Human

"Homo sapiens; what an inventive, invincible species. It's only a few million years since they crawled up out of the mud and learned to walk. Puny, defenseless bipeds. They've survived flood, famine and plague. They've survived cosmic wars and holocausts. And now, here they are, out among the stars, waiting to begin a new life. Ready to out sit eternity. They're indomitable!"

- The Doctor (The Ark in Space)

Humans (Homo sapiens) are a species of bipedal sapient mammals native to planet Earth. They are omnivorous and generally believed to have descended from arboreal ancestors.

Biology
Humans have an erect posture, with two legs, two arms and a head which comprises the brain and most of the sense organs. Extraterrestrial species showing this same body plan, or a very similar one, are collectively known as humanoids. Although some humanoid races look almost exactly like humans, as is the case with Vulcans, they are often very different internally. Vulcans, for example, have green blood containing copper, while the Human blood is red and contains iron.

Humans are carbon-based lifeforms, and have an internal skeleton containing calcium phosphate, which gives the bones strength and durability. More than 60% of the Human body is composed of liquid water. Their circulatory system is closed and they have a heart and two lungs (though they are able to survive with only one lung), located in the chest area.

Humans have two pairs of limbs, the lower pair adapted for bipedal walking (legs) and the upper for carrying (arms).

Human arms end in hands. Hand are intricate arrangements of five miniature limbs that can be used as grapples, tweezers, clusters of feelers, baskets or semaphore machines. (Aliens often mistake human hands for symbiotic lifeforms on first contact: hands appear to have four limbs and a head, like the main body of the human; the hands operate machinery and perform all the recognizably intelligent actions, and the hands attempt to communicate in some sort of interpretive dance.)

Humans balance vertically on their legs. Human knees bend backwards. Human feet evolved from a second pair of hands, the feet can bear the human's weight, but cannot perform any of the actions of the true hands. However, though, hence, humans have also developed sufficiently to perform tasks using their feet as a matter of choice and need in place of the hands where absent.

Despite having evolved as a predatory species, Humans are generally considered weak and not well adapted to hunt without the aid of tools. Their canine teeth, for example, are not sharp like those of their evolutionary relatives, the other Earth primates, and their fingers and toes have nails, rather than claws. They can, however throw objects with unusual strength and accuracy, and an athletic human is a tireless runner. A human following you with a rock is extremely dangerous.

Humanity's greatest strength is their endurance. Being pursuit predators by nature, humans have several adaptations for such a lifestyle such as sweat glands and being mostly bare of hair. Even when compared to other Terran pursuit predators like wolves, a human's endurance is massive. With this endurance comes hardiness. Injuries such as broken limbs or large lacerations are often death sentences for other species while humans oftentimes live several years after receiving similar injuries though, thanks to their hyperactive scar tissue, leaves nasty scars.

Technology
Human technology is largely based on fire, textiles, ceramics, refined metals and woodwork. Wood is rigid plant matter. Humans cultivate useful plants and "tame" animals. Taming is the control of non-intelligent animals by befriending and selective breeding. Humans use simple biochemistry to repair and regulate their bodies. It is very common for humans to use floating vehicles. Humans' first priorities are weapons, the production of shelters, and the lighting of fires, to produce digestible food.

Humans extend their memories, communicate and perform mathematics by scratching and painting symbols onto objects. Advanced human civilizations begin with this practice. Humans' possessions and environments are often completely covered in these symbols. Humans record large bodies of knowledge in "books". Books are block-shaped objects made of hundreds of flaps: vast, hidden surface areas for symbols. However, in the late 20th and early 21st centuries humans began to store information on computers.

Advanced human technology includes: wheeled and flying vehicles; mining for metals and combustible minerals; organic chemistry (mostly the production of drugs, plastics and explosives); atomic fission; and a large variety of electromagnetic devices, including Von Neumann computers. Humans' use of biological machines does not extend beyond their taming technologies and experiments with microorganisms.

Humanity has had atomic weapons since 1945, but the majority of weapons used by humanity are chemical- and projectile-based with some electromagnetic alternatives, like the rail-gun.

Humanity entered the space age in 1957 with the launch of Sputnik, their first satellite. Since then humanity has launched a number of other satellites for many purposes, like military and communications; they also have a space station in orbit and have a number of space shuttles. Humanity has put a man on the moon, robots on mars and have a satellite that left the edge of the solar system in the 21st century, as well, becoming the first interstellar space craft built by man.

The 21st century brought a lot of things for man: the fastest type of engine so-far created, called the ion engine; cures for the major diseases that plagued the 20th century; the search for extraterrestrial life in our solar system (mainly observing Titan and Europa); and finally plans are currently being drawn up for the first human extraterrestrial base, for which planet identification technology has been created and artificial intelligence technology has begun to make leaping advancements.

Human Exploration
Several human civilizations have brought humanity far forward in exploration.

As humanity began in Africa, the colonisation of the rest of the world was a form of exploration, as humans superseded the dominant predators of the new regions and adapted using technology to unknown environments. The watercraft was a very important development, as it allowed cultures such as the Polynesians to travel far from their point of origin.

However, the cultures that predominated between the first cities and the renaissance did very little exploration. The Vikings and Chinese are important exceptions, and the Phoenicians circumnavigated Africa under the command of the Pharaohs. Trade existed between the Far East and Europe firstly through Persia and then through the Muslim Empire.

Starting from approximately the year 1500, the Portuguese, Dutch, Spanish, British and French nations began a rapid and ambitious program of exploration. They came across new cultures and continents, fostering trade links and creating colonies. However, soon afterwards a time of aggressive colonization began, and the competing European nations began to try and subdue flourishing civilizations such as the Benin, Aztecs and many more. The countries taking part were always trying to get the edge over the others, and wars between them were common. It was also about this time that devices such as the telescope and chronometer were developed.

Importantly, North America was settled at this time. Soon after its colonization, the War of Independence occurred. The United States emerged as a powerful country apart from Europe.

For the next few hundred years, the relative power of the British, French and Americans increased at the expense of other nations. The slave trade began, and people were displaced from their native countries to work elsewhere, usually in plantation run by European powers.

However, in the 20th century many colonies were granted independence, and soon very little of any empire was held. The World Wars, catastrophic for Europe, enabled the United States to become more powerful in comparison, due to its powerful industry and military. Aircraft appeared late in the 19th century, and allowed precise mapping and rapid travel around the world. The Soviet Union also gained power.

In 1957, the USSR launched its first space probe, Sputnik 1. This caused the Space Race between the USA and the USSR, which no other country could keep up with.

Yuri Gagarin was the first man in space, in 1961.

In 1969, the USA landed two men on the Moon.

In 1977, the furthest man-made object in space as of 2015, the Voyager 1, was launched.

According to the many-worlds interpretation theory, each and every outcome is in fact, real and possible, so there could be an alternate timeline or place where some other humanoid being have in fact, had contact with alien life, colonized a number of planets or even a few star systems.