Human

Humans are a species of sapient, bipedal mammals native to Earth.

Description
Human beings are somewhat variable as a species, but possess a number of features shared by all normal, healthy individuals. Humans are humanoid tetrapods, walking fully upright on their back legs. The front limbs are specialized for the grasping of objects, ending in flexible hands with five fingers each. The torso is long, thicker in males but narrow at the waist in females. At the top of the torso is a short neck, which supports the head.

The face is characterized by having two eyes just below the forehead, with a pronounced nose between and below them both. The mouth lies below the nose, and is covered on both sides by cheeks which contain food during chewing. The mouth contains teeth of different sizes and shapes, used to process the varied diet of humans.

Unlike many other mammals on their homeworld, humans possess little hair. The majority of this is found at the top of the head, with small patches under the arms and around the genitalia of adults. Adult males also possess hair at the front of the torso.

On average, humans males stand about six feet tall, while females are generally shorter, often between five and six feet in height. Differences abound even in healthy and non-deformed individuals, however, particularly between different ethnic groups.

Color is another area in which humans vary--depending on ethnicity, possible skin tones include white, brown, yellow, and reddish. The colors are usually based on the region of the planet the ethnic group originated in.

Internal Physiology
Humans possess a sturdy, largely calcium-based skeletal system. The torso is filled by a skeletal rib cage, which protects the single heart and double lung system. Below this is the majority of the digestive tract, consisting of an acid-filled stomach and a very long, coiled intestinal tube.

Human muscles are spread throughout the body, often working in pairs or sets. The muscles pull bones and organs, but cannot push. They are connected to bones by ligaments.

Diet
Omnivores by nature, humans are equipped with a flexible array of teeth capable of processing a wide variety of foods. The rest of the digestive system only enhances this adaptability, and is one of the factors that allowed humans to first spread over their homeworld.

The three macronutrients used by humans are fats, proteins, and carbohydrates. Fats and proteins are used in the construction of cells, while carbohydrates are used to produce glucose, which is then converted into energy. Although fats and protein are absolutely essential to human life, carbohydrates are not, as the body can convert fat into glucose in the absence of carbohydrate material.

Reproduction
Humans reproduce by sexual means, with males and females mating to produce offspring. In this process, the genes of both parents are combined, producing a unique individual with attributes of both parents.

Young are gestated for nine months in the mother's womb, after which they are expelled through the birth canal. Bipedal locomotion and enhanced brain size makes childbirth more difficult for humans than for other animals, and in historical times it was not uncommon for females to die in the process. Children are typically raised by both parents and possibly an extended family, although familiar size has grown smaller as human society has progressed. Offspring become sexually mature at around thirteen years of age, although coupling usually does not take place until later in development.