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Prehistoric World

Hominid Chronology

by Peter Kessler, 26 July 2005. Updated 26 April 2017

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A SEVEN PART FEATURE:
Part 1: 20 million years
Part 2: 3.9 million years
Part 3: 2.3 million years
Part 4: 1.9 million years
Part 5: 600,000 years
Part 6: 350,000 years
Part 7: 200,000 years

 

Almost human
 

1.9 million

Homo ergaster
Part 1 of 3 Skip forwards

The first truly human-like hominid species was Homo ergaster ('workman'). This species evolved either from Homo rudolfensis or Homo habilis during an accelerated period of global cooling and drying which cleared more and more tropical rainforest from Africa and regularly created a desert in the northern half of the continent.

Until recently, the general consensus was that habilis was the more likely ancestor, but finds from Kenya in 2007 revealed an overlap of about 500,000 years during which habilis and ergaster must have co-existed in the Turkana basin area, the region of East Africa in which the fossils were unearthed. Their co-existence seems to make it less likely that ergaster evolved from habilis.

If ergaster had evolved from [a group of] habilis and remained within the same location as other habilis groups then both must have been in direct competition for the same resources. Eventually, one would have out-competed the other. However, the fact that they stayed separate as individual species for a long time suggests that they had their own distinct ecological niches, therefore avoiding direct competition.

As if the choice were not already uncertain enough, an alternative theory formed in 2011 suggests that both rudolfensis and habilis are instead cousins and ergaster actually descends directly from Australopithecus sediba.

Homo ergaster typically possessed a thick, bony brow ridge across the eyes, large teeth sticking out from a vaguely apelike projecting mouth below a long, wide nose, and long limbs. Individuals seem to have grown to a height of around 185cm (six feet one inch) with a body shape that was perfectly adapted to an active life in the sun (just as with modern human populations living on equatorial grasslands today, such as the Masai in Kenya). This body shape creates a large surface area over which the body can cool itself more easily, preventing Homo ergaster from overheating under the blazing sun.

This hominid was probably the first to regulate its temperature through sweating. For creatures which must remain active at midday in a sunny, dry habitat, sweating is the most effective mechanism for maintaining safe body and brain temperatures. Homo ergaster's body was probably smooth and largely hairless, since heat loss through sweating occurs most efficiently through naked skin. Its skin was almost certainly dark, to protect it from the sun's harmful rays.

Homo ergaster travelled long distances on foot, as it worked hard to scavenge enough meat to feed its growing body and brain. In order to increase the energy efficiency of muscles involved in upright walking, ergaster developed a narrower pelvis. But its snake hips came at a price.

Firstly, the narrowing of the pelvis caused the lower part of the ribcage to narrow. In order to prevent constriction of the lungs, the upper part of ergaster's rib cage expanded, giving its chest a human barrel shape. Secondly, and more importantly, the narrowing of the pelvis constricted the female birth canal. This single anatomical change seems to have had profound consequences for human relationships.

Homo ergaster, Turkhana Boy
In general, the use of Homo ergaster describes a species of hominid in Africa, but when examples of the same species leave Africa they are generally referred to as Homo erectus, although this is not a hard or fast rule - this example belongs to Turkana Boy, otherwise known as Nariokotome Boy, the most complete skeleton found to date and a perfect example of Homo ergaster of about 1.5 million years ago


A tight pelvis could have caused problems during birth. As brains increased in size, mothers had to push increasingly big-brained infants through an already tight pelvis. The solution was a trade-off. While chimpanzees are born with their brains almost fully mature, humans are born with a comparatively immature brain. This makes human babies helpless and vulnerable during their first year of life as their brains make vital neural connections.

As a result, human mothers need to be well nourished to keep up with the demands of their babies, making them increasingly reliant on the support of their male partner and other members of their social group. Many experts regard this shift as the beginning of the nuclear family.

Climate variations in East Africa may also have influenced hominid development. Scientists have identified lake systems which formed and disappeared in East Africa between one and three million years ago, providing possible evidence that global climate changes were occurring.

There were three distinct periods during which extensive lakes covered the region and grew to depths of hundreds of metres. The growth of these lakes probably resulted from a moist local climate. The regional wet periods, which may have persisted for up to 100,000 years, occurred as much of Africa became increasingly dry.

The periods of wet weather in East Africa may reflect fluctuations of the Earth's climate as a whole. At the time at which the lakes grew - and this period was one of them - glaciers and the atmosphere were also going through major transformations.

This provides strong support for theories in which early human species evolved and spread out in response to a rapidly changing environment.

 

1.9 million

Paranthropus robustus

At the same time as Homo ergaster was emerging in Africa, Paranthropus boisei's southern African relative, Paranthropus robustus ('robust') also appeared.

P robustus was initially thought to have survived until 1.4 million years ago, a span of 500,000 years. This figure has since been revised down to 1.2 million years. It is uncertain if it evolved from the same ancestor as boisei or if, as is argued by some researchers, robustus is a case of parallel evolution in that it may have descended directly from Australopithecus africanus.

Evidence of what robustus was eating is less clear than for its northern 'relative'. They seem to have been consuming grass-eating insects, including termites. Archaeological finds show that robustus dug termites out of their mounds using sharpened animal bones. It could also have been eating the roots of plants such as papyrus.

The species name was chosen to describe the skull, jaw, and teeth, which were much more dense and thicker than what had been seen in previous species. There were also many more ridges and crests located on the skull. The front teeth of robustus were smaller, but the molars in the back were larger than with previous species. These dental characteristics support theories about the species' diet.

An advancement which appeared both with robustus and boisei was the presence of a sagittal crest, a ridge which ran from front to back on top of the skull in which muscles were attached. These muscles aided in moving the jaw so that chewing was possible. As more muscle was formed more powerful chewing was possible.

Most researchers agree that boisei and robustus are separate species rather than a widely-spread single, but variable, species. A small minority insist on refusing to accept the Paranthropus classification for them, referring to them instead as Australopithecus robustus.

 

Homo erectus

Out of Africa I
 

1.8 million

Homo erectus
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Shortly after Homo ergaster appeared, humans began to leave Africa for what was long thought to be the first time and migrate to other continents. This has since been disproved with the discovery of Homo georgicus at Dmanisi in Georgia.

Homo ergaster migrants were forced to hunt for new foodstocks by progressively cooler global temperatures at the start of the Pleistocene era. After groups of ergaster left Africa they are referred to as Homo erectus ('upright man') - an older term which formerly included a large range of specimen types. H erectus survived mainly in South Asia, while H ergaster remained in Africa as a direct ancestor of modern man. [1]

Homo erectus' migration took place during a rather brief period called the Olduvai subchron (1.98 to 1.79 million years ago). The East African Rift and extreme South East Asia were endpoints on a grand east-west geotectonic pathway called the Tethys corridor, a feature which was extremely unstable. Homo erectus and companion mammals took advantage of open linear landscapes to migrate north from the Rift to the Caucasus, and then both ways across the Tethys corridor - west towards Gibraltar and east to the Himalayan foreslope.

Homo erectus reached Dmanisi, which is eighty kilometres (fifty miles) south-west of the Georgian capital, Tbilisi, at around 1.8 million years ago. Here they encountered cool, seasonal grasslands where African animals such as ostriches, rhinoceros and giraffes mingled with Eurasian species such as wolves and the sabre-toothed cat megantereon. This is where they also encountered the diminutive Homo georgicus.

[1] There is, typically, some debate about the validity of Homo ergaster as a separate sub-species, with many seeing it as no different to an African-bound Homo erectus, a generalised classification inherited from the days before more than two Homo species were known. For the purpose of clarity, ergaster is used to refer to the African type while erectus is used for populations outside Africa - this being the most widely-used method of labelling them.

Homo erectus quickly spread further east to the emergent Sunda continental shelf off East Asia's present south coast, before rising sea levels cut the shelf into a series of islands of which the modern Indonesian island of Java is the southernmost.

Populations existed throughout subtropical Asia, but extended no further north than the Himalayas or southern China. Instead, erectus learned to survive in the bamboo forests that covered this region of Asia. The paucity of stone tools from South East Asian hominid sites suggests that erectus may have created a technology based on bamboo, a strong and versatile material.

'They may have used bamboo to make spears for hunting and poles to knock animals down from the tall trees,' saids Professor Russell Ciochon of the University of Iowa. Homo erectus shared these bamboo forests with pigs, a type of elephant called Stegodon and the biggest primate that has ever lived: the giant vegetarian ape Gigantopithecus - a descendant of the earlier Ramapithecus or Sivapithecus. It is possible that Gigantopithecus may even have been hunted by early humans in Asia. 'They probably wouldn't have taken on the big adults, but they may have targeted juveniles. If we look at people who live in forests today, they also eat apes,' said Ciochon.

Dates for the arrival of Homo erectus in subtropical Asia are controversial. While erectus was clearly established throughout the region by 1.8 million years ago, some sites suggest an even earlier date for its arrival. A hominid jaw and stone tools unearthed at Longuppo Cave in China may date to as early as 1.9 million years ago - 100,000 years earlier than expected.

Similar dates have been established for hominid sites at Mojokerto and Sangiran in Java. This newfound wanderlust may have been dictated by an increasing reliance on meat for food. Carnivores generally need much larger home ranges than similar-sized herbivores because carnivores have fewer total calories available to them per unit area of their territory.

Gigantopithecus

Find out more about primitive hominoids (click on image to read more on a separate page)

Shortly after settling in its new Asian homelands, from about 1.6 million years ago Homo erectus began to diverge from Homo ergaster populations. This divergence may be related to the first full scale Ice Age, which occurred around 1.5 million years ago, following half a million years of continued cooling of the world climate.

 

1.8 million?

Homo naledi

Homo naledi made worldwide headlines in 2015 when researchers announced the discovery of an unusually large collection of odd-looking Homo fossils in the bowels of South Africa's Rising Star cave system.

The cave - the Dinaledi Chamber - was extremely hard to reach, being accessed via narrow passageways and down a vertical chute which only the more slender experts could manage. The level of difficulty in reaching the site left archaeologists puzzling over how the bones got there in the first place. They recovered 1,550 fossils from a minimum of fifteen individuals of all age groups. Some experts have asserted that naledi intentionally dropped dead comrades into the underground chamber, but that's far from proven yet.

One of the biggest mysteries surrounding naledi has been its age. A solid date for the fossils is essential for deciphering their place in Homo evolution.

The archaeological team assigned the bones to H naledi based on an unexpected mix of humanlike features and traits which are typical of Australopithecus species from more than three million years ago. Fossil analyses have challenged the speculative claim that naledi actually represents a variant of Homo erectus, a species known to have existed by 1.8 million years ago.

In fact, naledi possessed a shoulder unlike those of other Homo species. Its collarbone and upper arm bone resemble corresponding Australopithecus bones. The shoulder blades must have been positioned low and behind the chest, an arrangement more conducive to climbing trees than running long distances. H naledi's hand was built both for climbing and gripping stone implements. It had a human-like wrist and thumb which were combined with Australopithecus-like curved fingers.

Homo naledi
The lower jaw of Homo naledi (on the left) is not as strongly built as those of many hominins, while the hand (right) has a very human shape but the curved finger bones and strong thumb are archaic features (text partially from the Natural History Museum, London)


Its curved toes and flaring pelvis also recall Australopithecus. Still, a preliminary lower-body reconstruction - incorporating fossil evidence of humanlike legs, knees, and feet - suggests that naledi walked almost as well as modern humans.

Dating remained unconfirmed at the start of 2017, but a window between 2 million years and 1.5 million years seemed most likely based on similarities in the skull and other body parts to other species in this timescale.

One late-2016 estimate which has been claimed as reasonably reliable (although possibly using a flawed process of analysis) suggests a date as recent at 912,000 years, which would place it in Africa at the same time as Homo ergaster. A young date for naledi perhaps should not be unexpected. At least some naledi bones appear not to have fossilised, which would be consistent with a more recent age.

A study released in April 2017 suggested a date for the remains of 300,000-200,000 years ago, making naledi contemporary with Neanderthals.

 

1.77 million

Homo georgicus / Dmanisi Man

Once in the Caucasus, Homo erectus may have discovered that it was not the only hominid living in the region. There is also evidence to suggest that a group of hominids of a much smaller stature were established there.

A collection of 1991 finds from Dmanisi (sometimes shown as Dimanisi) in Georgia in the same layer of sediment as Homo erectus finds has brought to light these little 'people' - who stood at around four feet tall - but this has caused a lively debate amongst palaeoanthropologists.

So far it has been tricky to work out exactly what species they are. Common thought is that Homo erectus was the first to venture out of Africa and spread around Asia. But the Dmanisi hominids were not typical of the tall-standing, big brained erectus - instead they were short, long-armed, small-brained, and thin browed, with a far smaller brain cavity - half the size of a modern human - and the huge canine teeth and thin brow of an ape.

However, the tools found alongside fossils were basic choppers and cutters, just like those found at the sites of early, primitive humans in Africa. There were no signs at the archaeological sites of fire having been used (not unusual though, as fire seems first to have been 'tamed' by H ergaster around 1.0 million years ago.

This has led some to believe they may have been Homo habilis. But the relatively ape-like habilis was not thought to have lived outside Africa. Other researchers have coined the term Homo georgicus to describe the finds, and this seems to be sticking, for now.

 

1.76 million

Homo ergaster
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In 2011, the world's earliest sophisticated stone tools were found near Lake Turkana in north-west Kenya.

The teardrop-shaped hand-axes date to about 1.76 million years ago, and would have been used for a range of tasks from chopping wood to cutting up meat. They would have been so useful that scientists describe them as the 'Swiss army knife' of the Stone Age. The tools were probably made by Homo ergaster.

The type of tools unearthed at the Kokiselei archaeological site are referred to by anthropologists as Acheulian technology. They are larger and heavier than the pebble-choppers (Oldowan technology) which were used by ergaster's predecessor, Homo habilis. The Acheulian hand-axes, known as 'bifaces', also have distinctive chiselled edges. Manufacturing them would have required forethought in design and the careful selection of particular types of starting rocks from which to fashion the final product.

The study shows that the tools were in use some 350,000 years earlier than all previous Acheulian finds. This dating places them closer to the origins of Homo ergaster, and suggests the Acheulian was the proprietary technology of this specific human species. This invention by ergaster would seem to have happened shortly after the migration of Homo erectus into Asia, which is backed up by the fact that it took hundreds of thousands of years for the technology to become widespread elsewhere in the world.

 

1.6 million

Less differences between the sexes in Homo ergaster than in previous hominids may reflect a distinctively human pattern of sharing and cooperation between males and females. Homo ergaster probably communicated using gestures combined with a limited range of sounds. Their vertebral canals do not seem to have been developed enough to have given them the control over the breathing needed for complex speech.

H ergaster also seems to have relied more than previous hominids on stone tools for processing food. Although to begin with, ergaster used the aforementioned primitive Oldowan tools, its symmetrical, heart-shaped Acheulian hand axes gave the hominid greater control over the butchering of meat for food.

Again, this seems to be related to changing conditions caused by the occurrence of the first Ice Age. Hereafter, Ice Ages occurred at fairly regular intervals of 80,000 to 100,000 years: dramatic falls in temperature and the formation of extensive ice sheets, especially in the northern hemisphere, alternated with warmer periods when temperatures were similar to those of the present day.

One of the best sources of information about Homo ergaster is a skeleton discovered in 1984 by Alan Walker and Kamoya Kimeu at Nariokotome in West Turkana, Kenya. The remains were found to be those of a teenage boy between the ages of eleven and thirteen when he died. Around 1.5 million years ago, the boy's body sank into the marsh where he died and became fossilised.

His teeth show signs of an abscess where his milk teeth fell out, indicating that he may have died from septicaemia (blood poisoning). Nariokotome Boy, as he has been dubbed, was already developing a thick, bony brow ridge above his eyes. A pair of buck teeth stuck out from a large, projecting mouth below a long, wide nose. He was about 160 centimetres (five feet three inches) tall and would have stood at 185 centimetres (six feet one inch) had he reached adulthood. This was clearly a strapping lad, with a body shape that was perfectly adapted to an active life in the sun.

Human populations living on equatorial grasslands today, such as the Masai in Kenya, have the same tall, linear physique. This body shape creates a large surface area over which the body can cool itself more easily, preventing Nariokotome Boy from overheating under the blazing sun.

 

1.2 million

Paranthropus boisei
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Paranthropus boisei eventually paid the price for being a specialist in a changing world. The onset of successive ice ages spelt the end.

The largest boisei skull specimen found is dated to 1.4 million years old, discovered at Konso in Ethiopia. Some individuals have been found in stratigraphic layers with tools, and also with Homo specimens who often made tools, so there's no clear answer to the question of whether boisei itself used stone tools.

Despite its successful way of exploiting the savannah - from its taste for termites to the wide range of vegetation it had specialised in eating - boisei became a footnote in human prehistory. The species was driven to extinction, probably by an intense period of cooling and drying caused by an ice age.

P boisei was unable to adapt to this new, rapidly changing environment. When Earth's climate became intensely irregular, with fluctuating hot and cold spells, there may have been changes in the proportions of food resources available to boisei. Certain plants could have dwindled or died out. A species' ability to adapt to changing resources, like food, is critical to their survival. Was the highly specialised boisei unable to adapt if some of their favoured plant foods disappeared due to climatic changes? This is the most likely hypothesis at present.

Paranthropus boisei
Like other members of the Paranthropus genus, boisei is characterised by a specialised skull with adaptations for heavy chewing - the strong sagittal crest on the midline of the top of the skull anchored the temporalis muscles (large chewing muscles)

 

1.0 million

Homo erectus
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Homo erectus was still dominant in South Asia, living in small, semi-isolated groups. One such erectus group (according to available but still-controversial evidence) seems to have managed to make its way by sea - despite sea travel previously being thought beyond erectus' capabilities - to the island of Flores in Indonesia (one of a chain of islands stretching east from Java), where by 800,000 years ago it was making stone tools. The limited resources on the island seem to have forced this group to evolve into Homo floresiensis.

H erectus was already known to have made its way to Java, perhaps as early as 1.5 million years ago. This is where the earliest-known erectus fossils were discovered in the early 1890s (and were initially called Java Man).

Flores was never connected by land bridges either to Asia or Australia. Even at times of low sea level, island-hopping to Flores from mainland Asia involved sea crossings of up to twenty-four kilometres (fifteen miles). The only land mammals here were stegodonts (extinct elephant ancestors) and rodents, the former by swimming and the latter by hitching a ride on flotsam. Since erectus is unlikely to have had the brainpower to fashion a boat, the most likely answer is that it saw something else swimming towards the island and copied it, but possibly with the help of floating debris.

Other erectus groups were beginning to move into Europe, although their presence there would never be very great.

 

1.0 million

Homo ergaster
Skip backwards Part 3 of 3

Fossil finds in Kenya dated to 930,000 years ago suggest that Homo ergaster was still dominant in Africa. It seems to have become the first hominid to use fire, which enabled it to eat food more easily and also allowed the size of its jaws and teeth to reduce. This resulted in some variation in skull sizes occurring, marking out demonstrable differences at this time between ergaster and Homo erectus.

Fire may have been used as long as 1.5 million years ago for cooking and warmth but whether this was a controlled use of fire is not certain. Charcoal, burnt earth, and charred bones found associated with ergaster fossils may have resulted from naturally occurring fires rather than from intentionally lit and controlled fires.

Recent reports (Current Anthropology Vol 52, 4 August 2011) of discoveries in Wonderwerk Cave, South Africa, suggest controlled use of fire may have been occurring by 1.7 million years ago. Stratified deposits contain burnt stones, charred-calcined bones and traces of ash which indicate repeated burning events. The discoverers concluded that the fire-makers, most likely ergaster, regularly gathered around the fire to prepare and cook food and also for social reasons.

It is possible that the changes in ergaster were partly the result of the new Ice Age, which was already bringing climate changes with it. Whatever the cause, the appearance of Homo heidelbergensis was imminent.

 

 

 

Main Sources

Australian Museum

BBC series - Walking with Cavemen, first screened from 1 April 2003

Becoming Human

Bradshaw Foundation - Exploring the Fossil Record: Homo erectus georgicus

Bradshaw Foundation - Exploring the Fossil Record: Paranthropus boisei

Encyclopaedia Britannica

National Geographic

Science News - Magazine of the Society for Science and the Public

Smithsonian National Museum of Natural History

 

 

 

     
Images copyright BBC or affiliates unless otherwise stated. No breach of copyright is intended or inferred. Text copyright P L Kessler, adapted from numerous sources and notes. An original feature for the History Files.