Martian (All Tomorrows)

The Martians were the first extraterrestrial posthuman species in Nemo-Ramjets All Tomorrows.

Biology
Biologically, the Martians were similar to the humans of Earth, but hundreds of years in the lower gravity of Mars caused them to grow taller and thinner. Together with some degree of genetic engineering, they have almost become their own species.

Colonialization of Mars
After the eventual political unification of the human race, they were finally able to colonize Mars. This was driven by the weakening of the environment by a population size of 12 billion people on Earth.

The first step was to create a breathable atmosphere, which was achieved by bombarding Mars with genetically tailored microbes. Those took centuries to turn the atmosphere of Mars into something that humans could breathe. After that, oceans were created and genetically modified versions of terrestrial flora and fauna was brought to the planet.

Mars was then colonized in one-way ships packed with colonists. For several hundred years, Mars prospered, but was never as economically advanced as earth. Earths businesses relocated their environmentally damaging industries to Mars to spare their own tired biosphere, and Earth's ecology prospered.

Martian Americans
After some time, the inhabitants of Mars began to develop their own cultural identity as Martian Americans. This was not only a cultural difference, but also a biological one. A combination of genetic engineering and natural evolution changed the Martians body frames to look more spindly due to the lower gravity on Mars, which made them essentially their own human race.

Almost since its establishment, Martian culture was suffused with an explicit theme of rebellion against Earth. Songs, motion pictures and daily publications repeated these notions again and again until they became internalized. Earth was the old, ossified home that held humanity back, while Mars was new; dynamic, active and inventive. Mars was the future.

Civil War
Roughly 1000 years from now, Mars banned nearly all trade and travel with Earth. This was the death sentence for Earth, environmentally and economically. Because essential trade was still permitted, nobody would have to starve, but the ban cost the people of Earth roughly a third of their yearly income.

This was the straw that broke the camels back. Earth declared war on Mars. The war was mostly fought by drones which were programmed to do as much damage as possible to the other side. Phobos, one of the moons of Mars, was destroyed and rained down on Mars as meteorites, while an impact on earth killed off a third of its population.

Aftermath
After the death of about eight billion people, both planets finally made peace and founded a united solar system. Both sides agreed, that massive changes were necessary to secure peace between the planets, and through genetic modification, the Star People were created as a new, united humanity.