Human Evolution Timeline

The possibility of linking humans with earlier apes by descent became clear only after 1859 with the publication of Charles Darwin's On the Origin of Species, in which he argued for the idea of the evolution of new species from earlier ones.

Image source: On the Origin of Species

Thomas Huxley argued for human evolution from apes by illustrating many of the similarities and differences between humans and other apes in his 1863 book Evidence as to Man's Place in Nature.

Image source: Man's Place in Nature

A major problem in the 19th century was the lack of fossil intermediaries. Despite early Neanderthal finds and Dubois' Java Man, it was only in the 1920s when such fossils were discovered in Africa that intermediate species began to accumulate.

Darwin applied the theory of evolution and sexual selection to humans in his 1871 book The Descent of Man, and Selection in Relation to Sex, extending his evolutionary framework to humanity itself.

Image source: The Descent of Man, and Selection in Relation to Sex

Franz Weidenreich compared in detail the characters of Dubois' Java Man, then named Pithecanthropus erectus, with Peking Man, then named Sinanthropus pekinensis. He concluded in 1940 that because of their anatomical similarity with modern humans, all these specimens should be gathered in a single species of the genus Homo.

This model was proposed in 1988 by Milford H. Wolpoff, suggesting that modern humans evolved across multiple regions of the Old World with gene flow between populations, in contrast to recent African origin models.

Image source: Multiregional origin of modern humans

In 1994, Randall Susman used the anatomy of opposable thumbs as the basis for his argument that both the Homo and Paranthropus species were toolmakers, expanding views on which hominins manufactured stone tools.

Image source: Paranthropus

A 2007 study provides support for the hypothesis that bipedalism evolved because it used less energy than quadrupedal knuckle-walking, offering an adaptive explanation for one of humanity's defining traits.

Image source: Bipedalism

Encephalization has been tied to increased starches and meat in the diet; however, a 2022 meta study called into question the role of meat in driving the evolution of larger brains in the human lineage.

In May 2023, scientists reported a more complicated pathway of human evolution than previously understood, reflecting discoveries since 2010 showing that human evolution should not be seen as a simple linear or branched progression, but a mix of related species.

In 1925, Raymond Dart described Australopithecus africanus, one of the first hominin species recognized from Africa, helping to establish Africa as a key region for understanding human origins.

Image source: Australopithecus africanus

In 1994, Meave Leakey discovered Australopithecus anamensis, an early bipedal hominin species that extended knowledge of the earliest stages of human evolution in East Africa.

Image source: Australopithecus anamensis

White's 1995 discovery of Ardipithecus ramidus pushed back the fossil record to 4.2 million years ago, revealing an earlier stage of hominin evolution closer to the human-chimpanzee split.

Image source: Ardipithecus ramidus

In 2000, Martin Pickford and Brigitte Senut discovered, in the Tugen Hills of Kenya, a 6-million-year-old bipedal hominin which they named Orrorin tugenensis, among the oldest known potential human ancestors.

Image source: Orrorin

In 2001, a team led by Michel Brunet discovered the skull of Sahelanthropus tchadensis, dated to 7.2 million years ago, which Brunet argued was a bipedal hominin, pushing back the possible origin of the human lineage.

Image source: Sahelanthropus

Found in 2003 and dated to approximately 18,000 years old, this small-bodied hominin from Flores, Indonesia, had a brain size far below the modern Homo sapiens average of 1400 cm3, demonstrating surprising diversity in late-surviving human relatives.

Image source: Homo floresiensis

In 2010, Saadanius was described as a close relative of the last common ancestor of the crown catarrhines, tentatively dated to 29–28 million years ago, helping to fill an 11-million-year gap in the fossil record.

Image source: Saadanius

In May 2010, a new species, Homo gautengensis, was proposed based on specimens discovered in South Africa, adding to the growing diversity of recognized species within the genus Homo.

Image source: Homo gautengensis

In 2013, fossil skeletons of Homo naledi, an extinct species of hominin provisionally assigned to the genus Homo, were found in the Rising Star Cave system in South Africa's Cradle of Humankind region near Johannesburg. As of September 2015, fossils of at least fifteen individuals, amounting to 1,550 specimens, had been excavated.

Image source: Homo naledi

In their seminal 1967 paper in Science, Sarich and Wilson estimated the divergence time of humans and apes as four to five million years ago, at a time when standard interpretations of the fossil record gave this divergence as at least 10 to as much as 30 million years.

Patterson (2006) dated the final divergence between humans and chimpanzees at 5 to 6 million years ago, refining estimates of when the two lineages separated.

Sequencing of the Neanderthal genome in 2010 indicated that Neanderthals did indeed interbreed with anatomically modern humans during the Middle Paleolithic and early Upper Paleolithic, confirming long-debated hybridization between human species.

Image source: Neanderthal genetics

A 2012 study in Iceland of 78 children and their parents suggests a mutation rate of only 36 mutations per generation; this datum extends the separation between humans and chimpanzees to an earlier period greater than 7 million years ago.

Sergi Castellano of the Max Planck Institute reported in 2016 that while Denisovan and Neanderthal genomes are more related to each other than to ours, Siberian Neanderthal genomes show more similarity to modern human genes than do European Neanderthal populations.

Image source: Interbreeding between archaic and modern humans

In a 2016 comparative genomics study, a Harvard Medical School/UCLA research team made a world map of the distribution of Denisovan and Neanderthal genes and made predictions about where they may be impacting modern human biology.

A 2023 genetic study suggests that a similar human population bottleneck of between 1,000 and 100,000 survivors occurred around 930,000 and 813,000 years ago, indicating a dramatic reduction in ancestral human population size.

Image source: Population bottleneck