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As with all living species, humans share an ancestor with the first life on Earth, single celled organisms that existed about 4.54 billion years ago.

  • These ultimately gave rise to all the bacteria, fungi, plants, and animals (including humans) in existence today. However, the topic of human evolution usually begins with the evolutionary history of primates, who diverged from other mammals about 85 million years ago.
  • Humans share a last common ancestor with chimpanzees about 4-6 million years ago, at which point the line of human ancestors descended into various bipedal primate species, most prominently the australopithecines and later the genus Homo.
  • While genus Homo species moved out of Africa to live throughout Asia and Europe, fossil evidence suggests that modern Homo sapiens (modern humans) diverged from earlier species in Africa about 200,000 years ago.
  • This early fossil evidence of Homo sapiens is found exclusively in Africa, and so it supports the notion that modern humans originated on this particular continent.

Archaeologists and scientists have made, and continue to make, groundbreaking fossil discoveries that greatly increase our knowledge of the true origins of our species. Below is a timeline of some steps in the evolution of modern humans, including some of the most important discoveries that have made this knowledge possible.

1) Archicebus achilles (~55 million years ago)
The earliest primates are estimated to have diverged from other mammals about 85 million years ago.
  • Precious few fossils of the earliest primates exist, but in June of 2013 a team of paleontologists discovered a well-preserved fossilized skeleton of the very small shrew-like ancient species Archicebus achilles.
  • Found in what is now central China, this is the oldest currently known primate fossil at about 55 million years old. Species like this ultimately gave rise to all the modern primate species, including humans.

Lucy - Cleveland Natural History Museum
Lucy - Cleveland Natural History Museum

2) Australopithecines (2-4 million years ago)
The last common ancestor between modern chimpanzees and modern humans is estimated to have lived 4-6 million years ago.
  • Primate species on the human evolutionary line since this divergence with chimpanzees are called hominins. The now extinct genus Australopithecus contains some of the most prominent and well-known hominins. Australopithecines were among the first primates to display human-like bipedalism.

The genus Homo (whose name is taken from a Latin root meaning "man") eventually gave rise to modern humans (Homo sapiens). It is thought to have diverged from Australopithecusin Africa around 2 million years ago.
KNM ER 1813, a Homo habilis skull found in Kenya in 1974.
KNM ER 1813, a Homo habilis skull found in Kenya in 1974.


3) Homo habilis (2.2-1.4 million years ago)
Homo habilis is the oldest known species classified in the genus Homo.
  • It had larger cranial sizes than australopithecines, but still smaller than most other Homo species and much smaller than modern humans.
  • Its adult cranial capacity ranges from 550 to 687 cubic centimeters, while Australopithecus afarensis ranged from 380 to 430 cubic centimeters, and modern humans from 950 to 1800 cubic centimeters.
  • Some fossil finds have associated Homo habilis with stone tools, leading to speculation that they could have been the first true 'tool makers". KNM ER 1813, found in 1974 in Koobi Fora, Kenya, was a relatively complete Homo habilis skull estimated to be about 1.9 million years old.

4) Homo erectus and Homo ergaster (1.9-0.2 million years ago)
Homo ergaster and Homo erectus were later species of hominins who originally existed alongside but later replaced Homo habilis.
  • Classification of these hominins is extremely controversial, with some scientists arguing that they are distinct species and others saying Homo erectus is simply a later non-African version of Homo ergaster. Both species had larger cranial capacity than the earlier Homohabilis (700-1100 cubic centimeters), but smaller than modern humans.
  • With this additional brain capacity, they created various types of technology which enabled them to successfully survive in various different climates and terrains. Their more sophisticated technology and tools may have led to their eventual replacement of the earlier species.

The "Turkana Boy" fossil, found in near Lake Turkana of Kenya in 1984 by Kamoya Kimeu (member of a team led by Richard Leakey), is one of the most complete hominin fossils ever found.
  • It is a nearly full skeleton about 1.5 million years old, and classified today as a member of Homo ergaster.
  • It is thought to be an adult male skeleton, with an estimated height and weight of 6 feet 1 inch, 150 pounds.
  • Stone tools found along with the fossil helped suggest that Homo ergaster were hunters.

Click here for a trailer to "Bones of Turkana", a National Geographic special about this major fossil finding.

While Homo erectus is acknowledged to have first evolved in Africa, this species was highly adaptable in its technology and lifestyle, perhaps as a precursor to the later astounding adaptability of Homo sapiens.
  • Homo erectus fossils have been found in very different sites across the Eastern Hemisphere, including the Middle East, the Caucus Mountain region, modern-day China, and Java (an island in modern-day Indonesia). It is thought to be the first genus Homo species to leave Africa.
  • The "Peking Man" is a relatively modern Homo erectus fossil discovered near Beijing. It was identified by Davidson Black as Homo erectus by a single tooth.
  • Other excavations led to other skeletons being discovered in the same area. It is believed to be between 700,000 to 230,000 years old, making it close to the transition from Homo erectus to Homo sapiens. Read more here.
  • Theories as to how such a collection of Homo erectus bones and tools, as well as a large collection of animal remains, all came to reside in a single cave structure included the hypotheses of the practicing of cannibalism as well as the notion that these early humans were exceptional hunter gatherers. However, recent examination of the bones has introduced a new theory, that the "Peking Man" remains were the results of the feeding practices of a den of large hyena's. Read more here.

5) Homo sapiens (200,000 years ago to present)
Homo sapiens is the scientific name given to modern humans.
  • Sapiens comes from a Latin root meaning "wise" or "thinking". Homo sapiens is the only extant (not extinct, still living) species in the genus Homo. Its major immediate ancestor is thought to be Homo erectus, though it is thought to have first evolved only out of Homo erectus in Africa. It is thought that they existed alongside other genus Homo species for at least some time, though this is still controversial.
  • Among the oldest fossil finds of what are thought to be anatomically modern humans come from a number of excavated sites near the Omo River at Omo National Park in southwestern Ethiopia.
  • These bones were first found from 1967 to 1974 by a team led by Richard Leakey. They were first estimated to be about 130,000 years old, but later findings in 2005 suggested that they were actually about 195,00 years old, making them the oldest known examples of anatomically modern humans. The cranial capacity and pelvis shape were sufficiently different from examples of other Homo species that they were classified as Homo sapiens. This was tremendous support for the idea that anatomically modern humans first originated in Africa.