5.2.3 Homo erectus : A Success Story

Homo erectus 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).