Human

• 1. Introduction

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  Any two humans, picked at random from anywhere on Earth, share over 99% of their genetic code. Yet from that thin margin of difference comes everything: cuneiform pressed into clay, the Epic of Gilgamesh, footprints on the Moon. Humans, the species Homo sapiens, are the most abundant and widespread of all primates. They walk upright, carry almost no visible hair, and possess large, complex brains that build technology, language, and culture. In 2026, more than 8.3 billion of them occupy nearly every region of the planet. They are the first known species to send craft to other celestial bodies. How did a lineage that split from chimpanzees several million years ago come to cook with fire, cry emotional tears, and worship the divine? What separates the human animal from every other animal, when biologically it remains one? And why does a creature so genetically uniform vary so visibly across the globe? The answers lie in the brain, the body, and the long climb out of Africa.

• 2. Out Of Africa

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  The earliest record of the genus Homo is a 2.8 million-year-old specimen, LD 350-1, found in Ethiopia. Humans belong to the superfamily of apes, and their lineage split from gibbons first, then orangutans, then gorillas, and finally from chimpanzees and bonobos. That last split happened around 8 to 4 million years ago, in the late Miocene epoch. During it, two chromosomes fused into one, leaving humans with 23 pairs while other apes kept 24.

  Homo habilis and Homo rudolfensis evolved by 2.3 million years ago. Homo erectus appeared around 2 million years ago and became the first archaic human to leave Africa and spread across Eurasia. It was also the first to evolve a recognizably human body plan. Homo sapiens emerged in Africa at least 300,000 years ago, descended from a species often called H. heidelbergensis or H. rhodesiensis.

  The migration out of Africa came in waves, the first around 130,000 to 100,000 years ago, the second around 70,000 to 50,000 years ago. Humans reached Eurasia 125,000 years ago, Australia around 65,000 years ago, and the Americas around 15,000 years ago. Remote places like Hawaii, Easter Island, Madagascar, and New Zealand were settled between 300 and 1280 CE.

  The journey was not a clean branching tree. Genomic research shows that hybridization between diverged lineages was common, and Neanderthals and Denisovans may have contributed up to 6% of the genome of present-day non sub-Saharan-African humans. The DNA of vanished cousins still rides inside billions of living people.

• 3. The Genetic Margin

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  In 1984, the US government began planning the human genome project, which officially started in 1990 and reached completion in April 2003. By 2010 estimates, humans carry roughly 22,000 genes. The small variation in human DNA points to a population bottleneck during the Late Pleistocene, around 100,000 years ago, when the breeding population shrank to a small number.

  No two humans are genetically identical, not even monozygotic twins, yet any two people share between 99.5% and 99.9% of their DNA. This makes the species more homogeneous than chimpanzees. Sex determination runs primarily through the SRY gene on the Y chromosome, and the protein it expresses, not the chromosomes alone, initiates male gonadal differentiation.

  African populations are the most genetically diverse, and diversity decreases with migratory distance from the continent. West African populations carry ancestral variation that predates modern humans and has been lost elsewhere, some of it thought to come from an unknown archaic hominin. By comparing mitochondrial DNA, passed only from mother to child, geneticists trace a last common female ancestor, the so-called mitochondrial Eve, who lived around 90,000 to 200,000 years ago. Natural selection has not stopped working. Certain regions of the genome show directional selection within the past 15,000 years.

• 4. A Visible Spectrum

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  Skin color in humans ranges from the darkest brown to the lightest peach, and nearly colorless in cases of albinism. It varies clinally and tracks ultraviolet radiation, with darker skin clustered around the equator. Darkening likely evolved as protection against solar radiation, while lighter pigmentation guards against the depletion of vitamin D, which needs sunlight to form.

  The genes that let adults digest lactose run at high frequency in populations with long histories of cattle domestication. Sickle cell anemia, which can resist malaria, is common where malaria is endemic. Populations long settled in cold regions tend toward short, stocky builds, while those in hot regions run tall and lanky. The Bajau, an ocean-dwelling people, evolved adaptations suited to freediving.

  The sharpest genetic divide is not between continents but between the sexes. The nucleotide variation between individuals of the same sex stays under 0.1% to 0.5%, while the difference between males and females runs between 1% and 2%. Males average 15% heavier and 15 cm taller, with 40 to 50% more upper-body strength. Females carry a higher body fat percentage, undergo menopause around age 50, and outlive males in almost every population on Earth. Two people from the same population group are almost as different from each other as two people from any two different groups.

• 5. The Helpless Newborn

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  Human childbirth is dangerous in a way that sets the species apart. The fetus's head is matched more tightly to the pelvis than in other primates, which can stretch labor to 24 hours or more. In developing regions, maternal death rates run roughly 100 times higher than in developed countries. The average gestation period is 38 weeks, and in developed countries infants weigh 3 to 4 kg and measure 47 to 53 cm at birth.

  Unlike most primates, where the mother does nearly all the work, both parents care for human offspring. Children are helpless at birth and keep growing for years, reaching sexual maturity at 15 to 17. Menopause may carry a hidden advantage. The grandmother hypothesis proposes that by stopping reproduction, a woman can pour resources into existing children and their children rather than bearing more.

  Lifespan turns on genetics and lifestyle, and on geography. The global average life expectancy at birth is estimated at 74.9 years for a girl and 70.4 for a boy. In Hong Kong those figures reach 87.6 and 81.8 years, while in the Central African Republic they fall to 55.0 and 50.6. The developed world is aging, with a median age near 40, while in the developing world it sits between 15 and 20. In 2012, the United Nations counted 316,600 living centenarians worldwide.

• 6. The Singular Mind

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  Humans are the only animals known to cry emotional tears. They carry a larger and more developed prefrontal cortex than other primates, the region tied to higher cognition, which has led the species to declare itself the most intelligent. They may be the only animals with episodic memory and the ability to engage in mental time travel. Even among social animals, their facial expressions show unusual flexibility.

  Consciousness remains the puzzle at the center. Described as at once the most familiar and most mysterious aspect of our lives, its nature stays poorly understood after centuries of debate. Some philosophers split it into phenomenal consciousness, the raw feel of sensory experience, and access consciousness, used for reasoning and controlling action.

• 7. Fire, Tools, And Trade

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  Stone tools were used by proto-humans at least 2.5 million years ago, and the manufacture of tools has been called the ability that defines humans more than any other. Controlled use of fire began around 1 million years ago. The wheel and wheeled vehicles appeared in several regions during the fourth millennium BC. China later developed paper, the printing press, gunpowder, and the compass.

  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 arose independently in Mesoamerica, China, Papua New Guinea, and parts of Africa. Domestication of wild plants began about 11,700 years ago. The spread of dairy farming even reshaped human biology, selecting for the ability to digest lactose into adulthood.

  Trade is cited as a practice that gave Homo sapiens a major edge over other hominids. Early humans used long-distance routes to exchange goods like obsidian, networks the Neanderthals lacked. Early money took the form of commodities, the oldest being cattle and the most widely used being cowrie shells. The inequalities that followed are staggering. The eight richest humans are worth the same monetary value as the poorest half of all humanity.

• 8. Belief, Beauty, And War

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  The earliest evidence of art is shell engravings made by Homo erectus 300,000 years before modern humans evolved. Art attributed to H. sapiens dates back at least 75,000 years, with jewelry and drawings found in caves in South Africa. One of the oldest surviving works of literature, the Epic of Gilgamesh, was first engraved on Babylonian tablets about 4,000 years ago. Music predates cave art and has been practiced by virtually every known culture, with brains synchronizing to rhythm in a process called entrainment.

  Language is unique to humans and stands as a cultural universal. It is open, able to generate an infinite number of meanings from a limited set of symbols, and it carries displacement, the power to speak of things not present. Humans used roughly six thousand different languages, including sign languages, with many thousands more extinct.

  Religious behavior shows credible evidence from the Middle Paleolithic, between 45,000 and 200,000 years ago. As of 2015, the plurality of humans were Christian, followed by Muslims, Hindus, and Buddhists, while about 16%, slightly under 1.2 billion people, were irreligious.

  Violence has shadowed the species throughout. Phylogenetic analysis predicts that 2% of early H. sapiens would be murdered, rising to 12% in the medieval period, then dropping below 2% in modern times. During the 20th century, between 167 million and 188 million people died as a result of war. Yet the years since 1945 have seen a very significant drop in death rates from armed conflict, the steepest in 600 years.