Humans

**Humans** (Latin: *Humanae*) are a carbon-based humanoid species of apex predators native to the planet of Terra in the Sol system. The Humans are the rulers of a 1,205 lightyear realm (in radius), The Conglomerate, and are known galaxy-wide for their abnormal rate of technological progress and territorial expansion.

## Biology

### Appearance

Humans are a humanoid species with two arms, two legs, and a head, with all major organs located within the abdominal cavity serving as their center of mass. The human species is divided into two sexes; male and female, with a low rate of sexual dimorphism within the species as a whole. Males tend to be taller, stronger, and more heavily built, while females are shorter, slender in appearance, and generally weaker than their male counterparts. Both sexes possess hair on the top of their heads, on top of genitals, and for males: facial hair and chest hair. Human females have a hourglass figure, with their breasts protruding from their chest, the abdomen shortening when it comes to the waist, and widens out into the hip and thighs, where most female fat and muscle is stored. Males, on the other hand, are much more muscular and have an inverted triangle shape, with the chest narrowing down to the hip. Humans are genetically diverse by interstellar standards, having hundreds of ethnic groups; and along with these, hundreds of cultures, however, due to the events of the modern era, almost all cultural boundaries are now gone, and with globalization, ethnic differences began to decline, as genetic diversity averages out.

### Physiology

#### Nervous system

The nervous system consists of the central nervous system (the brain and spinal cord) and the peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The brain is the organ of thought, emotion, memory, and sensory processing, and serves many aspects of communication and controls various systems and functions. The special senses consist of vision, hearing, taste, and smell. The eyes, ears, tongue, and nose gather information about the body's environment respectively, and are all connected to the brain. Almost every organism on the Human homeworld, Terra, has a brain or similar nervous system. In addition, the brain also has command over all other organs within the human body. In a way, the brain acts as a control center of the human body all of the nervous system is connected to it. The nervous system extends to the ends of the human body. At the cellular level, the nervous system is defined by the presence of a special type of cell, called the neuron. Neurons have special structures that allow them to send signals rapidly and precisely to other cells.

#### Musculoskeletal system

The musculoskeletal system consists of the human skeleton (which includes bones, ligaments, tendons, and cartilage) and attached muscles. It gives the body basic structure and the ability for movement  The bones provide stability to the body. Muscles keep bones in place and also play a role in the movement of bones. To allow motion, different bones are connected by joints. Cartilage prevents the bone ends from rubbing directly onto each other. Muscles contract to move the bone attached at the joint. Each bone in the skeleton contains two forms of tissue: compact (dense) bone that is relatively solid and spongy (cancellous) bone that forms an open network of struts and plates. Compact bone is found on the external surface of the bone. Spongy bone is located inside the bone. The proportion of compact and spongy bone varies with the shape of the bone. Compact bone is thickest where stresses arrive from a limited range of directions. Spongy bone is located where bones are not heavily stressed or where stresses arrive from many directions. In addition to their structural role, the larger bones in the body contain bone marrow, the site of production of blood cells. Also, all bones are major storage sites for calcium and phosphate.

The central structure of this system is the Spine. Muscles keep bones in place and also play a role in the movement of bones. To allow motion, different bones are connected by joints. Cartilage prevents the bone ends from rubbing directly onto each other. Muscles contract to move the bone attached at the joint. This system can be split up into the muscular system and the skeletal system. The muscles in turn are mostly controlled by the nervous system, with the exception of the autonomous heart and lung muscles. Humans also have a dense cord of nervous tissue called the spinal cord that functions primarily in the transmission of neural signals between the brain and the rest of the body; but also transmits motory and sensory information. Leaving out the reproductive system, this is where most sexual dimorphism is placed. Human males are on average 5' 7" and females are 5' 4". In other words, males on average, are 10% taller than females. Along with this, males also contain 10% more muscle than females. Male fat and muscle is stored in the abdomen, while female fat and muscle is stored in breasts, buttocks, and thighs.

#### Circulatory system

The circulatory system or cardiovascular system comprises the heart and blood vessels (arteries, veins, and capillaries). The heart propels the circulation of the blood, which serves as a "transportation system" to transfer oxygen, fuel, nutrients, waste products, immune cells, and signalling molecules (i.e., hormones) from one part of the body to another. The blood consists of fluid that carries cells in the circulation, including some that move from tissue to blood vessels and back, as well as the spleen and bone marrow. This system is driven by the heart, which replenishes blood with oxygen and controls the movement of blood. In summary, it transports nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilizes temperature and pH, and maintain homeostasis. The most abundant cells in vertebrate blood are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates oxygen transport. It is bright red in color when replenished with oxygen, and is a dark red when not. The human heart beats approximitely 60 beats per minute on average.

#### Respiratory system

The respiratory system consists of the nose, nasopharynx, trachea, and lungs. It brings oxygen from the air and excretes carbon dioxide and water back into the air. Respiration takes place in the respiratory organs called lungs. The passage of air into the lungs to supply the body with oxygen is known as inhalation, and the passage of air out of the lungs to expel carbon dioxide is known as exhalation; this process is collectively called breathing or ventilation. In humans and other mammals, the anatomical features of the respiratory system include trachea, bronchi, bronchioles, lungs, and diaphragm. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveoli (air sacs) in the lungs. If liquid is taken into the lungs, it results in drowning. This system also allows Human speech.

#### Digestive system

The digestive system consists of the mouth including the tongue and teeth, esophagus, stomach, (gastrointestinal tract, small and large intestines, and rectum), as well as the liver, pancreas, gallbladder, and salivary glands. It converts food into small, nutritional, non-toxic molecules for distribution by the circulation to all tissues of the body, and excretes the unused residue out the anus. This takes at least a day, and at most 72 hours. Food enters the body from the mouth and is chewed by omnivorious teeth. It travels down the esophagus until it reaches the stomach. Chewed food is finally dissolved in the strong acidic gastric acid sitting at the buttom of the somach. Following this, food is brought to the small intestines, where nutriens are extracted, goes through the large intenstine, which deals with the moisture in food, and is secreted out of the rectum. The second largest organ in the human body, the liver regulates most chemical levels in the blood and excretes a product called bile. Bile helps to break down fats, preparing them for further digestion and absorption. All of the blood leaving the stomach and intestines passes through the liver. The liver processes this blood and breaks down, balances, and creates nutrients for the body to use.

#### Immune system

The immune system consists of the white blood cells, the thymus, lymph nodes and lymph channels, which are also part of the lymphatic system. The immune system provides a mechanism for the body to distinguish its own cells and tissues from alien cells and substances and to neutralize or destroy the latter by using specialized proteins such as antibodies, cytokines, and toll-like receptors, among many others. This system is the only defense from hostile pathogens within the body, whether it is bacteria, a virus, a parasite, or any other dangerous pathogen. The main cell of this system is the white blood cell, produced in bone marrow, which in coordination with the rest of this system, fights off hostile pathogens within a human body, ranging from cancer to bacterial infection.

##### Lymphatic system

The main function of the lymphatic system is to extract, transport and metabolize lymph, the fluid found in between cells. The lymphatic system is very similar to the circulatory system in terms of both its structure and its most basic function (to carry a body fluid and hormones). This system coordinates greatly with the immune system, serving as the primary communication method.

#### Endocrine system

The endocrine system consists of the principal endocrine glands: the pituitary, thyroid, adrenals, pancreas, parathyroids, and gonads, but nearly all organs and tissues produce specific endocrine hormones as well. The endocrine hormones serve as signals from one body system to another regarding an enormous array of conditions, and resulting in variety of changes of function. There is also the exocrine system. The most notable use of this system is puberty and weight.

#### Integumentary system

The integumentary system consists of the covering of the body (the skin), including hair and nails as well as other functionally important structures such as the sweat glands and sebaceous glands. The skin provides containment, structure, and protection for other organs, but it also serves as the most important sensory interface with the outside world. Nails protect the fingers and toes, and with the former, helps to pick up objects or scratch something.