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Humans, extinct Homo-species
All bipedal ancestors

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Homo Ergaster one of many hominins involved in Human Evolution
Hominins, like this reconstruction of Homo Ergaster, form the collective base for modern humans. Image by Werner Ustorf. (CC BY-SA 2.0)

What Are Hominins?

The term 'hominin' - first introduced in 1948, by the French paleontologist Camille Arambourg (1885–1969) - refers to a loose evolutionary group of human and pre-human species, which includes:


Historically, the term 'hominid' was used to describe all modern and extinct great apes, including chimpanzees, gorillas, orang-utans and humans, as well as all their immediate ancestors.

However, with advances in paleontology and molecular biology, taxonomical classifications were refined.

As a result, we have a new category of 'Hominin'. This category is much narrower than the traditional 'hominid' category, as it excludes chimpanzees, gorillas, orang-utans and any other pre-homo species that did not walk upright.

Who Were the Earliest Hominins?

The earliest hominins were considered to be Sahelanthropus tchadensis who lived in north-central Africa around Chad between 7 and 6 million years ago, and Orrorin tugenensis who lived in central Kenya between 6.2 and 5.8 million years ago.

This is because the hominin lineage diverged from the line leading to chimpanzees and bonobos between 7 and 6 million years ago.

Another early hominin was Ardipithecus ramidus, from the Afar region of Early Pliocene Ethiopia.

However, all three species spent much of their time in the trees, suggesting they were probably largely arboreal species who walked bipedally whenever they came down to the ground.

As a result, some experts now think either that these species were likely not early hominins or, alternatively, that the earliest hominins had not yet adapted to walking on two legs.

Around 4.5 million years ago, we encounter the genus Australopithecus (the name means 'southern ape'), who lived in East and South Africa between 4.5 and 2 million years ago.

Australopiths are seen as the intermediate species between the earliest hominins and the genus Homo.

The most famous Australopithecus species are A. afarensis, who lived in East Africa between 3.9 and 2.9 million years ago, and A. africanus, who lived in Southern Africa between 3.3 and 2 million years ago.

Their anatomy confirms they were fully bipedal but, compared to Homo sapiens, their forearms, fingers and toes were long and a little curved, implying that Australopiths continued to use the trees for food and protection.

How are Hominin Fossils Dated?

By using a combination of relative and absolute dating technologies. For details, see: Dating Methods in Archaeology.

First Human Hominin

The late australopithecines were already walking upright (bipedal), and were beginning to exhibit changes in skull, brain, jaw and teeth that were more characteristic of modern humans.

Thus many paleoanthropologists believe that the genus Homo emerged in Africa somewhere within these late Australopiths.

However, there is no consensus on exactly which species of Australopithecus evolved into the Homo line.

A. garhi was originally thought to be a direct ancestor of Homo and the human line, but is now believed to have been an offshoot.

It has also proved very difficult to determine which hominin constitutes the first member of the genus Homo. But until we identify this human species, it is not possible to determine its australopithecine ancestor.

Evolution of Hominins

The evolution of hominins is marked by a number of anatomical modifications, which improved their skills as hunter-gatherers and thus their ability to compete for resources.


This is perhaps the most defining trait of hominins. Bipedal adaptations freed the hands and allowed the use of tools, a transformative development in hominin evolution.

Early evidence of this adaptation is visible in species like Ardipithecus ramidus and Australopithecus afarensis. A. ramidus, unlike modern hominins, has adaptations for both walking on two legs (bipedality) and life in the trees (arboreality).


Over time, hominins developed larger brains relative to body size, a process known as encephalization. This growth, especially in areas linked to problem-solving, planning, and language, marked a crucial transition towards more complex behaviours.

Teeth and Jaw

Evolving jaw morphology led to a reduction in prognathism (the forward jutting of the jaw), and the development of a more parabolic dental arcade, typical of modern humans.

The utilization of tools for processing food reduced the need for large, robust teeth and heavy jaws.

Homo sapiens, for instance, has much more delicate jaw, with smaller teeth reflecting a diverse diet, aided significantly by cooking techniques.

Culture and Stone Tools

The invention, use and development of stone tools ushered in the Stone Age, 3.3 million years ago.

These tools ranged from the simple Oldowan choppers to bifacial Acheulean handaxes, and Mousterian flake tools made from prepared cores, using Levallois-type flake removal technology, all the way down to the spear-throwers (atlatls), projectile points and micro-blades of the Upper Paleolithic.

These advancements, coupled with evidence of prehistoric art, ritual burials, and complex social structures, are key markers of cognitive progress and symbolic thinking.

Archaeology tells us that any art created prior to about 100,000 BC, was limited to body painting, face painting, ancient pottery, rudimentary abstract carvings, or cupules - the mysterious cup-shaped indentations on rock surfaces.

Rather surprisingly, Neanderthals created very little art during their 350,000 years on Earth. It wasn't until the emergence of modern H. sapiens that figurative cave painting appeared (43,500 BC in Indonesia) and prehistoric sculpture emerged (38,000 BC in Germany).

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Body Size of Hominins

Recent archaeogenetics research confirms that both early hominins and early humans tended to be small, compared to later species. It wan't until Homo erectus that humans began to develop a significantly larger average body size than earlier hominins.

In addition, a recent study has highlighted the variation in height within species.

Researchers studied four different groups of Homo erectus living around 1.8 million years ago, in different areas: namely, Olduvai Gorge, Tanzania; Koobi Fora, Kenya; Dmanisi, Georgia; and South Africa.

The average height and weight of these groups ranged from 166 cm (5 ft 5 in) and 71 kg (156 pounds) at Koobi Fora, to 166 cm (4 ft 8 in) and 50 kg (107 pounds) at Olduvai.

So tremendous variation in body size existed even within the same species.

Is Body Size Linked to Brain Size?

Answer: Yes. Body size is related to brain size. So as hominins became taller and heavier, their brain size increased as well.

Thus, while the smallest specimens of early Homo erectus had brain sizes only slightly larger than their australopithecine ancestors, large-bodied specimens, had a brain volume of more than 800 cubic centimetres, roughly 50 percent larger than australopiths (and about 60 percent of the typical brain size of a modern human).

In addition, as we mentioned, over time, hominins developed larger brains relative to body size, a process we call encephalization.

Which is why the cranial capacities of later H. erectus specimens are well in excess of 1000 cubic centimetres, (within the lower range of modern humans) without any increase in body size.

List of Known Hominin Species

The hominin family tree is diverse, with many branches and species. Some notable hominins include:

NEXT: Stone Age Culture: A-Z Fact sheet.


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