10.1: Early Hominins - Genus Homo

It is generally thought that by 2.5 mya, there was a species of Homo in East Africa, Homo habilis. The inclusion of those fossils in our genus is not accepted by all and is somewhat arbitrary. Some argue that H. habilis  does not differ enough from australopiths to warrant different genus designation. Its inclusion in Homo was prompted by the fact that they are thought to have made and used tools and thus to have been cognitively advanced. H. habilis  was more encephalized than the australopiths, and the skull vault is flexed as in Au. africanus, P. boisei, P. robustus, and later species of Homo.

Homo Habilis

The human genus, Homo, first appeared between 2.5 and 3 million years ago. Fossils of H. habilis  are the oldest examples in the genus Homo. Compared to A. africanus, H. habilis  had a number of features more similar to modern humans. H. habilis  had a jaw that was less prognathic than the australopiths and a larger brain, at 600–750 cubic centimeters. However, H. habilis  retained some features of older hominin species, such as long arms. The name H. habilis  means “handy man,” which is a reference to the stone tools that have been found with its remains.

Figure \(\PageIndex{1}\): KNM-ER 1813, Koobi Fora, Kenya. “Homo habilis-KNM ER 1813” by Locutus Borg is in the public domain.

Louis and Mary Leakey discovered the first fossil material in 1960 at their site in Olduvai Gorge, Tanzania. Louis had been recovering stone tools from the site for years, but the manufacturer of those tools had previously eluded him. He named the species Homo  habilis  or “handy-man.” Fossils attributed to H. habilis  have also been found at Hadar (and possibly Omo), Ethiopia; Koobi Fora, Kenya (see Figure); and the South African sites of Swartkrans and Sterkfontein.

H. habilis  exhibited a high degree of sexual dimorphism, with males and females weighing 114 and 70 lb and standing 5´2˝ and 4´1˝, respectively. Their skull, face, and dentition were more gracile than the australopiths. Their teeth and dental arcades were very human-like. The skull base was flexed, as seen in Au. africanus  and the more derived robust australopiths and, relative to past species, the skull was rounder and higher, reflecting architectural changes in the brain. Cranial capacity ranged from 500 to 800 cc with a mean of 631 cc. 

At this point in hominin evolutionary history, we see increased asymmetry in the two hemispheres of the brain, termed lateralization or left hemispheric dominance. The left side of our brain is involved with language and analytical processes. Like all Old World monkeys and apes, H. habilis  possessed Broca’s area, which is involved with language production. However, it was larger than in past hominin species, and they also possessed Wernicke’s area, which plays a role in language comprehension. They thus had the neural capacity for language. The left hemisphere is also related to right-handedness.

Like the majority of the australopiths, H. habilis  possessed elongated arms, possibly suggesting continued reliance on an arboreal environment. While the digits were still curved, they had increased gripping capabilities for tool manufacture and use, as evidenced by the pronounced attachment site for the flexor pollicis longus  muscle, which acts to flex the thumb.

Tool Use

Certainly one of the most interesting things about H. habilis the appearance of a much more extensive archaeological record. The cultural period at that time, and extending through  Homo erectus, is termed the Early Paleolithic, or the early portion of the Old Stone Age. While other species apparently preceded H. habilis  in the manufacture of tools, it was thought for many years that they were the first to do so.

The Oldowan  or Olduwan tradition (industry  and technology  are also used synonymously with “tradition”), named after Olduvai Gorge, consisted of simple core tools and flakes. The technique involved the selection of a cobble (a workable-sized rock), followed by the use of a hammerstone  to remove the outer rough surface (see Figure) or “cortex” and then to shape it into a core tool, by the removal of flakes. The flakes that are removed may be suitable for cutting and slicing. The process is called hard percussion, and the shaping is known as lithic reduction. “Lithic” refers to stone and is also used to denote a stone tool.

Stone resources for the manufacture of tools were chosen for their suitability and transported across the landscape. Of course, this indicates a level of cognitive complexity, but we must remember that chimps and orangutans choose sticks and grass of particular widths and strengths, trim them to the appropriate length, and transport them in their mouths to their site of intended use. Apes learn by trial and error, innovation and imitation, and cultural transmission, i.e., traits spread throughout a group by observation. Cultural transmission of innovations is even seen in monkeys, e.g. Japanese macaques washing sweet potatoes, skimming grain kernels floating on the surface to separate them from beach sand, and bathing in volcanic springs. 

The Oldowan tradition lasted from approximately 2.5 to 1.5 mya but survived in some areas until 600 kya. Tools consisted of crude choppers (see Figure \(\PageIndex{2}\)) and scrapers, as well as simple flake tools, some of which indicate that they were “retouched,” i.e., secondarily shaped and/or sharpened. In addition, there is evidence of possible wooden digging sticks or spears at the site of Koobi Fora, in the East Lake Turkana region of Kenya and possible bone tools at Olduvai Gorge.

Figure \(\PageIndex{2}\): Crude “chopping” tools

The Oldowan tradition lasted from approximately 2.5 to 1.5 mya but survived in some areas until 600 kya. Tools consisted of crude choppers and scrapers, as well as simple flake tools, some of which indicate that they were “retouched,” i.e. secondarily shaped and/or sharpened. In addition, there is evidence of possible wooden digging sticks or spears at the site of Koobi Fora, in the East Lake Turkana region of Kenya and possible bone tools at Olduvai Gorge.

Homo erectus

H. erectus appeared approximately 1.8 million years ago. It is believed to have originated in East Africa and was the first hominin species to migrate out of Africa. Fossils of H. erectus have been found in India, China, Java, and Europe, and were known in the past as “Java Man” or “Peking Man.” H.erectus had a number of features that were more similar to modern humans than those of H. habilis. H.erectus was larger in size than earlier hominins, reaching heights up to 1.85 meters and weighing up to 65 kilograms, which are sizes similar to those of modern humans. Its degree of sexual dimorphism was less than earlier species, with males being 20 to 30 percent larger than females, which is close to the size difference seen in our species.

H. erectus had a larger brain than earlier species at 775–1,100 cubic centimeters, which compares to the 1,130–1,260 cubic centimeters seen in modern human brains. H.erectus also had a nose with downward-facing nostrils similar to modern humans, rather than the forward facing nostrils found in other primates. Longer, downward-facing nostrils allow for the warming of cold air before it enters the lungs and may have been an adaptation to colder climates. Artifacts found with fossils of H. erectus suggest that it was the first hominin to use fire, hunt, and have a home base. H. erectus is generally thought to have lived until about 50,000 years ago.

H. ergaster	Hominins on the H. erectus lineage that are found in Africa
H. erectus	Hominins on the H. erectus lineage that left Africa and are found in Asia

Did H. habilis  give rise to Homo erectus/ ergaster (African form of the H. erectus)? Most likely not, since the species overlap in time and geographic space. While the size and architecture of the brain of H. habilis  make it a contender in the minds of some researchers, their limb proportions, i.e., retention of long arms and short legs, do not resemble H. erectus/ ergaster.

Homo ergaster

The earliest H. ergaster  material is from the East Lake Turkana site of Koobi Fora in Kenya. Richard Leakey is credited with this 1.8 mya discovery. Other sites outside of Africa are contemporary with African sites, e.g. the 1.8 mya Dmanisi site in the Republic of Georgia and the 1.8–1.6 mya site of Modjokerto in Java. (Note: There are problems with the Javanese dates because the fossil-containing layers are not conducive to more reliable dating methods.)

Figure \(\PageIndex{3}\): Reconstruction of Homo erectus. “Homo erectus new” by Lillyundfreya is licensed under CC BY-SA 3.0.

The almost complete Nariokotome or Turkana Boy (see Figure) from the West Lake Turkana region of Kenya was discovered in 1984 by Kamoya Kimeu and dated to 1.6 mya. The skeleton has been extremely important for reconstructing body morphology and limb proportions. The boy is thought to have been eight years old based upon tooth development patterns. He was formerly thought to be as old as 15, based on his height, stage of bone development, and hypothesized growth trajectories. However, dental calculations can accurately determine age due to the daily pattern of enamel deposition during tooth development.

Figure \(\PageIndex{4}\): “Turkana Boy” by Mike Peel is licensed under CC BY-SA 4.0.

Scientists can count the microscopic, bead-like deposits that are laid down daily during the course of a tooth’s development. Once it was determined that he was only eight years old yet 5´3˝ tall, it was apparent that H. ergaster  developed at a much faster rate, more like a chimp than a human. Had Turkana Boy lived to adulthood, he would have been over 6´ tall. His morphology was adapted to the hot, dry conditions in equatorial East Africa, i.e. tall and long-limbed, similar to modern peoples of the region.

Homo erectus

The most popularly held notion is that Homo erectus  is derived from H. ergaster or a pre-ergaster  form that “quickly” moved out of Africa into Eastern Europe and Southeast Asia. Eugène Dubois discovered the first H. erectus  material at the Trinil site on the Solo River in Java in 1891. While there are problems with the dates, the oldest material from the Javanese site of Modjokerto may be “contemporary” with African and Georgian material at 1.8 mya. Other famous Javanese sites are Sangiran, Ngandong, and Trinil. Java is part of the Sunda shelf, and when initially colonized by H. erectus, it was connected to mainland Asia

The first fossils were discovered at the now famous site of Zhoukoudian (formerly Choukoudian), near Beijing (formerly Peking and hence the term, “Peking Man”). The local people called them “dragon bones” and were using them for medicinal purposes. Material from Zhoukoudian spans a time period of over 200,000 years, from 460 to 230 kya, with three distinct cultural periods thought to be in evidence.

One of the great mysteries of paleoanthropology surrounds the Zhoukoudian material. Franz Weidenreich and his predecessors, Davidson Black and J. Gunnar Andersson, had amassed an unprecedented amount of fossil material from the site. Due to the imminent Japanese invasion, Weidenreich packed up the fossil material in 1941 with the intent of having it shipped to the United States. However, the material disappeared, and all that remains are Weidenreich’s notes, drawings, and some casts of the original fossils.

Homo erectus is characterized by a tall body and much larger brain than previous members of the genus. They exhibit a sagittal keel on the top of the skull due to thickening along the sagittal suture. The keel gives the skull a pentagonal shape.  

Culturally and technologically, Asian H. erectus  are thought to have been somewhat similar to African H. ergaster. The earliest inhabitants of Asia carried with them the Oldowan tool tradition. While nomadic, they are thought to have stayed in an area for at least short periods of time, relative to past species. Early H. ergaster  is associated with the Oldowan technology, and that is the technology that they took with them out of Africa. H. ergaster  subsequently invented a tool tradition, termed Acheulian, that first appears in the archaeological record at 1.4 mya (newer data suggests possibly as early as 1.7 mya) and lasted to as late as 115 kya in some areas.

Figure \(\PageIndex{5}\): Acheulian hand axe. “Bifaz en mano” by José-Manuel Benito Álvarez is licensed under CC BY-SA 2.5.

The latter industry spread throughout Africa and as far-east as the Indian subcontinent and west to Western Europe. It involved the use of better stone resources and tools that were more refined and standardized than in the Oldowan tradition. The most representative tool was a bifacially worked (shaped on both sides) hand axe in the shape of a teardrop (see Figure). Populations of H. erectus  survived in Asia for much of the Pleistocene Epoch. Recent redating of the Javanese site of Ngandong has yielded dates as recent as 53–27 kya.

Homo floresiensis

The material assigned to the species Homo floresiensis  comes only from the cave site of Liang Bua on the island of Flores in Indonesia. Because of its diminutive size, the new species took the world by storm when it was discovered in 2003 by Mike Morwood and his team. While tools attributed to the species have been dated to almost 100 kya, skeletal remains are dated to as young as 18 kya and as old as 95–74 kya (Brown et al. 2004).

The recent discovery of dwarfed hominins on the island of Flores, termed H. floresiensis, that have been dated to 18 kya. H. floresiensis  is thought to be descended from a population of H. erectus  that adapted to limited island resources by becoming dwarfed in size.

Figure \(\PageIndex{6}\): Homo floresiensis. “Homo floresiensis” by Ryan Somma is licensed

While there is controversy surrounding this strange species, H. floresiensis  is thought to have descended from a group of H. erectus  that traveled across the sea from mainland Asia. Once there, they adapted to the island via a process known as insular  or island dwarfism. Large mammalian species that become isolated on islands tend to decrease in size over time (as opposed to reptiles and small mammals that may increase in size), as smaller individuals require less food and thus have a better chance of survival and reproduction, when faced with limited space and resources and low risk of predation.

At only ~3.5′ (1.06 m) tall and 35–79 lb (16–36 kg), LB1 is very small relative to H. erectus, falling at the low end of H. habilis. Even more incredible is her brain size of 380 cc. Yet her encephalization quotient is estimated at 2.5–4.6. When compared with the brains of H. erectus  and H. ergaster  at 3.6–4.3 and H. habilis  at 3.6–4.3, her brain is not as small as it first appears. However primitive her skeletal characteristics, the complexity of the cultural remains, and the size of an important association area of the prefrontal cortex do not support the microcephaly argument.

They made and used tools, as evidenced by the presence of sharpened tools, prepared cores for the production of tools, debitage from their manufacture, anvils, etc., along with faunal remains from a variety of species, such as stegodon, komodo dragons, rats, and bats. Their tools were small, compatible with their small body size. Burnt bones, fire-cracked rock, and a possible hearth consisting of a circle of fired rocks show that they made use of fire.

The hominins may have survived until 12 kya when a volcanic eruption may have caused their extinction, as well as that of the dwarf stegodon. Since Flores was not inhabited when discovered by Portuguese traders in the 15th century, they may never have coexisted with modern humans

Contributors and Attributions

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