7 million years ago, Earth was almost the same as it is now. Africa was more humid and warm, but it was becoming drier. The tropics were thinning.
In these thinning forests lived Sahelanthropus tchadensis — the oldest known bipedal apes.
Brunet et al. A new hominid from the Upper Miocene of Chad, Central Africa
Other bipedal apes, Orrorin, are known from remains about 6 million years old. They also lived in forests and ate fruits.
Perhaps Sahelanthropus or Orrorin were the first representatives of the evolutionary branch that includes humans and their extinct ancestors.
Richmond, Jungers. Orrorin tugenensis. Femoral Morphology and the Evolution of Hominin Bipedalism
Little is known about Orrorin and Sahelanthropus: only individual bones have been found. Ardipithecus — apes that lived in East Africa 5.5–3.9 million years ago — is better studied.
Ardipithecus are the main candidates for the role of the “missing link” from ape to human. Their skeletons have many human-like features, but their brains are slightly smaller than those of modern chimpanzees.
Most fossil finds are younger than 4.5 million years. At this time, Australopithecus afarensis spread across Southeast Africa.
Early Australopithecus afarensis are studied from hundreds of fossils. Their pelvis and legs resemble ours, and they walked like humans: straightening their knees and stepping on their heels.
Judging by their hands, Australopithecus were not as adept at climbing trees as their ancestors. They lived in river valleys where savannas alternated with sparse forests.
Alemseged et al. A Juvenile Early Hominin Skeleton from Dikika, Ethiopia
About 2.5 million years ago a branch of Paranthropus — robust Australopithecus with powerful jaws — emerged. Paranthropus fed on grasses and seeds that are hard to chew.
Other Australopithecus did not need large jaws. Besides grass, they ate insects and carrion. Calorie-rich food helped their brains grow, and small jaws did not hinder skull expansion.
Wynn et al. Diet of Australopithecus afarensis from the Pliocene Hadar Formation, Ethiopia
While Paranthropus ate plants, their relatives switched to meat. Meat-eaters could not hunt but competed with hyenas for carcasses of ungulates.
To scrape meat from bones, they invented the stone chopper. The earliest tools are 2.5 million years old and could have been made by Australopithecus. But the first species to regularly use choppers was Homo habilis, the handy man.
The descendant of Homo habilis is Homo erectus, the upright man. They were taller, their brain was larger, and their legs were longer — like ours.
Homo erectus learned to act together. They solved difficult tasks together: taking prey from predators or even hunting. This allowed humans to obtain more meat to fuel their growing brains.
After the dispersal and evolution of Homo erectus, 800 thousand years ago, several human populations appeared in different parts of the world. They are collectively known as Homo heidelbergensis.
The brain of Homo heidelbergensis is comparable in size to ours. Its shape indicates improved motor control. They hunted with wooden spears and cooked over fire.
Homo heidelbergensis evolved independently in Europe and Africa. From the European population, 200 thousand years ago, a new advanced human species emerged — Neanderthals. Neanderthals are not our ancestors but a parallel branch of the evolutionary tree.
Judging by skull structure and genes, Neanderthals could speak. They wore clothes, used fire, cared for the elderly, and buried the dead — they were hardly less developed than early Homo sapiens.
Homo sapiens appeared in Africa. These are people with the same body and brain as ours, our direct ancestors. The oldest remains were found in southeastern Ethiopia, and they are 195 thousand years old.
46 thousand years ago Homo sapiens arrived in Europe. Soon the native inhabitants — Neanderthals — lost the competitive struggle and became extinct.
Leonid Vishnyatsky
Neanderthals. The history of an unfulfilled humanity
Stanislav Drobyshevsky
Non-Missing Link
Alexander Kozintsev
Origin and early history of Homo sapiens
Alexander Markov
Birth of Complexity,
Human Evolution
It is not possible to say definitively which Australopithecus humans evolved from.
When we say “lived this many years ago,” we mean the age of the bones. The dot • on the diagram indicates the age of the oldest (or only) find.
The age of finds is determined by the rock in which the fossils were found, neighboring fossils, and sophisticated methods like radiocarbon analysis.
Scientists judge the course of evolution by the structure of the skeleton, the location and the chemical composition of the find. Gray lines show relationships between spiecies.
All finds are assigned to a new or existing species. Often a species is described from fragments: Orrorin remains include a femur, shoulder, and seven teeth.
If lucky, scientists find individuals from different species of the same genus. Kadabba and ramidus are species of Ardipithecus.
The age of finds indicates when a genus arose and became extinct. These lifespans are marked on the diagram with white lines.
The boundaries between genera are conditional: humans are Australopithecus with a larger brain. Scientists often debate about what was found.
It is even more difficult with species. Some scientists distinguish three or four species of early humans. Others combine them all into one.
1.7 million years ago, humans first ventured into Eurasia. The skull above was found in Dmanisi, Georgia. It is the oldest find outside Africa.
People from Dmanisi are a transitional form from Homo habilis to Homo erectus. They have “modern” long legs but a small brain.
By this time, humans inhabited Southeast Asia, Africa, the Middle East, and Europe.
The genus Australopithecus evolved from Ardipithecus. That is, all Australopithecus had a common ancestor — Ardipithecus.
The descendants changed so much that they are classified as a separate genus.
Ardipithecus, Australopithecus, and early humans lived in southeast Africa.
Most finds are from the Great Rift Valley in Ethiopia.
People from the Indonesian island of Flores are an example of alternative evolution. In island isolation, their height decreased to a meter.
Multicellular life
1 billion years ago
Vertebrates
500 mya
Mammals
200 mya
Apes
60 mya
Anthropoids
25 mya
Sahelanthropus
7 mya
Ardipithecus
5.5 mya
Australopithecus
4.5 mya
First humans
2.3 mya
H. erectus
1.8 mya
H. heidelbergensis
800 kya
H. sapiens
200 kya
