Human

• 1. The First Two Million Years

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  In 2015, the United Nations estimated that there were 316,600 living centenarians worldwide. This number represents a tiny fraction of the global population yet highlights the incredible longevity some humans achieve. The species Homo sapiens emerged in Africa at least 300,000 years ago from a species commonly designated as either H. heidelbergensis or H. rhodesiensis. These early ancestors walked upright and possessed brains larger than those of their predecessors. Fossils like LD 350-1 from Ethiopia date back 2.8 million years and provide evidence of the earliest members of the genus Homo. The split between human and chimpanzee lineages occurred around 8 to 4 million years ago during the late Miocene epoch. During this divergence chromosome 2 formed from the joining of two other chromosomes leaving humans with only 23 pairs compared to 24 for other apes. Early hominins diversified into many species but all except one lineage are now extinct. The genus Homo evolved from Australopithecus though fossils from the transition remain scarce. Some studies estimate the Homo genus appeared 4.30 to 2.56 million years ago while others place it closer to 1.87 million years ago. H. erectus evolved 2 million years ago and was the first archaic human species to leave Africa and disperse across Eurasia. This species also developed a characteristically human body plan that allowed for long-distance travel and hunting.

• 2. The Great Migration Out

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  Migrating out of Africa, they gradually replaced and interbred with local populations of archaic humans. The out-of-Africa migration took place in at least two waves. The first wave occurred around 130,000 to 100,000 years ago while the second Southern Dispersal happened around 70,000 to 50,000 years ago. H. sapiens proceeded to colonize all continents and larger islands arriving in Eurasia 125,000 years ago. They reached Australia around 65,000 years ago and the Americas approximately 15,000 years ago. Remote islands such as Hawaii Easter Island Madagascar and New Zealand were settled between the years 300 and 1280 CE. Genomic research has shown that hybridization between substantially diverged lineages was common in human evolution. DNA evidence suggests several genes of Neanderthal origin are present among all non sub-Saharan African populations. Neanderthals and other hominins like Denisovans may have contributed up to 6% of their genome to present-day non sub-Saharan African humans. This genetic mixing allowed early humans to adapt quickly to new environments and survive diverse climates. The forces of natural selection continued to operate on human populations with evidence showing certain regions of the genome display directional selection in the past 15,000 years.

• 3. The Rise of Cities

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  Until about 12,000 years ago all humans lived as hunter-gatherers. The Neolithic Revolution 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. The formation of permanent human settlements domestication of animals and use of metal tools followed by permanent food surplus 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 development of city-states particularly Sumerian cities located in Mesopotamia. It was in these cities that earliest known form of writing cuneiform script appeared around 3000 BCE. Other major civilizations to develop around this time were Ancient Egypt and Indus Valley Civilisation. They eventually traded with each other and invented technology such as wheels plows and sails. Emerging by 3000 BCE Caral-Supe civilization is oldest complex civilization in Americas. Astronomy and mathematics were also developed and Great Pyramid of Giza was built. There is evidence of severe drought lasting about hundred years that may have caused decline of these civilizations with new ones appearing in aftermath.

• 4. The Genetic Blueprint

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  While no humans not even monozygotic twins are genetically identical two humans on average will have genetic similarity of 99.5% to 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 population bottleneck during Late Pleistocene around 100,000 years ago when human population reduced to small number of breeding pairs. The human genome was first sequenced in 2001 and by 2020 hundreds of thousands of genomes had been sequenced. In 2012 International HapMap Project had compared genomes of 1,184 individuals from 11 populations and identified 1.6 million single nucleotide polymorphisms. African populations harbor highest number of private genetic variants. While many common variants found in populations outside Africa are also found on African continent there are still large numbers that are private to these regions especially Oceania and Americas. By 2010 estimates humans have approximately 22,000 genes. By comparing mitochondrial DNA which is inherited only from mother geneticists concluded last female common ancestor whose genetic marker found in all modern humans so-called mitochondrial Eve must have lived around 90,000 to 200,000 years ago.

• 5. The Mind's Journey

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  Human consciousness at its simplest is sentience or awareness of internal or external existence. Despite centuries of analyses definitions explanations and debates by philosophers and scientists underlying nature of consciousness remains enigmatic and poorly understood being at once most familiar and most mysterious aspect of our lives. The only widely agreed notion about topic is intuition that it exists. Opinions differ about what exactly needs to be studied and explained as consciousness. Some philosophers divide consciousness into phenomenal consciousness which is sensory experience itself and access consciousness which can be used for reasoning or directly controlling actions. It is sometimes synonymous with mind and at other times an aspect of it. Historically it is associated with introspection private thought imagination and volition. It now often includes some kind of experience cognition feeling or perception. There might be different levels or orders of consciousness or different kinds of consciousness or just one kind with different features. The human brain perceives external world through senses and each individual human is influenced greatly by his or her experiences leading to subjective views of existence and passage of time.

• 6. Society and Structure

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  Humans are highly social with individual humans tending to belong to multi-layered network of distinct social groups from families and peer groups to corporations and political states. As such social interactions between humans have established wide variety of values social norms languages and traditions collectively termed institutions each of which bolsters human society. Human societies typically exhibit gender identities and gender roles that distinguish between masculine and feminine characteristics and prescribe range of acceptable behaviours and attitudes for their members based on sex. Most common categorisation is gender binary of men and women. Some societies recognize third gender or less commonly fourth or fifth. In some other societies non-binary is used as umbrella term for range of gender identities that are not solely male or female. Gender roles are often associated with division of norms practices dress behavior rights duties privileges status and power with men enjoying more rights and privileges than women in most societies both today and in past. All human societies organize recognize and classify types of social relationships based on relations between parents children and other descendants consanguinity and relations through marriage affinity.

• 7. The Eight Billion Mark

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  On the 15th of November 2022 the Day of Eight Billion marked a demographic milestone. As of 2026 there are estimated to be more than 8 billion living humans. It took over two million years of human prehistory and history for human population to reach one billion and only 207 years more to grow to 7 billion. The combined biomass of carbon of all 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. Most urbanized regions are Northern America 82% Latin America 81% Europe 74% and Oceania 68% with Africa and Asia having nearly 90% of 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. Human population growth industrialisation land development overconsumption and combustion of fossil fuels have led to environmental destruction and pollution that significantly contributes to ongoing mass extinction of other forms of life.