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 beings 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 (probably due to convergent evolution), 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.

Constituents of the human body in a person weighing 60 kg
Constituent Weight Percentage of atoms
Oxygen 38.8 kg 25.5 %
Carbon 10.9 kg 9.5 %
Hydrogen 6.0 kg 63.0 %
Nitrogen 1.9 kg 1.4 %
Other 2.4 kg 0.6 %

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. In hybrids with other sapient species, this adaptability lessens or completely removes any inherited weaknesses.

Community content is available under CC-BY-SA unless otherwise noted.