10.2: Homo Habilis

THE EARLIEST MEMBERS OF OUR GENUS

Homo habilis has traditionally been considered the earliest species placed in the genus Homo. However, as we will see, there is substantial disagreement among paleoanthropologists about the fossils classified as Homo habilis, including whether they come from a single or multiple species, or even whether they should be part of the genus Homo at all.

Compared to the australopithecines in the previous chapter, Homo habilis has a somewhat larger brain size–an average of 650 cubic centimeters (cc) compared to less than 500 cc for Australopithecus. Additionally, the skull is more rounded and the face less prognathic. However, the postcranial remains show a body size and proportions similar to Australopithecus.

Known dates for fossils identified as Homo habilis range from about 2.5 million years ago to 1.7 million years ago. Recently, a partial lower jaw dated to 2.8 million years from the site of Ledi-Gararu in Ethiopia has been tentatively identified as belonging to the genus Homo (Villmoare et al. 2015). If this classification holds up, it would push the origins of our genus back even further.

Figure \(\PageIndex{1}\): Map showing major sites where Homo habilis fossils have been found.

Discovery and Naming

The first fossils to be named Homo habilis were discovered at the site of Olduvai Gorge in Tanzania, East Africa, by members of a team led by Louis and Mary Leakey (Figure \(\PageIndex{1}\)). The Leakey family had been conducting fieldwork in the area since the 1930s and had discovered other hominin fossils at the site, such as the robust Australopithecus boisei. The key specimen, a juvenile individual, was actually found by their 20-year-old son Jonathan Leakey. Louis Leakey invited South African paleoanthropologist Philip Tobias and British anatomist John Napier to reconstruct and analyze the remains. The fossil of the juvenile shown in Figure \(\PageIndex{2}\) (now known as OH-7) consisted of a lower jaw, parts of the parietal bones of the skull, and some hand and finger bones. Potassium-argon dating of the rock layers showed that the fossil dated to about 1.75 million years. In 1964, the team published their findings in the scientific journal Nature (Leakey et al. 1964). As described in the publication, the new fossils had smaller molar teeth that were less “bulgy” than australopithecine teeth. Although the primary specimen was not yet fully grown, an estimate of its anticipated adult brain size would make it somewhat larger-brained than australopithecines such as A. africanus. The hand bones were similar to humans’ in that they were capable of a precision grip. This increased the likelihood that stone tools found earlier at Olduvai Gorge were made by this group of hominins. Based on these findings, the authors inferred that it was a new species that should be classified in the genus Homo. They gave it the name Homo habilis, meaning “handy” or “skilled.”

Figure \(\PageIndex{2}\): Homo habilis fossil specimens. From left to right they are: OH-24 (found at Olduvai Gorge), KNM-ER-1813 (from Koobi Fora, Kenya), and the jaw of OH-7, which was the type specimen found in 1960 at Olduvai Gorge, Tanzania.

Controversies over Classification of Homo habilis

 

Table \(\PageIndex{1}\): Key Homo habilis fossil locations and the corresponding fossils and dates.

Location of Fossils	Dates	Description
Ledi-Gararu, Ethiopia	2.8 mya	Partial lower jaw with evidence of both Australopithecus and Homo traits; tentatively considered oldest Early Homo fossil evidence.
Olduvai Gorge, Tanzania	1.7 mya to 1.8 mya	Several different specimens classified as Homo habilis, including the type specimen found by Leakey, a relatively complete foot, and a skull with a cranial capacity of about 600 cc.
Koobi Fora, Lake Turkana Basin, Kenya	1.9 mya	Several fossils from the Lake Turkana basin show considerable size differences, leading some anthropologists to classify the larger specimen (KNM-ER-1470) as a separate species, Homo rudolfensis.
Sterkfontein and other possible South African cave sites	about 1.7 mya	South African caves have yielded fragmentary remains identified as Homo habilis, but secure dates and specifics about the fossils are lacking.

How Many Species of Homo habilis?

Since this initial discovery, more fossils classified as Homo habilis were discovered in sites in East and South Africa in the 1970s and 1980s (Table \(\PageIndex{1}\)). As more fossils joined the ranks of Homo habilis, several trends became apparent. First, the fossils were quite variable. While some resembled the fossil specimen first published by Leakey and colleagues, others had larger cranial capacity and tooth size. A well-preserved fossil skull from East Lake Turkana labeled KNM-ER-1470 displayed a larger cranial size along with a strikingly wide face reminiscent of a robust australopithecine. The diversity of the Homo habilis fossils prompted some scientists to question whether they displayed too much variation to all remain as part of the same species. They proposed splitting the fossils into at least two groups. The first group resembling the original small-brained specimen would retain the species name Homo habilis; the second group consisting of the larger-brained fossils such as KNM-ER-1470 would be assigned the new name of Homo rudolfensis (see Figure \(\PageIndex{3}\)). Researchers who favored keeping all fossils in Homo habilis argued that sexual dimorphism, adaptation to local environments, or developmental plasticity could be the cause of the differences. For example, modern human body size and body proportions are influenced by variations in climates and nutritional circumstances.

Definition: developmental plasticity

 The capability of an organism to modify its phenotype during development in response to environmental cues.

Given the incomplete and fragmentary fossil record from this time period, it is not surprising that classification has proved contentious. As a scholarly consensus has not yet emerged on the classification status of early Homo, this text will make use of the single (inclusive) Homo habilis species designation.

Homo habilis: Homo or Australopithecus?

There is also disagreement on whether Homo habilis legitimately belongs in the genus Homo. Most of the fossils first classified as Homo habilis consisted mainly of skulls and teeth. When arm, leg, and foot bones were later found, making it possible to estimate body size, they turned out to be quite small in stature with long arms and short legs. Analysis of the relative strength of limb bones suggested that the species, though bipedal, was much more adapted to arboreal climbing than Homo erectus and Homo sapiens (Ruff 2009). This has prompted some scientists to question whether Homo habilis behaved more like an australopithecine—with a shorter gait and the ability to move around in the trees (Wood and Collard 1999). They also questioned whether the brain size of Homo habilis was really that much larger than that of Australopithecus. They have proposed reclassifying some or all of the Homo habilis fossils into the genus Australopithecus, or even placing them into a newly created genus (Wood 2014).

Figure \(\PageIndex{3}\): Cast of the Homo habilis cranium KNM-ER-1470. This cranium has a wide, flat face, larger brain size, and larger teeth than other Homo habilis fossils, leading some scientists to give it a separate species name, Homo rudolfensis.

Other scholars have interpreted the fossil evidence differently. A recent reanalysis of Homo habilis/rudolfensis fossils concluded that they sort into the genus Homo rather than Australopithecus (Table \(\PageIndex{2}\)). In particular, statistical analysis performed indicates that the Homo habilis fossils differ significantly in average cranial capacity from the australopithecines. They also note that some australopithecine species such as the recently discovered Australopithecus sediba have relatively long legs, so body size may not have been as significant as brain- and tooth-size differences (Anton et al. 2014).

Table \(\PageIndex{2}\): Summary features of Homo habilis.

Hominin	Homo habilis
Dates	2.5 million years ago to 1.7 million years ago
Region(s)	East and South Africa
Famous Discoveries	Olduvai Gorge, Tanzania; Koobi Fora, Kenya; Sterkfontein, South Africa
Brain Size	650 cc average (range from 510 cc to 775 cc)
Dentition	Smaller teeth with thinner enamel compared to Australopithecus; parabolic dental arcade shape
Cranial Features	Rounder cranium and less facial prognathism than Australopithecus
Postcranial Features	Small stature; similar body plan to Australopithecus
Culture	Oldowan tools

HOMO HABILIS CULTURE AND LIFEWAYS

Early Stone Tools

The larger brains and smaller teeth of early Homo are linked to a different adaptive strategy than that of earlier hominins—one dependent on modifying rocks to make stone tools and exploit new food sources. Based on what we know from nonhuman-primate tool use, it is assumed that all hominins used tools of some sort. For example, australopithecines could have used digging sticks to extract the roots and tubers that were part of some species’ diets (though tools made from perishable material would leave no trace). As discussed in the previous chapter, stone tools almost certainly predated Homo habilis (possibly by Australopithecus garhi or the species responsible for the tools from Kenya dating to 3.7 million years ago). However, stone tools become more frequent at sites dating to about 2 million years ago, the time of Homo habilis (Roche, Blumenschine, and Shea 2009). This suggests that these hominins were increasingly reliant on stone tools to make a living.

Stone tools are assigned a good deal of importance in the study of human origins. Studying the form of the tools, the raw materials selected, and how they were made and used can provide insight into the thought processes of early humans and how they modified their environment in order to survive. Paleoanthropologists have traditionally classified collections of stone tools into industries, based on their form and mode of manufacture. There is not an exact correspondence between a tool industry and a hominin species; however, some general associations can be made between tool industries and particular hominins, locations, and time periods. The names for the four primary tool industries in human evolution (from oldest to most recent) are the Oldowan, Acheulean, Mousterian, and Upper Paleolithic.

The oldest stone tool industry is the Oldowan, named after the site of Olduvai Gorge where the tools were first discovered. The time period of the Oldowan is generally considered to last from about 2.5 mya to 1.6 mya. The tools of this industry are described as “flake and chopper” tools—the choppers consisting of stone cobbles with a few flakes struck off them (Figure \(\PageIndex{4}\)). To a casual observer, these tools might not look much different from randomly broken rocks. However, they are harder to make than their crude appearance suggests. The rock selected as the core must be struck by the rock serving as a hammerstone at just the right angle so that one or more flat flakes are removed. This requires selecting rocks that will fracture predictably instead of chunking, as well as the ability to plan ahead and envision the steps needed to create the finished product. The process leaves both the core and the flakes with sharp cutting edges that can be used for a variety of purposes.

Figure \(\PageIndex{4}\): Drawing of an Oldowan-style tool. This drawing shows a chopper; the flakes removed from the cores functioned as cutting tools.

Stone Tool Use and the Diet of Early Homo

What were the hominins doing with the tools? One key activity seems to have been butchering animals. Animal bones with cutmarks start appearing at sites with Oldowan tools. Studies of animal bones at the site show leg bones are often cracked open, suggesting that they were extracting the marrow from the bone cavities. It is interesting to consider whether the hominins hunted these animals or acquired them through other means. The butchered bones come from a variety of African mammals, ranging from small antelope to animals as big as wildebeest and elephants! It is difficult to envision slow, small-bodied Homo habilis with their Oldowan tools bringing down such large animals. One possibility is that the hominins were scavenging carcasses from lions and other large cats. Paleoanthropologist Robert Blumenschine has evaluated the scavenging hypothesis by directly observing the behavior of present-day animal carnivores and scavengers on the African savanna. From this, he inferred that there were scavenging opportunities for Plio-pleistocene hominins. When lions abandon a kill after eating their fill, scavenging animals arrive almost immediately to pick apart the carcass. By the time the slow-footed hominins arrived on the scene, the carcass would be mostly stripped of meat. However, if hominins could use stone tools to break into the leg bone cavities, they could get to the marrow, a fatty, calorie-dense source of protein (Blumenschine et al 1987).

Reconstructing activities that happened millions of years ago is obviously a difficult undertaking, and there is an active debate among anthropologists about whether scavenging or hunting was more commonly practiced during this time. Regardless of how they were acquiring the meat, all these activities suggest an important dietary shift from the way that the australopithecines were eating. The Oldowan toolmakers were exploiting a new ecological niche that provided them with more protein and calories. And it was not just limited to meat-eating—stone tool use could have made available numerous other subsistence opportunities. A study of microscopic wear patterns on a sample of Oldowan tools indicates that they were used for processing plant materials such as wood, roots or tubers, and grass seeds and stems (Lemorini et al. 2014). In fact, it has been pointed out that the Oldowan toolmakers’ cutting ability (whether for the purposes of consuming meat and plants or for making tools, shelters or clothing) represents a new and unique innovation, never seen before in the natural world! (Roche, Blumenschine, and Shea 2009).

Overall, increasing use of stone tools allowed hominins to expand their ecological niche and exert more control over their environment. As we’ll see shortly, this pattern continued and became more pronounced with Homo erectus.

REFERENCES

Anton, Susan C., Richard Potts, and Leslie C. Aiello. 2014. “Evolution of Early Homo: An Integrated Biological Perspective.” Science 345 (6192) doi: 10.1126/science.1236828.

Blumenschine, Robert, Henry T. Bunn, Valerius Geist, Fumiko Ikawa-Smith, Curtis W. Marean, Anthony G. Payne, John Tooby, J. Nikolaas, and Van Der Merwe. 1987. “Characteristics of an Early Hominid Scavenging Niche [and Comments and Reply].” Current Anthropology 28 (4): 383–407.

Leakey, Louis S. B., Phillip V. Tobias, and John R. Napier. 1964. “A New Species of Genus Homo from Olduvai Gorge.” Nature 202: 308–312.

Lemorini, Cristina, Thomas W. Plummer, David R. Braun, Alyssa N. Crittenden, Peter W. Ditchfield, Laura C. Bishop, Fritz Hertel, James S. Oliver, Frank W. Marlowe, Margaret J. Schoeninger, and Richard Potts. 2014. “Old Stones’ Song: Use-wear Experiments and Analysis of the Oldowan Quartz and Quartzite Assemblage from Kanjera South (Kenya).” Journal of Human Evolution 72: 10–25.

Roche, Helene, Robert J. Blumenschine, and John J. Shea. 2009. “Origins and Adaptations of Early Homo: What Archeology Tells Us.” In The First Humans: Origin and Early Evolution of the Genus Homo, edited by Frederick E. Grine, John G. Fleagle, and Richard E. Leakey, 135-147. New York: Springer.

Ruff, Christopher. 2009. “Relative Limb Strength and Locomotion in Homo habilis.” American Journal of Physical Anthropology 138 (1): 90–100.

Villmoare, Brian, William H. Kimbel, Chalachew Seyoum, Christopher J. Campisano, Erin N. DiMaggio, John Rowan, David R. Braun, J. Ramón Arrowsmith, and Kaye E. Reed. 2015. “Early Homo at 2.8 Ma From Ledi-Geraru, Afar, Ethiopia.” Science 347 (6228): 1352–1355.

Wood, Bernard. 2014. “Human Evolution: Fifty Years after Homo habilis.” Nature 508 (7494): 31–33.

Wood, Bernard, and Mark Collard. 1999. “The Changing Face of Genus Homo.” Evolutionary Anthropology 8 (6): 195–207.

FIGURE ATTRIBUTIONS

Figure \(\PageIndex{1}\) Homo habilis site map original to Explorations: An Open Invitation to Biological Anthropology by Chelsea Barron at GeoPlace, California State University, Chico is under a CC BY-NC 4.0 License.

Figure \(\PageIndex{2}\) Derivitive of  Homo habilis: OH 24 lateral right view; Homo habilis: KNM-ER 1813 lateral right view by eFossils is copyrighted and used for non-commercial purposes as outlined by eFossils; and, Homo habilis OH 7 Jaw by ©BoneClones is used by permission and available here under a CC BY-NC 4.0 License.

Figure \(\PageIndex{3}\)  Homo rudolfensis Cranium KNM-ER 1470 by ©BoneClones is used by permission and available here under a CC BY-NC 4.0 License.

Figure \(\PageIndex{4}\) Chopping tool by José-Manuel Benito Álvarez is used under a CC BY-SA 2.5 License.

TABLE ATTRIBUTIONS

Table \(\PageIndex{1}\) Homo habilis table original to Explorations: An Open Invitation to Biological Anthropology is under a CC BY-NC 4.0 License.

Table  \(\PageIndex{2}\) Summary features of Homo habilis original to Explorations: An Open Invitation to Biological Anthropology is under a CC BY-NC 4.0 License.