Mercury was moved out of its original orbit in 2321 CE to aid in the terraforming of Venus. This caught the attention of a couple massive corporations back on Earth who sent out teams of their own to begin terraforming procedures on Mercury as well. Terraforming began in 2335.
Gases collected from Saturn, Uranus, Neptune, and a few of their moons were imported to help create a new atmosphere. Over the next two hundred years small plants and animals were slowly introduced. By 2613 the moon had been completely terraformed.
Fron 175600 to 193757 Mercury was moved back into solar orbit to stabilize Venus' rotation once again.
As with Venus, some of the ancestors of the now five billion inhabitants of Mercury came from the equatorial regions of Earth, but surprisingly most came from Venus. Mercurians, while having darker skin like Venusians, are also taller and weaker due to moon's weaker gravity. Also because of the weaker pull, many inhabitants have opted for genetic engineering and have implanted wings onto their person, allowing them to fly around. This has led to genetic incompatibility with base humans and other complications.
Mercury's trees and animals there are also much taller than their Venusian parents, although they are quite different from those on Luna.