Resian IV is a harsh and brutal world. It freezes at night and cooks during the day, both of which last nearly four months. The native flora and fauna are hostile to human life. Its gravity is nearly twice that of most other colonized worlds. It was used as a prison planet and military training and testing facility.
Then contact was lost. Resian was left with no ships capable of interstellar travel. For the first year, the abandoned held out hope that relief would come. After that, hard decisions were made.
The military personnel and the surviving prisoners banded together for survival. When it became clear help would not come, the society segregated along gender lines. The comparatively few women moved into the caves and tunnels that had housed the prison and research facility, while the men went to the surface to find food.
Due to Resian’s nature and the lack of medical care, pregnancy and childbirth took a toll on the female population. At first, maternal mortality rates were one in five. For this reason, breeding became strictly controlled. As time passed, breeding rights became something the men had to compete to earn, ensuring only the strongest and best passed on their genes.
Culturally, they are tribal. They have no use for weakness. Due to the harsh realities of their world, they have no stigmata against cannibalism. Those who could not provide became provisions. What little government it has is matriarchal, ruled by a council of women that have survived into old age. They function as teachers and protectors of the young with their focus being on providing the children with the training they need to survive the brutal world. At sixteen, males go to the surface, and females join the breeding program.
This artificially enforced evolution combined with the slightly higher mutation rate forged the population of Resian into a subspecies of human. They are still fertile with homo sapiens, should they choose, yet have marked differences. Their vision is more acute, allowing them to also see into the infrared and ultraviolet spectrums, and they have enhanced night vision. They are extremely strong and hardy, capable of withstanding greater environmental extremes.
When Resian was rediscovered, first contact did not go well. This lead the explorers to dub Resian an hell planet occupied by the infernal. Despite the best efforts of level-headed scholars, the name ‘homo infernal’ stuck.