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What does “early hominin” mean?
A hominin is a member of the human lineage after it split from the lineage leading to living African apes. “Early hominins” therefore refers to multiple species across a long span of evolution, not one uniform type of creature or a single stage on the way to modern humans.
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Humans belong to the primate group, which also includes monkeys and apes. Our closest living relatives are other apes. Similarities between humans and living apes reflect shared ancestry, not descent from a chimpanzee, gorilla, or other living species. The Smithsonian National Museum of Natural History and the Smithsonian Institution Human Origins Program describe this branching relationship in their human-evolution resources.
How the groups compare
The table summarizes broad patterns, not rules that apply to every species or individual. “Other primates” includes highly varied monkeys and apes; “early hominins” includes many species with different combinations of traits.
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| Group | Locomotion and skeleton | Brain and skull | What the evidence can show |
|---|---|---|---|
| Modern humans | Habitual upright walking is characteristic. The Smithsonian describes a centrally positioned spinal opening and human hip anatomy among the clues to upright posture. | The Smithsonian gives an approximate average brain size of 1,300 cubic centimeters for modern humans. It describes the skull as thin-walled and high-vaulted, with a relatively flat, near-vertical forehead. | Living anatomy can be studied directly; fossils and archaeological traces help place modern humans in evolutionary context. |
| Early hominins | Evidence indicates a gradual transition toward regular upright walking, but anatomy and mobility varied by species. Not every early hominin had fully modern walking anatomy. | The Smithsonian says the earliest humans had brains similar in size to chimpanzees. That broad comparison does not specify every early hominin species or specimen. | Fossil bones, skulls, footprints, tools, and other traces provide different kinds of evidence; none alone reconstructs an entire way of life. |
| Other living primates | Monkeys and apes differ substantially from one another. Some occasionally walk on two legs, but occasional bipedal movement is not the same as habitual upright walking. | Brain and skull features vary among species. A single comparison cannot represent all non-human primates. | Researchers can observe living species directly, but living primates are not stand-ins for extinct hominins or direct ancestors. |
Why upright walking matters—and what fossils can tell us
Habitual bipedalism is one of the major features associated with the human lineage, but it did not appear in one sudden transformation. The Smithsonian Institution Human Origins Program describes fossil bones as recording a gradual shift from climbing toward regular upright walking. Some non-human primates also sometimes move on two legs, so seeing a primate stand or walk upright does not by itself establish habitual bipedalism.
Researchers assess posture and movement through multiple skeletal clues. The position of the opening where the spinal cord enters the skull, along with hip shape, can help indicate how an animal held and moved its body. These clues are interpreted in combination rather than treated as a single definitive test.
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Examples from particular fossils
- Orrorin tugenensis: The Smithsonian connects fossils assigned to this species with evidence suggesting upright walking. That evidence should not be taken as settling the exact timing or sequence of bipedal evolution.
- Homo erectus: The Smithsonian describes its hip as similar in size and broad shape to a modern human’s and interprets this as evidence that the species had given up climbing for walking. This is a species-specific interpretation, not a description of every early hominin.
How brains and skulls changed
Brains do not fossilize. Researchers instead examine the braincase—the part of the skull that enclosed the brain—and may use endocasts, natural or reconstructed replicas of its interior, to study aspects of brain shape. The Smithsonian Institution Human Origins Program notes that skulls and endocasts can provide evidence about brain size and form, but they do not reveal everything about an individual’s abilities or behavior.
The Smithsonian gives approximately 1,300 cubic centimeters as the average brain size of modern humans and says the earliest humans had brains similar in size to chimpanzees. The modern-human figure is an approximate average, not a measurement that applies to every person; the Smithsonian also notes variation between populations and sexes. The broad comparison with chimpanzees should not be mistaken for a precise figure for every early hominin species.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Modern human skulls are described by the Smithsonian as having a high vault with thin walls and a relatively flat, near-vertical forehead. Fossil skulls do not show that all these traits appeared together in a simple sequence. The Natural History Museum in London notes that fossils dating to approximately 300,000 years ago combine older features, such as a long braincase and strong brow ridge, with more modern traits, including a flatter face and thinner jawbones.
Why human evolution was a branching process
Human evolution is not a ladder in which one species simply turned into the next. Different hominin species lived at different times, and fossils can combine features that might once have seemed to belong to separate stages. Traits associated with humans emerged at different points rather than arriving as one complete package.
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The Natural History Museum says the origins of Homo sapiens cannot be traced to a single point in time. Its overview highlights fossils with mixed traits at approximately 300,000 years old, illustrating why modern-human origins are not adequately described as one uncontested birthplace and moment.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What fossils and artifacts reveal about behavior
Fossils can reveal aspects of anatomy and movement; tools, footprints, and other archaeological traces can provide evidence about behavior. The Smithsonian identifies changes in locomotion, diet, and behavior as subjects researchers investigate using human fossils and archaeological evidence. Its evidence overview describes thousands of human fossils and millions of artifacts and other traces available for study, without dating those counts.
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These records are partial. A tool can show that an object was made or used, for example, but does not by itself explain every detail of its maker’s daily life. Likewise, broad claims about diet or behavior should not be assigned to an entire hominin species unless species-specific evidence supports them. Archaeological traces help reconstruct the past, but they do not preserve a complete account of it.
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How to read claims about human origins
- Check which species is being discussed. A finding about Homo erectus is not automatically true of every early hominin.
- Separate evidence from interpretation. A fossil feature is observed; what it implies about posture, movement, or behavior is an interpretation based on several lines of evidence.
- Do not use brain size as a measure of intelligence. Braincase measurements are anatomical evidence, not a complete account of cognition.
- Keep living primates in perspective. They help researchers study primate variation, but they are not living ancestors or exact models of extinct species.
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