Human| About Human| Knowledge About Human| NaturWild


Humans (Homo sapiens) are the most abundant and widespread species of primates, characterized by bipedality and large complex brains enabling the development of advanced tools, culture, and language. Humans are highly social beings and tend to live in large complex social structures composed of many cooperating and competing groups, from families and kinship networks to political states. Social interactions between humans have established a wide variety of values, social norms, and rituals, which bolster human society. Curiosity and the human desire to understand and influence the environment and to explain and manipulate phenomena have motivated humanity's development of science, philosophy, mythology, religion, and other fields of knowledge.

Humans evolved from other hominins in Africa several million years ago. Although some scientists equate humans with all members of the genus Homo, in common usage it generally refers to Homo sapiens, the only extant member. H. sapiens emerged around 300,000 years ago, evolving from Homo erectus and migrating out of Africa, gradually replacing local populations of archaic humans. Early humans were hunter-gatherers, before settling in the Fertile Crescent and other parts of the Old World. Access to food surpluses led to the formation of permanent human settlements and the domestication of animals. As populations became larger and denser, forms of governance developed within and between communities, and a number of civilizations rose and fell. Humans have continued to expand, with over 7.8 billion humans occupying almost all regions of the world in 2021.

Genes and the environment influence human biological variation in visible characteristics, physiology, disease susceptibility, mental abilities, body size, and life span. Though humans vary in many traits (such as genetic predispositions and physical features), two humans on average are over 99% similar, with the most genetically diverse populations from Africa. The greatest degree of genetic variation exists between males and females. On average, men have greater body strength and women generally have a higher body fat percentage. Females undergo menopause and become infertile decades before the end of their lives. They also have a longer life span in almost every population around the world. The division into male and female gender roles has varied historically, and challenges to predominant gender norms have recurred in many societies.

Humans are omnivorous, capable of consuming a wide variety of plant and animal material, and have used fire to prepare and cook food since the time of H. Erectus. They can survive for up to eight weeks without food and three or four days without water. Humans are generally diurnal, sleeping on average seven to nine hours per day. Childbirth is dangerous, with a high risk of complications and death. Both the mother and the father provide care for human offspring who are helpless at birth.

Humans have a large and highly developed prefrontal cortex, the region of the brain associated with higher cognition. They are intelligent beings, capable of episodic memory, flexible facial expressions, self-awareness, and a theory of mind. The human mind is capable of introspection, private thought, imagination, volition, and forming views on existence. This has allowed great technological advancements and complex tool development possible through reason and the transmission of knowledge to future generations. Language, art, and trade are defining characteristics of humans. Long-distance trade routes might have led to cultural explosions and resource distribution that gave humans an advantage over other similar species.

HISTORY

Until about 12,000 years ago, all humans lived as hunter-gatherers. The Neolithic Revolution (the invention of agriculture) first took place in Southwest Asia and spread through large parts of the Old World over the following millennia. It also occurred independently in Mesoamerica (about 6,000 years ago), China, Papua New Guinea, and the Sahel and West Savanna regions of Africa. Access to food surplus led to the formation of permanent human settlements, the domestication of animals, and the use of metal tools for the first time in history. Agriculture and sedentary lifestyle led to the emergence of early civilizations.

An urban revolution took place in the 4th millennium BCE with the development of city-states, particularly Sumerian cities located in Mesopotamia. It was in these cities that the earliest known form of writing, cuneiform script, appeared around 3000 BCE. Other major civilizations to develop around this time were Ancient Egypt and the Indus Valley Civilization. They eventually traded with each other and invented technology such as wheels, plops, and sails. Astronomy and mathematics were also developed and the Great The pyramid of Giza was built. There is evidence of a severe drought lasting about a hundred years that may have caused the decline of these civilizations, with new ones appearing in the aftermath. Babylonians came to dominate Mesopotamia while others, such as Poverty Point cultures, Minoans, and the Shang dynasty, rose to prominence in new areas. The bronze age suddenly collapsed about 1200 BCE resulting in the disappearance of a number of civilizations and the beginning of the Greek Dark Ages. During this period iron started replacing bronze leading to the Iron Age

In the 5th century, BCE history started being recorded as a discipline, so providing a much clearer picture of life at the time. Between the 8th and 6th century BCE Europe entered the classical antiquity age, a period when ancient Greece and ancient Rome flourished. Around this time other civilizations also came to prominence. The Maya civilization started to build cities and create complex calendars. In Africa, the Kingdom of Aksum overtook the declining Kingdom of Kush and facilitated trade between India and the Mediterranean. In West Asia, the Achaemenid Empire's system of centralized governance become the precursor to many later empires, while the Gupta Empire in India and the Han dynasty in China have been described as golden ages in their respective regions.

Following the fall of the Western Roman Empire in 476 Europe entered the Middle Ages. In the middle east, Islam became the prominent religion and expanded into North Africa. Christianity was likewise expanding in Europe, leading the Kingdom of England, the Kingdom of France, and the Holy Roman Empire to declare a series of holy wars to regain control of the Holy Land from Muslims. Elsewhere the Aztecs and Incas would become the dominant powers in the Americas and the Mongol Empire would conquer much of Eurasia in the 13th and 14th centuries. Over this same time period the Mali Empire in Africa grew to the largest empire in Africa, stretching from Senegambia to Ivory Coast.

Throughout the early modern period (1500–1800) the Ottomans controlled the lands around the Mediterranean Basin, Japan entered the Edo period, the Qing dynasty arose in China and the Mughal Empire ruled much of India. Europe underwent the Renaissance, starting in the 15th century and the Age of Discovery began with the exploring and colonizing of new regions. This includes the Scramble for Africa (where European control of Africa went from 10% to almost 90 in less than 50 years), the British Empire expanding to become the world's largest empire and the colonization of the Americas. This expansion led to the Atlantic slave trade and the genocide of Native American peoples. This period also marked the Scientific Revolution, with great advances in mathematics, mechanics, astronomy, and physiology.

The late modern period (1800–present) saw the Technological and Industrial Revolution bring such discoveries as imaging technology, major innovations in transport and energy development. The United States of America underwent a great change, going from a small group of colonies to one of the global superpowers. The Napoleonic Wars raged through Europe in the early 1800's, Spain lost most of its New World colonies and Europeans continued expansion into the islands of Oceania. A tenuous balance of power among European nations collapsed in 1914 with the outbreak of the First World War, one of the deadliest conflicts in history. In the 1930s, a worldwide economic crisis led to the rise of authoritarian regimes and a Second World War, involving almost all the world's countries. Following its conclusion in 1945, the Cold A war between the USSR and the United States saw a struggle for global influence, including a nuclear arms race and a space race. The current Information Age sees the world becoming increasingly globalized and interconnected.


Biology

Anatomy and physiology

Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology. The human body consists of the legs, the torso, the arms, the neck, and the head. An adult human body consists of about 100 trillion (1014) cells. The most commonly defined body systems in humans are the nervous, the cardiovascular, the digestive, the endocrine, the immune, the integumentary, the lymphatic, the musculoskeletal, the reproductive, the respiratory, and the urinary system. The dental formula of humans is 2.1.2.32.1.2.3. Humans have proportionately shorter palates and much smaller teeth than other primates. They are the only primates to have short, relatively flush canine teeth. Humans have characteristically crowded teeth, with gaps from lost teeth usually closing up quickly in young individuals. Humans are gradually losing their third molars, with some individuals having them congenitally absent.

Humans share with chimpanzees a vestigial tail, appendix, flexible shoulder joints, grasping fingers, and opposable thumbs. Apart from bipedalism and brain size, humans differ from chimpanzees mostly in smelling, hearing, and digesting proteins. While humans have a density of hair follicles comparable to other apes, it is predominately vellus hair, most of which is so short and wispy as to be practically invisible. Humans have about 2 million sweat glands spread over their entire bodies, many more than chimpanzees, whose sweat glands are scarce and are mainly located on the palm of the hand and on the soles of the feet.

It is estimated that the worldwide average height for an adult human male is about 171 cm (5 ft 7 in), while the worldwide average height for adult human females is about 159 cm (5 ft 3 in). Shrinkage of stature may begin in middle age in some individuals but tends to be typical in the extremely aged. Throughout history, human populations have universally become taller, probably as a consequence of better nutrition, healthcare, and living conditions. The average mass of an adult human is 59 kg (130 lb) for females and 77 kg (170 lb) for males. Like many other conditions, body weight and body type are influenced by both genetic susceptibility and environment and vary greatly among individuals.

Humans have a far faster and more accurate throw than other animals. Humans are also among the best long-distance runners in the animal kingdom, but slower over short distances. Humans' thinner body hair and more productive sweat glands help avoid heat exhaustion while running for long distances.

Genetics

Like most animals, humans are diploid eukaryotic species. Each somatic cell has two sets of 23 chromosomes, each set received from one parent; gametes have only one set of chromosomes, which is a mixture of the two parental sets. Among the 23 pairs of chromosomes, there are 22 pairs of autosomes and one pair of sex chromosomes. Like other mammals, humans have an XY sex-determination system, so that females have the sex chromosomes XX and males have XY. Genes and environment influence human biological variation in visible characteristics, physiology, disease susceptibility, and mental abilities. The exact influence of genes and environment on certain traits is not well understood.

While no humans—not even monozygotic twins—are genetically identical, two humans on average will have a genetic similarity of 99.5%-99.9%. This makes them more homogeneous than other great apes, including chimpanzees. This small variation in human DNA compared to other species suggests a population bottleneck during the Late Pleistocene (around 100,000 years ago), in which the human population was reduced to a small number of breeding pairs. The forces of natural selection have continued to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15,000 years.

The human genome was first sequenced in 2001 and by 2020 hundreds of thousands of genomes had been sequenced. In 2012 the International HapMap Project had compared the genomes of 1,184 individuals from 11 populations and identified 1.6 million single nucleotide polymorphisms. African populations also harbor the highest number of private genetic variants, or those not found in other places of the world. While many of the common variants found in populations outside of Africa are also found on the African continent, there are still large numbers that are private to these regions, especially Oceania and the Americas. By 2010 estimates, humans have approximately 22,000 genes. By comparing mitochondrial DNA, which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose genetic marker is found in all modern humans, the so-called mitochondrial Eve, must have lived around 90,000 to 200,000 years ago.



Life cycle

Most human reproduction takes place by internal fertilization via sexual intercourse, but can also occur through assisted reproductive technology procedures. The average gestation period is 38 weeks, but a normal pregnancy can vary by up to 37 days. Embryonic development in the human covers the first eight weeks of development; at the beginning of the ninth week, the embryo is termed a fetus. Humans are able to induce early labor or perform a cesarean section if the child needs to be born earlier for medical reasons. In developed countries, infants are typically 3–4 kg (7–9 lb) in weight and 47–53 cm (19–21 in) in height at birth. However, low birth weight is common in developing countries and contributes to the high levels of infant mortality in these regions.

Compared with other species, human childbirth is dangerous, with a much higher risk of complications and death. The size of the fetus's head is more closely matched to the pelvis than other primates. The reason for this is not completely understood, but it contributes to painful labor that can last 24 hours or more. 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.

Both the mother and the father provide care for human offspring, in contrast to other primates, where parental care is mostly restricted to mothers. Helpless at birth, humans continue to grow for some years, typically reaching sexual maturity at 15 to 17 years of age. The human life span has been split into various stages ranging from three to twelve. Common stages include infancy, childhood, adolescence, adulthood, and old age. The lengths of these stages have varied across cultures and time periods but are typified by an unusually rapid growth spurt during adolescence. Human females undergo menopause and become infertile decades before the end of their lives. It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring and in turn their children (the grandmother hypothesis), rather than by continuing to bear children into old age.

The life span of an individual depends on two major factors, genetics and lifestyle choices. For various reasons, including biological/genetic causes, women live on average about four years longer than men. As of 2018, the global average life expectancy at birth of a girl is estimated to be 74.9 years compared to 70.4 for a boy. There are significant geographical variations in human life expectancy, mostly correlated with economic development—for example, life expectancy at birth in Hong Kong is 87.6 years for girls and 81.8 for boys, while in Central African Republic, it is 55.0 years for girls and 50.6 for boys. The developed world is generally aging, with the median age around 40 years. In the developing world, the median age is between 15 and 20 years. While one in five Europeans is 60 years of age or older, only one in twenty Africans is 60 years of age or older. The number of centenarians (humans of age 100 years or older) in the world was estimated by the United Nations at 210,000 in 2002.