byzantine empire, and the rise of the ottoman empire. meanwhile, japan entered the edo period, the qing dynasty rose 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 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 great change, going from a small group of colonies to one of the global superpowers. the napoleonic wars raged through europe in the early 1800s, spain lost most of its colonies in the new world, while europeans continued expansion into africa – where european control went from 10% to almost 90% in less than 50 years – and 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 of the world's countries. following its conclusion in 1945, the cold 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. habitat and population population statistics 1,000+ million 200–1,000 million 100–200 million 75–100 million 50–75 million 25–50 million 10–25 million 5–10 million <5 millionworld population8 billionpopulation density16/km2 (41/sq mi) by total area54/km2 (139/sq mi) by land arealargest citiestokyo, delhi, shanghai, são paulo, mexico city, cairo, mumbai, beijing, dhaka, osaka, new york-newark, karachi, buenos aires, chongqing, istanbul, kolkata, manila, lagos, rio de janeiro, tianjin, kinshasa, guangzhou, los angeles-long beach-santa ana, moscow, shenzhen, lahore, bangalore, paris, jakarta, chennai, lima, bogota, bangkok, london early human settlements were dependent on proximity to water and – depending on the lifestyle – other natural resources used for subsistence, such as populations of animal prey for hunting and arable land for growing crops and grazing livestock. modern humans, however, have a great capacity for altering their habitats by means of technology, irrigation, urban planning, construction, deforestation and desertification. human settlements continue to be vulnerable to natural disasters, especially those placed in hazardous locations and with low quality of construction. grouping and deliberate habitat alteration is often done with the goals of providing protection, accumulating comforts or material wealth, expanding the available food, improving aesthetics, increasing knowledge or enhancing the exchange of resources. humans are one of the most adaptable species, despite having a low or narrow tolerance for many of the earth's extreme environments. through advanced tools, humans have been able to extend their tolerance to a wide variety of temperatures, humidity, and altitudes. as a result, humans are a cosmopolitan species found in almost all regions of the world, including tropical rainforest, arid desert, extremely cold arctic regions, and heavily polluted cities; in comparison, most other species are confined to a few geographical areas by their limited adaptability. the human population is not, however, uniformly distributed on the earth's surface, because the population density varies from one region to another, and large stretches of surface are almost completely uninhabited, like antarctica and vast swathes of the ocean. most humans (61%) live in asia; the remainder live in the americas (14%), africa (14%), europe (11%), and oceania (0.5%). within the last century, humans have explored challenging environments such as antarctica, the deep sea, and outer space. human habitation within these hostile environments is restrictive and expensive, typically limited in duration, and restricted to scientific, military, or industrial expeditions. humans have briefly visited the moon and made their presence felt on other celestial bodies through human-made robotic spacecraft. since the early 20th century, there has been continuous human presence in antarctica through research stations and, since 2000, in space through habitation on the international space station. humans and their domesticated animals represent 96% of all mammalian biomass on earth, whereas all wild mammals represent only 4%. estimates of the population at the time agriculture emerged in around 10,000 bc have ranged between 1 million and 15 million. around 50–60 million people lived in the combined eastern and western roman empire in the 4th century ad. bubonic plagues, first recorded in the 6th century ad, reduced the population by 50%, with the black death killing 75–200 million people in eurasia and north africa alone. human population is believed to have reached one billion in 1800. it has since then increased exponentially, reaching two billion in 1930 and three billion in 1960, four in 1975, five in 1987 and six billion in 1999. it passed seven billion in 2011 and passed eight billion in november 2022. it took over two million years of human prehistory and history for the human population to reach one billion and only 207 years more to grow to 7 billion. the combined biomass of the carbon of all the humans on earth in 2018 was estimated at 60 million tons, about 10 times larger than that of all non-domesticated mammals. in 2018, 4.2 billion humans (55%) lived in urban areas, up from 751 million in 1950. the most urbanized regions are northern america (82%), latin america (81%), europe (74%) and oceania (68%), with africa and asia having nearly 90% of the world's 3.4 billion rural population. problems for humans living in cities include various forms of pollution and crime, especially in inner city and suburban slums. humans have had a dramatic effect on the environment. they are apex predators, being rarely preyed upon by other species. human population growth, industrialization, land development, overconsumption and combustion of fossil fuels have led to environmental destruction and pollution that significantly contributes to the ongoing mass extinction of other forms of life. biology anatomy and physiology main article: human body basic anatomical features of female and male humans. these models have had body hair and male facial hair removed and head hair trimmed. the female model is wearing red nail polish on her toenails and a ring. 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 predominantly 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 varies 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 a graphical representation of the standard human karyotype, including both the female (xx) and male (xy) sex chromosomes (bottom right), as well as the mitochondrial genome (shown to scale as "mt" at bottom left). further information: karyotype like most animals, humans are a diploid and 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 many 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 harbor the highest number of private genetic variants. 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