phenotypes: Pegasus, Unicorn, and Earth Pony.
All three phenotypes share the same quadrupedal build. Additionally, all possess humanlike intelligence, enormous eyes capable of both 180 degree and binocular vision, and brightly colored coats and manes that appear to be unique to the individual. One individual's mane was even noted as having no less than six colors in sequential stripes. All ponies also bear some kind of design on both flanks. The ponies themselves refer to these as “cutie marks” and believe them to be representative of the individual's personality and/or talents.
Pegasus ponies, also known as pegasi, take their name from Hercules' winged horse in Greek mythology. As the name would suggest, they possess a pair of feathered wings and have the ability to fly. Exactly how these wings enable such feats as hovering and rapid acceleration is unknown; pegasus wings are ludicrously small. Interviews with the pegasi themselves on this matter have proved unhelpful. In the words of professional flier Spitfire, “How do I manage to fly? You might as well ask me how I manage to walk. We're born with it. Some of us can fly before we say our first words." Pegasus wings also give their owners the ability to interact with clouds in strange ways. Pegasi are often seen busying themselves by changing the weather over the towns where they live.
Unicorns, named for the single horn that each one possesses on his or her forehead, possess an even stranger power than pegasus flight. All unicorns are capable of telekinesis, along with reality-bending feats like visual illusions and teleportation. These feats are totally inexplicable by any currently known methods. Unicorns themselves call this ability “magic,” and many of them even develop specific “spells.” One such unicorn by the name of Twilight Sparkle offered a researcher named Dr. Hypha the chance to watch a demonstration. Twilight Sparkle's abilities were astonishing even by unicorn standards, and she revealed to Dr. Hypha that her ability was not a typical example—that she was extraordinary among unicorns.
Finally, ponies who possess neither wings nor horns are known as Earth Ponies. While Earth Ponies face little or no discrimination from their winged and horned peers, exactly what special qualities they possess that are analogous to flight or “magic” is unknown. A hint may be found in the fact that, stereotypically, Earth Ponies are skilled farmers and chefs. A stallion named Big Macintosh, though he insisted that he was too busy to speak to researchers, displayed the ability to harvest apples from a tree simply by bucking the trunk with his hind legs.
Researchers understand almost nothing about pony biology, but have had many chances to observe pony society. Entire books could be written about the ways in which ponies differ from humans, but a common value on friendship seems to be prevalent. Twilight Sparkle in particular had an almost religious belief in the power of friendship, insisting that the bond she shared with her friends was not only the source of, but also utterly synonymous with, her magic. There is currently no way to know exactly how meaningful this statement is, but we have little choice for now but to defer to her knowledge.