One of the earliest species to be classified as human, designated as Homo habilis, appeared in Africa over two million years ago. While similar in many physical features to the earlier Australopithecines, Homo habilis exhibited significant behavioral changes.
The transition from the earlier bipedal australopithecines to hominines began sometime around 2.5 to 1.8 million years ago. Terrance Deacon, in a chapter in The Epic of Evolution: Science and Religion in Dialogue, writes:
“This transition took place over a half-million-year period and exhibits features that show this transition to be associated with significant cognitive changes: an increase in brain size and the introduction of stone tools.”
The emergence of the first humans is marked by some important anatomical and behavioral changes. There is a significant enlargement of the brain, in both absolute and relative size, from that found in the earlier australopithecines.The skull is round and lacks a snout. The brain size, which averages about 610 cc, is about 30% larger than the australopithecines.
In looking at the possibility of social changes as well as anatomical changes, Christopher Seddon, in his book Humans: From the Beginning, asks:
“Could the increased brain size of Homo habilis have been associated with such increased social complexity and enabled it to live in larger groups?”
Research has shown that there is a close relationship between the complexity of a primate’s social group and the size of its neocortex. In his book The Neanderthal’s Necklace: In Search of the First Thinkers, Juan Luis Arsuaga writes:
“The growth of Homo habilis’ neocortex should thus be seen as a social phenomenon.”
Juan Luis Arsuaga goes on to say:
“Their unusual social activity may well have been the key to their ecological success, and later to the success of our species as well.”
With regard to the ecological niche inhabited by Homo habilis, Juan Luis Arsuaga also reports:
“Homo habilis also differed ecologically from earlier hominids. It was the first species not completely tied to a forest environment, be it the rain forest like Ardipithecus ramidus or the drier and less dense forests inhabited by the Australopithecines. Homo habilis seems to have inhabited much more open territory, like savannahs with trees and low vegetation either well dispersed or clustered between large expanses of grassland. This ecological change was of critical importance, because it opened the door to even greater changes that came later, changes that allowed the descendants of Homo habilis to live in every conceivable region, climate, and ecosystem.”
Anatomically, there is also a reduction in the robustness of the teeth and jaws which is generally assumed to indicate a major change in diet, perhaps the consumption of more meat. The shape of the teeth falls outside of the range of the earlier australopithecines and are much closer to the later Homos (there were several later Homo species, including erectus and heidelbergensis.)
The discovery of a partial skeleton in 1986, OH 62, suggests that Homo habilis had an ape-like body-build with arms that were relatively long compared to the legs. In their book From Lucy to Language, Donald Johanson and Blake Edgar write:
“It was previously thought that in H. habilis, body proportions would be more modern. The implication was clear: this specimen, OH 62, had limb proportions reminiscent of the primitive condition seen in A. afarensis (Lucy).”
And finally, with regard to anatomy, there is a reduction of sexual dimorphism (sexual dimorphism is seen in animal populations where males are significantly larger than females, often more than twice the size of females). The change in sexual dimorphism is seen by some researchers as signaling a change in social organization away from a group in which a single dominant male controls a harem of females to one in which males may cooperate with each other.
The most significant behavioral change is seen in the use and making of stone tools. Many see this indicating a change in cognition and as a new way of adapting to the environment. In fact, one of the defining characteristics of Homo is generally considered to be the making and using of tools. While there are some chipped stone tools dated to 2.5 to 2.0 million years ago which are presumed to be associated with Homo habilis, tools dated to 1.7 to 1.8 million years ago are clearly associated with this species.
These earliest tools are generally classified as the Oldowan tool complex which is composed of fairly simple stone tools made from basalt, quartz, and quartzite. Thomas Wynn, in his chapter in the Handbook of Human Symbolic Evolution, writes:
“It is doubtful that there were any design criteria whatsoever, beyond perhaps big and little.”
Thomas Wynn goes on to say:
“Oldowan tools do not represent a qualitative leap in technology.”
With regard to the importance of tool use and toolmaking in defining our species, Carl Zimmer, in his book Smithsonian Intimate Guide to Human Origins, writes:
“Tools help define us as a species. We may not be the only species to make them, but no other species makes them as well as we do, or depends on them as much.”
Chris Stringer and Peter Andrews, in their book The Complete World of Human Evolution, write:
“…in behavior, humans are characterized by great complexity compared with other animals, and one of our special features is our great reliance on toolmaking and tool-using.”
There are some scholars who feel that toolmaking, particularly the making of complex tools, may be evidence of language.”
With regard to toolmaking as indirect evidence of language, researchers often point to a number of things. The fine motor control of the hands and fingers, needed to shape the tools, is controlled by Broca’s region in the brain, the same area that controls the motor movements for speech. Making stone tools requires planning, which is associated with language. And finally, toolmaking is a learned skill which may require language.
While stone tools may seem simple, they are not. Making stone tools requires a mental capacity and a way of thinking that is not found in other primates. Ian Tattersall, in his chapter in The Epic of Evolution: Science and Religion in Dialogue, writes:
“With the invention of stone tools, we have the first unequivocal evidence that hominids had moved cognitively well beyond the ape league, whatever they looked like.”
Not all stone breaks in such a fashion that it will produce a usable, sharp cutting edge. Stone that does produce this type of edge is not uniformly distributed geographically. This meant that Homo habilis, and the many toolmaking human species that followed, had to be able to recognize the right kind of stone, shape the tool, and then carry it to the place where it would be used. Ian Tatterstall puts it this way:
“We know that the earliest Homo anticipated needing the tools they would make, for we have evidence that they carried suitable stones around with them for long distances before making them into tools as needed.”
With regard to transporting tools and the material butchered by the tools, Thomas Suddendorf, in his book The Gap: The Science of What Separates Us from Other Animals, writes:
“Butchering sites show that Homo habilis transported objects sometimes several kilometers from their source; it is possible they also carried tools on their person to be ready for future use.”
In other words, with stone tools we see evidence of a new kind of thinking which involves planning for the future.
It should be pointed out that while the Oldowan tools are often found in association with the butchered remains of large mammals, there is no indication that Homo habilis actually killed the animals. It is most likely that they scavenged dead animals, bringing them to a site where they could then use their stone tools to butcher the carcasses.
Thomas Wynn writes of the intelligence required to make Oldowan stone tools:
“Oldowan tools did not require a particularly sophisticated intelligence.”
Thomas Wynn also writes:
“The Oldowan tools require only very simple spatial concepts such as proximity and order.”
Anatomically, Homo habilis was relatively small: the males stood about five feet tall and probably weighed about 100 pounds. While modern humans have an average brain size of about 1,350 cc, Homo habilis had an average brain of less than half of this size: 650 cc. The brain shape tends to be human.
The shape of the Homo habilis brain provides some interesting clues. In modern humans, one of the regions of the brain which is associated with language is Broca’s Region. Some researchers claim that language started with Homo habilis, based on the latex cast of the inside of a Homo habilis skull which shows Broca’s Region. One of the first scientists to examine this endocast was Ralph Holloway who writes in his chapter in the Handbook of Human Symbolic Evolution:
“…I was then of the opinion that the endocast showed a human third inferior frontal convolution, with a good example of Broca’s area.”
Ralph Holloway goes on to report:
“Unfortunately, later hominid endocasts from H. habilis to the present seldom show the sulcal and gyral patterns faithfully. It thus becomes impossible to test whether or not there had been further cortical reorganization from H. habilis times to the present, for instance in either Broca’s or Wernicke’s areas.”
Stone toolmaking required not only a brain which could visualize the tool and plan for its use, but also hands with a precision grip to fashion the tools. The toolmaking hand requires an opposable thumb. In his book Thumbs, Toes, and Tears and Other Traits that Make Us Human, Chip Walter writes:
“Habilis’s thumb had evolved to the point where it made toolmaking possible. Because of its distinctly human shape and mechanics, Homo habilis could do something never before seen in the natural world: cup its strong palms and fingers around an odd and irregularly shaped chunk of fling rock, grab another smaller stone the way you might grasp a baseball (two fingers on top and the thumb below in a grip known as the ‘three-jawed chuck’), and repeatedly but precisely whack the larger stone.”
Chip Walter goes on to say:
“In Homo habilis, evolution had shaped a hand that was the anatomical equivalent of a jack-of-all-trades. It could hold, twist, turn, push, and pull unlike anything that had come down the evolutionary pike.”
While Homo habilis used stone tools for butchering and processing dead animals, in all likelihood, Homo habilis was not the one who killed the animals. At the present time, the scarce data that we have about Homo habilis suggests a life-style based partially on scavenging the remains of big game killed by other predators. With an ability to plan, as well as sharp stone tools, Homo habilis could move into a kill site, quickly butcher some choice cuts of meat left behind by lions and other predators, and then retreat to a safe area to consume the meat and to crack open the bones with stone hammers to get at the nutritious marrow.
With regard to evidence for language and religion in Homo habilis, we see none of the symbolism, such as deliberate burials, which are generally associated with religion. With regard to language, there are some paleoanthropologists who feel that Homo habilis may have had language, or perhaps a proto-language, or perhaps the capability for language. In his book The Language Instinct: How the Mind Creates Language, Steven Pinker writes:
“Homo habilis, which lived about 2.5 to 2 million years ago, left behind caches of stone tools that may have been home bases or local butchering stations; in either case they suggest some degree of cooperation and acquired technology. Habilis was also considerate enough to have left us some of their skulls, which bear faint imprints of the wrinkle patterns of their brains. Broca’s area is large and prominent enough to be visible, as are the supramarginal and angular gyri…and these areas are larger in the left hemisphere.”
As a final note, there are a couple of cautions. First, there are some paleontologists who do not feel that habilis should be considered as a part of Homo but would prefer to classify this species as Austrolopithecus habilis. Lee Berger with Brett Hilton-Barber, in their book In the Footsteps of Eve: The Mystery of Human Origins, write:
“There remains some debate as to whether habilis should be classified as its own species at all, or whether it actually is an advanced australopithecine.”
These scientists feel that the habilis fossils have more similarity to the earlier australopithecines than with the later Homo species.
Second, while there are many who feel that Homo habilis is ancestral to modern humans, there are also many who feel that it was an evolutionary dead end.
Human origins
Human Origins: The Sounds of Language
Human Origins: Eyes
Human Origins: Making Spoken Language Possible
Human Origins: Fossil Evidence
Human Origins: Humans as naked apes
Human Origins: Sex
Human Origins: Menopause
Human Origins: Bipedalism