Human facts: Humans differ in skin color, depending on the amount of the pigment melanin in their skin. The body is hairless, except for the head, armpits, and genital areas. Scientists suggest that early humans had shed their fur to prevent over-heating when chasing their prey, and developed sweat glands on the skin surface to cool the body by perspiring. The subcutaneous fat, or the fatty layer under the skin, preserves body heat when the environment gets cold and serves as an energy source when food is scarce.
Humans possess a distinct trait, bipedalism (bye-PED-ul-ih-zem), or a mode of locomotion on two legs. Strong, muscular legs are adapted for upright walking. The S-shaped curve of the spine keeps an erect human from toppling by distributing the body weight to the lower back and hips. However, the flexible spine, adapted by early humans for running and catching prey, has caused problems to modern humans, especially the weak lower backbone that is not adapted for supporting the heavy head and trunk.
Geographic range: Humans inhabit almost all of Earth’s land surfaces. While humans may not be able to live in the very cold regions of Antarctica or in the central Sahara Desert, they are capable of visiting those areas. Modern technology has allowed humans to travel over water, underwater, and through the air. Humans are also able to live in space, such as in the International Space Station, and have landed on the moon.
Human habitat: Humans live in all land habitats.
What does human eat: Humans are omnivorous, feeding on both plant and animal matter.
Behavior and reproduction: Humans differ from other primates by their use of language, a distinct type of communication that can be manipulated to produce an unlimited number of expressions. Humans use symbols and communicate through symbols, such as art. Another human-specific behavior is their reliance on tools and technology. However, humans’ most striking characteristic is their mental ability to create ideas.
Although a monogamous (muh-NAH-guh-mus) family, with a mated male and female, typically represents the human social unit, many cultures practice polygyny (puh-LIH-juh-nee; one male with several mates), polyandry (PAH-lee-an-dree; one female with several mates), and polygamy (puh-LIH-guh-mee; both sexes have several mates). Humans are unique in that they do not generally sever ties with relatives when they move. However, humans are capable of aggressive and violent relationships.
Humans have no breeding seasons. While single births are most common, multiple births occasionally occur. Human young develop slowly, needing care and protection from adults. The young learn social behaviors through imitation. While average life spans can vary around the world, men and women generally live into their sixties and seventies. While males can parent children in old age, females stop reproducing with menopause (generally starting at age fifty), after which they may live many more years.
According to scientists, the human baby, given the big size of its brain, needs about twenty-one months to develop fully in the mother’s womb. But, since the female birth canal, through which a baby passes, has evolved to a narrower size to allow for upright locomotion, babies have to be born “prematurely” (after nine months). The brain develops further outside the womb.