Fig 1: A Human of Earth. The human pictured uses a local written language to produce works of art and to earn credits for the negotiation and acquisition of foodstuffs and other goods. Mature humans will usually engage in one or more ongoing occupations during their years of health, both contributing to their societies and earning credit for future negotiations.
The "Human" (/(h)yo͞omən/), at a glance.
The picture above depicts a "Human" of the terrestrial planet that humans call Earth (for more context, see entry for Earth's star system). That which is not a part of the human in the image has been blurred. Humans are all outwardly identical to each other, sharing 99.9% the same genetic material. The small variation remaining is capitalized upon by evolutionary processes at work in all creatures on Earth. Through sexual reproduction, large, multi-celled Human Terrans produce (over generations) slight genetic variations that bolster collective immunity to threats both biological and physical. Two sexes result, one having a flesh proboscis for injecting genetic material and the other an internal gestating organ. The latter gestates a developing fetus internally for nearly one Earth year, then both foster the new human externally for up to twenty. Humans are the dominant species of Earth by influence and have very recently reached nascent space-faring status. They as of yet remain located entirely within the gravity well of their home world.
At birth, the human will develop slowly compared to other Terrans, usually taking over ten Earth years to reach sexual maturity. The structure pictured is the highest limb ("Head") of the human (there are five limbs in total) and the most important. Inside the protective bone and skin of this limb is where the human's sensory processing organ is located and the substructures on its surface are used for intraspecial communication. Muscles contract in sequence to shift and distort the soft skin that overlays the calcium-based internal skeletal features, providing a vast potential for communicating emotions and information, including but not limited to: status, intimacy, anger, fear, surprise, joy, and attraction. The individual in the picture is covered in hairs of various lengths and thicknesses (hair colour and texture vary) with different purposes. Hair performs roles such as signalling maturity, display of status for courtship rituals (humans are very social and have elaborate communities and social language), wicking of moisture, trapping of heat and physical protection. Sight organs appear in pairs, allowing depth perception. They are located centrally on the front of the head, identifiable by a prominent, coloured iris surrounded by white tissue. The organs' capabilities vary slightly but can generally detect electromagnetic radiation with wavelengths between 390-700nm. On the side of the head are two vertically-mirrored outcroppings that collect and funnel sound waves to receptors within the bone structure. Near the front, below centre, is a complex of odor and taste-sensitive centres, the latter of which has evolved to both grind up foodstuffs (using protrusions of bone) and to allow the formulation of sounds that enable much more nuanced expressions of thought than what can be conveyed using the muscular deformations. Humans inhale through this complex the ambient atmosphere (harvesting gases used for metabolism), then expel unused gas and waste. Muscles in the connective trunk between the central organs and the outlying head can modulate the atmosphere passing through, producing a range of bleats, chirps, chants and chuffs that are further clipped or pronounced by the workings of the taste centre. The scent-detecting organ is diminished in power in comparison to many other species of Terran but still performs a function of alerting the human to volatilized chemicals that can signal threats, potential mates and/or food in the environment. The head is self-identified as the human centre of being and thought, and is believed to be hierarchical over the other features of the body. Indeed, nearly all bodily functions, movements and activities are directly initiated and controlled by the relatively large processing organ contained in the head.
Across the lower part of the image, one can see a material draped on the human's protective outer organ. Most humans will cover themselves with fabrics as part of ongoing negotiations of status and courtship rituals. The fabrics may also serve to protect human wearers from climates that their bodies are ill-adapted for. Humans are naturally a subtropical creature and will quickly succumb to death in most latitudes of the planet when deprived of their protective fabrics and other tools (on average, across the planet, humans will live for seventy Earth years). It has been noted that the unusual-for-Earth operating intelligence of humans has been achieved by random genetic evolution, and thus some humans are far better equipped in their abilities to survive hostile climates than others. Tools in general have served to drastically level the capabilities of humans to thrive despite local conditions, resulting in a shift of primary evolutionary force from natural pressure to sexual selection. After observing recent trends amongst human societies, it is predicted by some that soon the humans will begin applying their ever-subtler tools and knowledge to the modification of their bodies, at which point they may enter a phase of almost no natural selection at all. This remains a popular theory among researchers, but one still receiving criticisms at the time of this writing.
Humans as a whole are roughly average in disposition and temperament when compared to other lifeforms of similar cognitive capacities. A noteworthy strain of curiosity is likely the result of the nomadic, persistence-hunting that characterized their species at the time of its earliest discovery. A need for movement and for creative negotiation of the complex tasks of tracking and predictiing the movements of prey has likely selected favourably for strong curiosity and talent for abstract thought. This adaptiveness has meant that Humans have developed their technologies exponentially, already consuming at the limits of their home world after only a few million local years. Humans will likely begin to expand their territory across the other worlds of their solar system (which is unusually barren of life, with the exception of one moon). Though they are not expected to achieve interstellar travel within the near future, they have been flagged as a "watch" species on account of the ongoing exponential pace of their development.