Human

**Humans** (*Homo sapiens*) are the most abundant and widespread species of primate, characterized by bipedalism and large, complex brains, enabling the development of advanced tools, culture, and language. Humans are highly social and tend to live in complex social structures composed of many cooperating and competing groups, from families and kinship networks to political states. Social interactions between humans have established a wide variety of values, social norms, and rituals, which bolster human society. Curiosity and the human desire to understand and influence the environment and to explain and manipulate phenomena have motivated humanity's development of science, philosophy, mythology, religion, and other fields of study.

Humans are typically split into one of three demographics: terrans, those descended from Earthers; aresians, also called martians, descended from those born on Mars' colonies; and spacers, those born and adapted to live in outer space. They are the only known extant intelligent spacefaring race and one of only two known in history, the other being the extinct travellers.

## Biology

### Anatomy and physiology

Humans are mammals and are closely related to other large apes on the planet Earth. Like all placental mammals, they are warm-blooded and give birth to live offspring, and nourish their offspring with milk. They have five fingers, one being an opposable thumb. This hand structure aided them in making tools early in their history. Their circulatory system is closed and consists of one heart and a network of blood vessels. They have red blood due to their iron-based hemoglobin, as well as two lungs which breathe mainly a nitrogen-oxygen based atmosphere. Externally they have little body hair, requiring them to wear clothes to protect themselves from the worst of the elements. They are omnivorous, meaning that they will eat both meats and plants, as well as consume high calcium foods, such as the milk of other animals.

Their bone structure is calcium-based and is designed to withstand moderate stresses, but this varies between terrans, aresians and spacers; the same is true for their muscular system is. If in extreme distress, humans can tap into hidden reserves of energy known as an adrenaline rush that gives them drastically increased strength, a response known as the "Fight or Flight" reflex.

## Culture & Society

Humanity remains multicultural among its still marginally independent nations across the Settled Systems. Although humanity has adopted English as a *lingua franca*, other languages remain in use among human populations. Humans continue to practice a number of religions, although apart from several exceptions faith is largely considered a personal matter.

Males and females serve in the military in an equal capacity; showers and housing facilities are likewise shared. Cultural and racial hatreds are mostly absent, even in the face of the terran-aresian conflict.

Much like the cultural changes wrought by the colonization of the Earth in the past, space colonization has its own unpredictable effects on the cultures of colonial populations. As populations settle new worlds, cultures distort and sometimes amalgamate; however, it is common for the locals, whether they be terran, aresian or spacer, to consciously hold on to their Earth cultural heritage. This often takes the form of naming the colony world's locales after the native region or local mythology of its inhabitants.