Humans (Homo sapiens) are primates of the family Hominidae, and the only extant species of the genus Homo. They originated in Africa, where they reached anatomical modernity about 200,000 years ago and began to exhibit full behavioral modernity around 50,000 years ago.
Human body types vary substantially. Although body size is largely determined by genes, it is also significantly influenced by environmental factors such as diet and exercise. The average height of an adult human is 1.4 m to 1.9 m tall, although this varies significantly from place to place and depending on ethnic origin. The average mass of an adult human is 54–64 kg for females and 76–83 kg for males. Weight can also vary greatly (e.g. obesity).
Although humans appear hairless compared to other primates, with notable hair growth occurring chiefly on the top of the head, underarms and pubic area, the average human has more hair follicles on his or her body than the average chimpanzee. The main distinction is that human hairs are shorter, finer, and less heavily pigmented than the average chimpanzee's, thus making them harder to see. Humans, like other primates, have sweat glands, better enabling them to conserve energy in tropical environments.
The hue of human skin and hair is determined by the presence of pigments called melanins. Human skin hues can range from dark brown to pale pink, or even nearly white or colorless, such as in cases of Albinism. Human hair ranges from white to brown to red to most commonly black. This depends on the amount of melanin (an effective sun blocking pigment) in the skin and hair, with hair melanin concentrations in hair fading with increased age, leading to grey or even white hair. The skin pigmentation of contemporary humans is clinally distributed across the planet, and in general correlates with the level of ultraviolet radiation. Human skin also has a capacity to darken in response to exposure to ultraviolet radiation.
The construction of the human pelvis differs from other primates, as do the toes. As a result, humans are slower for short distances than most other animals, but are among the best long-distance runners in the animal kingdom. Humans' thinner body hair and more productive sweat glands also help avoid heat exhaustion while running for long distances. A trade-off for these advantages of the modern human pelvis is that childbirth is more difficult and dangerous, especially given that the larger head size of human babies compared to other primates. This means that human babies must turn around as they pass through the birth canal which other primates do not do, and it makes humans the only species in which females require help from their conspecifics to reduce the risks of birthing.
Humans are uniquely adept at utilizing systems of symbolic communication such as language for self-expression, the exchange of ideas, and organization. Humans create complex social structures composed of many cooperating and competing groups, from families and kinship networks to states. Social interactions between humans have established an extremely wide variety of values, social norms, and rituals, which together form the basis of human society. Humans are noted for their desire to understand and influence their environment, seeking to explain and manipulate phenomena through science, philosophy, mythology, and religion.
As with other mammals, human reproduction takes place as internal fertilization by sexual intercourse.
The zygote divides inside the female's uterus to become an embryo, which over a period of 38 weeks (9 months) of gestation becomes a fetus. After this span of time, the fully grown fetus is birthed from the woman's body and breathes independently as an infant for the first time. At this point, most modern cultures recognize the baby as a person entitled to the full protection of the law, though some jurisdictions extend various levels of personhood earlier to human fetuses while they remain in the uterus.
Compared with other species, human childbirth is dangerous. Painful labors lasting 24 hours or more are not uncommon and sometimes lead to the death of the mother, the child or both. This is because of both the relatively large fetal head circumference and the mother's relatively narrow pelvis. The chances of a successful labor increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and natural childbirth remain hazardous ordeals in developing regions of the world, with maternal death rates approximately 100 times greater than in developed countries.
Helpless at birth, humans continue to grow for some years, typically reaching sexual maturity at 12 to 15 years of age. Females continue to develop physically until around the age of 18, whereas male development continues until around age 21. The human life span can be split into a number of stages: infancy, childhood, adolescence, young adulthood, adulthood and old age. Compared to other primates, humans experience an unusually rapid growth spurt during adolescence, where the body grows 25% in size.
The presence of the growth spurt is probably necessary to keep children physically small until they are psychologically mature. Humans are one of the few species in which females undergo menopause.
Humans are omnivorous, capable of consuming a wide variety of plant and animal material. Varying with available food sources in regions of habitation, and also varying with cultural and religious norms, human groups have adopted a range of diets, from purely vegetarian to primarily carnivorous. In some cases, dietary restrictions in humans can lead to deficiency diseases. The human diet is prominently reflected in human culture, and has led to the development of food science.
Until the development of agriculture approximately 10,000 years ago, Homo sapiens employed a hunter-gatherer method as their sole means of food collection. This involved combining stationary food sources (such as fruits, grains, tubers, and mushrooms, insect larvae and aquatic mollusks) with wild game, which must be hunted and killed in order to be consumed. Around ten thousand years ago, humans developed agriculture, which substantially altered their diet.
In general, humans can survive for two to eight weeks without food, depending on stored body fat. Survival without water is usually limited to three or four days. About 36 million humans die every year from causes directly or indirectly related to hunger.
Humans are highly social beings and tend to live in large complex social groups. More than any other creature, humans are adept at utilizing systems of communication for self-expression, the exchange of ideas, and organization, and as such have created complex social structures composed of many cooperating and competing groups. Human groups range from families to nations. Social interactions between humans have established an extremely wide variety of values, social norms, and rituals, which together form the basis of human society.
Culture is defined here as patterns of complex symbolic behavior, i.e. all behavior that is not innate but which has to be learned through social interaction with others.
All human societies organize, recognize and classify types of social relationships based on relations between parents and children (consanguinity), and relations through marriage (affinity). These kinds of relations are generally called kinship relations. In most societies kinship places mutual responsibilities and expectations of solidarity on the individuals that are so related, and those who recognize each other as kinsmen come to form networks through which other social institutions can be regulated. In many societies kinship relations can also be formed through forms of co-habitation, adoption, fostering, or companionship, which also tends to create relations of enduring solidarity.
Tools and Technology
Stone tools were used by proto-humans at least 2.5 million years ago. The controlled use of fire began around 1.5 million years ago. Since then, humans have made major advances, developing complex technology to create tools to aid their lives and allowing for other advancements in culture. Major leaps in technology include the discovery of agriculture – what is known as the Neolithic Revolution, and the invention of automated machines in the Industrial Revolution.
Throughout their history humans have altered their appearance by wearing clothing and adornments, by trimming or shaving hair or by means of body modifications.
Body modification is the deliberate altering of the human body for any non-medical reason, such as aesthetics, sexual enhancement, a rite of passage, religious reasons, to display group membership or affiliation, to create body art, shock value, or self-expression. In its most broad definition it includes plastic surgery, socially acceptable decoration (e.g., common ear piercing in many societies), and religious rites of passage (e.g., circumcision in a number of cultures).