Human

### Hair Colors

Pale gold, oranges, browns, and blacks. Often lightens with age to the point of becoming gray or white. Individuals often artificially color their hair to many shades of the human visual spectrum or matching other natural hair colors.

### Distinctions

Great ideological, technological, and physical diversity, great stamina, and physical durability.

## Other Info

### Homeworld

Native to Earth in the Sol system. Most populated known colony is Venus in the Sol system.

### Interplanetary Travel...

1969 CE: Apollo 11 to Luna.2030 CE: Privately funded missions lead humans to Mars.

### FTL Travel...

2120s CE: First successful tests of Alcubierre warp drives near Mars.

*H. sapiens*, colloquially known as Humans, is a species of sapient primates native to Earth in the Sol system. Since their departure from Earth in the 2030s onward, they have diversified into a number of different subspecies with traits specific to each.

## Anatomy

### Internal Anatomy

#### Skeletal Structure

Humans are humanoid, and are the basis for the name for the body plan in their languages, describing a bilaterally symmetrical bipedal tetrapod with five extremities, two legs, two arms, and a head that is not also a part of the torso.

Each limb has three segments, known as the leg or arm, which has one bone, the foreleg or forearm, which has two, and the hand or foot, which has more than a dozen to allow for articulation of each of their 20 digits. Each hand and foot has 5 digits each.

The human torso is composed of three groups of bones. The spine, which serves as a core for the entire skeleton, directly attached to the rib cage and the pelvis. The rib cage is made of many flat bones that serve to protect the organs immediately required for proper functioning of the body, those being the heart and lungs, and the pelvis serves to support the abdominal organs and as a place for the legs to attach.

Male pelvises are conical, while female pelvises are wider and bowl shaped, with a larger opening to allow the passage of infants during birth.

Below the pelvis is the coccyx, the diminished vestigial remnants of a tail still present in non-ape Earth primates.

At the top of the spine is the skull, composed of two primary bone groups, those being the cranium and the mandible. Each meets at the sides of the head and mate together via the teeth.

#### Central Nervous System

The human central nervous system is composed two parts. The primary component is the brain, responsible for maintaining centralized and coordinated control of the body's organs and muscle tissues by producing electrical signals and secreting hormones.

Second is the spinal cord, which serves to deliver signals from the brain to the rest of the body and to hold reflex loops, a short nerve circuit that is responsible for reflexive actions such as drawing a hand away from a hot surface without requiring a signal to be sent all the way to the brain and back to the muscle tissue.

#### Vascular System

The vascular system is responsible for the transport of blood and lymph throughout the body, with red blood cells oxygenating tissues, white blood cells used to fight infections, platelets used to stop bleeding by clumping together as clots, plasma to carry all of these cells through the body, and lymph to carry recycled blood plasma from the kidneys.

A four chambered heart works to pump the blood throughout the body, taking in deoxygenated blood from the veins, moving it to the lungs to be reoxygenated, and sending it out through the arteries.

### Reproductive anatomy

The human female reproductive system is centered upon the uterus, which branches from there into a pair of fallopian tubes which end at the ovaries, female gonads responsible for the production of eggs. Below the uterus is the cervix, an opening that connects it to the vaginal canal.

Male reproductive anatomy begins with the testes, which produce spermatozoa. From there, it enters the seminal vesicles and the prostate, which produce the fluid components of semen. When stimulated, this sperm enters the urethra and is expelled from the penis. This is mechanically intended to impregnate a female by way of vaginal intercourse.

Despite the ultimate purpose of intercourse being procreation, the majority of sexual encounters are not intended to achieve that end, instead serving for the entertainment of the parties involved, a deepening of the intimate bond between lovers, or simply for stress relief.

#### Skin

The skin serves as an outer covering for the body, protecting the interior structures of the body from radiation and physical damage.

Human skin is, by default, a shade of pale pink, as can be seen in individuals with albinism. Depending upon ancestry and ultraviolet radiation exposure, skin cells known as melanocytes produce varying levels of melanin, a brown colored pigment. It serves to protect cellular nuclei against UV radiation, and causes the dark tones of both the skin and irises of the eyes.

On its surface is a number of small glands, pores, and follicles that are responsible for the production of sweat, oil, and hair. The prehuman ancestors of modern humanity had far more hair than modern humans do. The remnants of this body hair primarily serves the purpose of an early warning system for unwanted flying pests lighting on the body.

#### Head

Human heads have the greatest concentrations of hair. The follicles on the face and head are capable of producing thicker hair than anywhere else on the body. The thick hair on the head protects the crown of the head from the sun, and the brows and lashes protect the eyes from debris and sweat.

The eyes, resting just above the midpoint of the face, are responsible for sight, with variations in the shape of the eye requiring the use of corrective lenses or surgical treatments to achieve focused vision. The sclera makes up most of the exterior surface of the eye and is white in color, with the exceptions of numerous small red blood vessels.

The iris is the colored part of the eye, which opens and closes as ambient light levels increase and decrease. The color of the iris varies depending on genetic background, and can be shades of brown, green, blue, gray, and hazel. The pupil is a hole in the iris, which allows light inside to stimulate the retina, which allows the brain to interpret the light as images.

The nose is a cartilaginous structure at the face's center, featuring two holes to allow the passage of air into the lungs. The nasal cavity houses the olfactory nerve, which detects chemicals in the air and enables the sensation of smell.

The mouth is located at the face's bottom and is surrounded by the lips, thin and flexible skin that serves as an intermediary between the skin and mucous membranes found on the interior surfaces of the body. They hold food inside the mouth, keep unwanted items outside, and are used as a component of both verbal and nonverbal communication. The lips are also an erogenous zone, as humans are able to derive pleasure from their stimulation in intimate situations.

Inside the mouth is the tongue, a strong and dexterous muscle which is articulated along with the jaw to chew food, and in concert with the lips to produce the various shapes required to produce speech. Its surface is coated in small clusters of cells that are responsible for the sensation of taste.

Teeth serve as the surfaces against which food is chewed to aid in digestion. The teeth have a number of shapes which serve a number of purposes, from the front teeth, incisors and canines, used to chop and tear, while the rear molar teeth are used to crush and grind.

The amount of teeth an individual has varies depending on age. Young children have 20 deciduous teeth, which fall out and are replaced with permanent teeth, which number between 28 and 32 depending on the degree of third molar hypodontia. In one quarter of the mouth, there are two blade-like incisors, one pointed canine tooth, two premolars, and two to three molars.

On either side of the head are the ears, serving to funnel sound waves into the ear canal, where it will be interpreted by the brain.

#### Torso

The shape of the human torso is largely driven by their skeletal structure, from the shoulders and ribs to the stomach and pelvis.

The majority of the large organs in the body are contained within the torso, including the middle and lower digestive tract, the respiratory system, the heart and kidneys, the liver, the gallbladder, the spleen, and many more.

On the chests of females are the mammaries, or breasts, a secondary sex characteristic that produces milk used to feed infants until they are weaned. This milk is fed through the nipples. Human males have vestigial nipples due to androgen production being responsible for human sexual dimorphism. Individuals with XY chromosomes can develop typically female features if deprived of androgen during gestation, and the opposite is true of an XX individual should androgen be abundant instead of estrogen.

The external reproductive anatomy of both sexes lies between the legs, though this is more obvious in males, with both the penis and scrotum, which contains the testicles, resting below the groin. External features of the vagina, including the labia and clitoris, are visible externally instead.

The navel, located between the abdominal muscles and roughly level with the waistline, is a remnant of a human's time in their mother's uterus, and served as the attachment point for the umbilical cord used to feed nutrients to the developing fetus.

#### Limbs

Human limbs, as mentioned in "Skeletal Structure", are primarily composed of three segments, joined at the shoulders for the arms and at the hips for the legs, jointed at the elbow/knee, and again at the wrist/ankle. Each arm ends with a hand, which possesses four fingers with three segments each and an opposable thumb with two. The same number of segments exists in the corresponding toes.

## Genetic Variations

The world humans first colonized other than their moon, on which no humans were born for decades after the established bases, was Mars.