Humans are a tetrapodal species from the planet Earth. They use their hind two limbs for walking and their front two limbs for manipulating objects; though note, ‘hind’ and ‘front’ is misleading, because their torso is entirely vertical and as such their front limbs are positioned above their back limbs. They have a soft, fleshy nose and ears, with extra tissue and cavities in each to help with smell and hearing. They have sparse hair on their bodies, except for a dense growth on top of their heads. Oddly, they have no snout, and their eyes are positioned directly above their nose and mouth. They have five digits on each of their hands and feet, and they walk plantigrade, with both their toes and feet on the ground.
Modern humans are classified as Homo sapiens. Their closest living relatives are chimpanzees, and they evolved most of their giveaway features only in the last few million years.
At some point before 4 million years ago, they evolved to be bipedal, possibly so they could carry fruits in their arms and walk around at the same time. Later, they would evolve smaller jaws and bigger braincases so that they could better support their increasing levels of intelligence.
This sapience might have been brought on by the transition to cooking their food, which is much more nutritious than simply eating it raw. It allowed them to craft tools like spears and arrows, which facilitated their dominion over other animals, even in the Palaeolithic.
Though ancient human species travelled out from their home continent several times before H. sapiens, modern humans would eventually start migrating across the world less than 100,000 years ago, facilitating the extinction of their many cousins and becoming present on almost every ecosystem on Earth.
Though they do not resemble most mammals, humans still have some features that give away their evolutionary origin. They do not lay eggs, instead keeping their young inside a specialised organ called a uterus where it develops. However, unlike most animals, humans are not born fully developed- they require several years to learn to walk and communicate properly.
Before their teeth come in, they are naturally fed a nutrient-containing liquid produced in specialised ducts found in most human women. This milk can be siphoned by the infant directly from the milk ducts through a special fleshy tap called a nipple.
Humans are omnivores, but they are one of the most herbivorous sapient species known. Most of their diet consists of fruits, vegetables, nuts, and grains- the grains often baked in creative ways, like bread.
They also eat protein from a wide range of sources, including meat, fish, eggs, milk, arthropods, and meat cultures. Herbs and sometimes minerals are used to season food. Sweet delicacies are made from heavily processed foods like butter, raw sugar, and chocolate. Because they have evolved to be so heavily omnivorous, humans can consume otherwise poisonous substances like caffeine, theobromine, alcohol, and high amounts of sugar.
Inside their neck, at the top of their windpipe, humans have a structure called the larynx. Air passing through their windpipe and into their larynx produces sounds for speech. However, the larynx is not very versatile, and only controls the pitch of someone’s voice. Many of the different sounds humans make are a result of their mouth moving to regulate airflow; for example, sounds like ‘m’ are made with a closed mouth, and sounds like ‘d’ are made as simultaneously air flows through the mouth and the tongue touches the roof of the mouth.
Humans have no patterns on them; apart from rare cases, their skin is entirely one colour, hair is another colour, and eyes are another. However, given their diverse geographical range on their home planet, they come in a variety of pigments, which have evolved to either reflect or absorb sunlight. Skin ranges from dark brown to light pink, hair from white-gold to deep black, and eyes from pale blue to dark brown. These characteristics tend to co-occur in complexions which have been called races.
Humans are one of the least sexually dimorphic sapient species known. Apart from their sex organs, most mature women have milk-producing organs called breasts, and some men will grow extra hair around their mouth.
Humans seem to be naturally monogamous, with most of them forming romantic partnerships with one other person for anywhere from a few months to a lifetime. This is often ingrained in human culture. Some, though, are polyamorous, and some do not seek romance.
Regardless, human women sometimes find themselves in possession of a developing foetus. This foetus will spend nine months in the womb before live birth occurs, though it is still not done developing. Human children need three or four years to develop until the point that most animals are when they are born. In this time, their body grows to better match the proportion of their head, and they become able to walk and talk.
After this, they will grow for another fifteen to twenty years before they become full adults. Finally, when they are fifty to sixty years old, their health starts to decline and they enter old age. On Mars, humans have an average lifespan of 97 years.