# The Genus Homo and the Emergence of Us

## Tools and Brains: Homo habilis, Homo ergaster, and Homo erectus


### Learning Objectives

By the end of this section, you will be able to:
1. Compare and contrast the anatomy and material culture of H. habilis, H. erectus, and H. ergaster.
2. Define the term “tool industry” and describe the tools typified by the Oldowan and Acheulean industries.
3. Identify possible correlations between the environment, diet, new behaviors, and brain growth.

### The Toolmakers

Archeologists use the word industry to describe a classification or assemblage of stone tools. The Oldowan tool industry is the oldest known stone tool industry. It dates from around 2.5 to 1.5 MYA. Because there were several hominins in Africa during this time, it is unclear whether these tools were created and used by H. habilis or by Paranthropus boisei, or by both (Susman 1991). Oldowan tools are fairly crude and primitive in appearance, which can make it difficult to find and identify them in the field.
Mary Leakey was the first to create a system to classify Oldowan assemblages, basing her classification on utility, or how the tools were used. Later efforts were made to classify tools based on how the tools were made. All Oldowan tools were created by using hard hammer percussion, in which flakes are chipped away from a stone, resulting in a “core”. These cores served as basic tool that could have been used for killing game, cutting meat and plants, and possibly woodworking. Oldowan toolmaking is the earliest evidence of “flint knapping,” a technique that became more complex over time, resulting in more sophisticated tools ().
Handedness, or brain lateralization (i.e., whether one is right-handed or left-handed), is a cognitive development that can be inferred through evidence of the use of a dominant hand in creating and using tools. The use of a dominant hand suggests a possible reorganization of the brain. It is believed that about 90 percent of humans are right-handed, which differs from apes, which are closer to 50 percent. David Frayer (2016), an anthropologist from the University of Kansas, has concluded that the brain lateralization of Homo habilis was more like that of modern human than that of apes. Frayer found striations on the teeth of a 1.8-million-year-old Homo habilis fossil that indicate right-handedness. He concluded that meat was pinched between the teeth and held in place with the left hand, while the right hand cut the meat with a tool. Brain lateralization, increasing brain size, and tool use are just some of the key developments we see in the genus Homo.

### Homo ergaster

 is the first Homo that looks much like H. sapiens. A key difference between H. ergaster and earlier hominins is that H. ergaster exhibits substantially less sexual dimorphism in body size. H. ergaster males were only 20 percent larger than females. Likewise, modern human males are only 15 percent larger than females. This contrasts sharply with all other previous hominins, such as the australopithecines, in which males were 50 percent larger than females. It is well established that in mammals, significant dimorphism is associated with polygyny, and a lack of dimorphism is associated with a monogamous mating system. It has been suggested that the reduction in dimorphism seen in H. ergaster may indicate less male-male competition for access to females and perhaps a shift toward a monogamous mating system, with substantial parental investment in offspring.
Other similarities between H. ergaster and modern humans are seen in the teeth and postcranial features. The average cranial capacity of H. ergaster is 1,100 cc, which is just a bit smaller than that of modern humans, who average 1,400 cc. There is a very important specimen of H. ergaster that bears mentioning, the Nariokotome Boy. This specimen was discovered in 1984 by Kenyan paleontologist Kamoya Kimeu near Lake Turkana in Kenya. It is dated to approximately 1.6 MYA. The specimen is believed to represent a boy of about 12 years old, determined by various dental and cranial features. He was about 5 feet 4 inches tall, roughly the same height as a modern boy of the same age (). It has been estimated that his adult height would be around 5 feet 10 inches, with an estimated cranial capacity of 900 cc. The Nariokotome Boy looks tremendously modern in appearance despite being 1.6 million years old.

### Homo ergaster Technology

Homo ergaster continued to use Oldowan stone tools, but they also began to construct much more complex tools, referred to as the Acheulean industry (). These tools have been found throughout Africa, Europe, and the Middle East and are first noted as appearing approximately 1.6 MYA to 200,000 years ago. These types of tools are rarely found in Asia. It is currently unclear whether this is because the Acheulean industry had not yet been developed when H. erectus migrated to Asia or because bamboo (a plant found in abundance in Asia) was found to be a more versatile resource than stone. As wood and bamboo are biodegradable, no remains of tools constructed from these materials would exist today.
Unlike Oldowan tools, Acheulean tools actually look like tools. Acheulean tools are distinct from Oldowan tools in that they were modified on both sides, resulting in a symmetrical tool with two faces, also known as biface. One end of the tool was tapered, while the other end was rounded. The creation of symmetrical objects from stone materials is believed to represent an increase in cognitive ability as well as motor skills in the tool maker. These bifaces were struck from large flakes, which had themselves been struck from boulder cores. This required a more delicate technique than banging one rock into another. Acheulean tools were typically created used the soft hammer technique. In this technique, hard rock such as flint is chipped by striking it with a softer material such as bone or wood. The gentler blows detach small flakes that leave smooth, shallow scars, creating a straighter and more uniform cutting edge.
The main advantage of Acheulean technology is that it allowed hominins to get a better grip on their tools, as they were shaped to fit the hand. This tool type was used primarily as a hunter’s knife but also for chopping, scraping, and even piercing. The most common type of biface tool is a hand axe. Note that even though these tools are called axes, they are held in the palm of the hand. Another type of Acheulean biface used by Homo ergaster is called a cleaver (). The cleaver had a wide cutting edge across the end instead of a point and was best suited for hunting or hacking wood. Another Acheulean tool is the side scraper, used to scrape hides that could then be turned into simple clothing.

### Evidence of an Increase in Meat Eating

In 1973, a specimen of H. ergaster known as KNM ER 1808 was found in Koobi Fora, Kenya. Dated to about 1.7 MYA, this is the most complete H. ergaster specimen ever found. Analysis of KNM ER 1808 suggests that H. ergaster may have been eating carnivore liver, which is high in Vitamin A. This may indicate a dietary shift toward increased meat eating by H. ergaster.

### Homo erectus: A Success Story

 is the longest-surviving species in the genus Homo. For almost two million years, H. erectus existed and evolved. Also known as the “Upright Man” or Java Man, H. erectus was first found in Indonesia in 1891 by Eugene Dubois, a professor of anatomy at the University of Amsterdam. At a site called Trinil, he found a skull cap and a femur. He named the specimen Pithecanthropus erectus. The most current dates for Homo erectus are 1.2–1.6 million years ago. H. erectus exhibits a cranial capacity averaging 900 cc and several distinguishing characteristics. These characteristics include a slightly projecting nasal spine, shovel-shaped incisors, a nuchal crest (a ridge in the back of the skull that supported strong neck muscles), very thick skull bones, and pronounced brow ridges. They also had longer legs, evidence that they were utilizing energy much more efficiently when walking and becoming effective hunters. We also see a diminishing of the protruding jaw (or prognathism) that was so prominent in the australopithecines.
There is evidence that H. erectus was using fire around 1.7–2.0 MYA, which would make it the first or one of the first hominins to do so. Ancient hearths, charcoal, and charred animal bones have been found in Zhoukoudian, China. This evidence suggests that H. erectus was hunting, cooking, and eating meat. Also found at Zhoukoudian are a number of fossil skulls that were once thought to display evidence of cannibalism. However, recent research evidence suggests that the remains of these H. erectus were prey to animal scavengers such as hyenas (Boaz et al. 2004).
The Smithsonian Institution has created an interactive tool that visually illustrates the interrelationships between an increasingly variable and colder climate, encephalization, bipedalism, and new technologies and tool use. These correlations align with fossil evidence indicating changes in diet and caloric requirements in response to a colder and changing climate, which ultimately fueled a growing brain. The “expensive tissue hypothesis” proposes that maintaining a brain is metabolically expensive and that, in order to meet the energy requirements of a larger brain, our digestive system became smaller and shorter, making it more suited for higher-quality, nutrient-dense food such as meat (Aiello and Wheeler 1995). The list below summarizes some of the key evolutionary changes seen in H. erectus from 2 MYA to possibly as recent as 50,000 years ago, which provide further support for these correlations (Dorey 2020).
1. There is a progressive increase in brain size in H. erectus, from about 550 cc to 1,250 cc.
2. There is evidence of increased use of fire and of eating cooked meat at H. erectus sites. H. erectus would have needed as much as 35 percent more calories than previous hominins (Fuentes 2012).
3. The eating of softer foods as a result of cooking meat and plants alleviated the need for large chewing teeth and jaws. Over time teeth became smaller, which resulted in thicker enamel.
4. There is a gradual decrease in prognathism, and as in H. habilis, skulls provide evidence of smaller teeth and jaws, which would have made room for larger brains.
5. H. erectus is taller than any other previous hominin, with longer legs that provided the ability to run great distances and chase prey. New research is shedding some additional light on the possible benefits of running in early hominins The fossil evidence suggests that endurance running is a derived adaptation of the genus Homo, originating about two million years ago, and may have been instrumental in our evolution (Bramble and Lieberman 2004).

### The Homo ergaster and Homo erectus Debate

There is great debate as to whether Homo ergaster and Homo erectus are one species or two. Some refer to H. ergaster as the “early” H. erectus. Their differences are largely geographical: H. ergaster is associated with Africa and H. erectus with Asia. Yet some researchers have concluded that H. ergaster and even H. habilis should be referred to as H. erectus. Whether to lump or split the diverse species in the genus Homo is an ongoing challenge in the scientific community. While there are some anatomical differences between H. erectus and H. ergaster, they are fairly minimal.
The diversity and number of evolutionary changes seen in H. erectus indicate that H. erectus set the stage for the arrival of the archaic Homo, which we will cover in the next section.