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 (Figure 5.7). 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. Figure 5.7 This specimen of Homo ergaster is known as the Nariokotome Boy. It is believed to be the remains of a boy who was about 12 years old at the time of death. (credit: “Homo ergaster (fossil hominid) (Lower Pleistocene, 1.5 to 1.6 Ma; Nariokotome, Lake Turkana area, Kenya) 4” by James St. John/flickr, CC BY 2.0) 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 (Figure 5.8). 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. Figure 5.8 This hand axe, found in the Zamora province, Spain, displays the form and construction techniques typical of the Acheulean industry. (credit: Jose-Manuel Benito/Locutus Borg/Wikimedia Commons, Public Domain) 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 (Figure 5.9). 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. Figure 5.9 Map of Acheulean cleaver finds dated to the Lower Paleolithic (1.76–0.13 MYA). Note the concentration of artifacts found in certain areas of Africa and in Spain. (attribution: Copyright Rice University, OpenStax,under CC BY 4.0 license) 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.