Compared with modern Homo sapiens, which have only been around for the last 200,000 years, Homo erectus, or "upright man," had a long reign. The ancient ancestor of modern humans lived from 2 million years ago till about 100,000 years ago, possibly even 50,000 years ago.
Fossils of H. erectus also show that the species lived in numerous locales across the globe, including South Africa, Kenya, Spain, China, and Java (Indonesia).
"Homo erectus spanned a large [temporal] and geographic range," said Adam Van Arsdale, an anthropologist at Wellesley College in Massachusetts, explaining the significance of H. erectus. "It is also important because it's the first fossil ancestral to modern humans that, in many ways, shares a lot of its ecology."
In particular, H. erectus had a similar range of body sizes to modern humans, and it is the first human ancestor to have similar limb and torso proportions to those seen in modern humans. This suggests it had adapted to walking on two feet in a more open, grassland environment, rather than swinging from tree branch to branch.
"Unlike Australopithecus fossils, Homo erectus fossils don't preserve features related to climbing," Van Arsdale told Live Science. And similar to modern humans, H. erectus used tools, technology and culture to hunt for and gather food, he said.
Anatomy and behavior
Homo erectus was taller than earlier human ancestors.
For instance, one of the most complete fossil skeletons ever found, a 1.5-million-year-old specimen of an adolescent male known as Turkana Boy (now known as Nariokotome Boy), may have grown up to 6 feet 1 inches (1.85 meters) tall as an adult, though other estimates put his maximum height at the more modest 5 feet 4 inches (1.63 m), according to a 2010 study in the Journal of Human Evolution. By comparison, the iconic 3.2-million-year-old Australopithecus skeleton dubbed Lucy was just 3 feet 7 inches (1.1 meters) tall at death, according to a 1988 reconstruction published in the American Journal of Physical Anthropology.
Homo erectus also had more variation in height — with more tall and short individuals — than more primitive humans.
Notably, some H. erectus individuals also had much larger brains than older hominins, according to a 2013 overview of H. erectus that Van Arsdale published in the Nature Education Knowledge Project. Specifically, small-bodied, early H. erectus fossils have brain sizes not much bigger than Australopithecus (an ancestor of the Homo genus), but the Nariokotome Boy and other early large-bodied specimens have a brain volume more than 50 percent larger than Australopithecus and about 60 percent the volume of people living today.
Those bigger brains and bodies required more food and energy to survive. Analyses on the dental micro-wear and stable isotope chemistry of H. erectus fossils (molecules from foodstuff naturally become incorporated into growing teeth and bones) suggest the ancient man ate a fairly flexible and diverse diet, which likely included a lot of animal protein, according to a 2011 review of hominin diets published in the journal Science.
Homo erectus' larger brain may explain why its apparent intelligence and why it displays so many distinctly human behaviors. In terms of intelligence, "I don’t think [H. erectus] would be great elementary school students if we try to put them through our education system," Van Arsdale said. "But they were very successful in a lot of different environments."
For example, a study published in 2011 in the journal Proceedings of the National Academy of Sciences (PNAS) suggests H. erectus (and potentially other, earlier Homo species) may have harnessed fire to cook food as early as 1.9 million years ago. A 2013 analysis of ancient tools (stone hand axes), also published in PNAS, reveal the human ancestor was butchering animals by at least 1.75 million years ago.
And in 2014, researchers discovered 540,000-year-old shell carvings — the oldest engravings ever found — belonging to H. erectus, as well as shells that were apparently used as tools. Many of the shells discovered at the Java site contained unnatural holes near the shells' hinges, exactly at the point where muscle keeps the shell closed. This suggests H. erectus may have purposely drilled these holes to easily open the shells and eat the mollusks, before using the shells as tools and canvasses, according to the study published in Nature.
Homo erectus' ability to make complex tools was possible because of the strength and dexterity in its hands, which it owes to a certain hand-bone projection called a "styloid process" that was previously thought to only exist in Neanderthals and modern humans, according to a 2013 PNAS study.
The lineage and evolutionary history of H. erectus and other Homo species is unclear, and has been muddied further by recent finds.
Homo erectus was once thought to have first evolved from an earlier human ancestor, known as Homo habilis, somewhere in East Africa. It was thought that H. erectus then spread out to inhabit South Africa, parts of Europe (Spain and Italy), the Caucasus, India, China, and Indonesia.
However, there's much disagreement about whether these populations are actually all H. erectus, or if they should be considered other species. According to Van Arsdale's H. erectus review, some experts argue H. erectus is restricted largely to Eastern and Southeast Asia, some fossils from Western Asia and Africa should be considered Homo ergaster and European remains are best described as Homo heidelbergensis.
Confusing matters more, after analyzing a new skull — called Skull 5 — in 2013, researchers made the controversial argument in the journal Science that various contemporary Homo species, including Homo rudolfensis, Homo habilis and possibly Homo ergaster, were actually Homo erectus.
Scientists also don't agree on whether H. erectus is a direct human ancestor to Homo sapiens. "I would put it as an ancestral to living humans," Van Arsdale said. "That doesn't mean that every fossil is an ancestor to humans, but the species as a whole is."
Other notable fossils
The first H. erectus fossil found was a 1-million-year-old skull discovered by Dutch surgeon Eugene Dubois in Indonesia in 1891.
Other notable fossils include the 1.77-million-year-old skull of an elderly man, discovered in Dmanisi, Georgia. The man had lost most of his teeth long before he died, causing much of his jaw to deteriorate, according to the Smithsonian Institution. This leads researchers to believe that other members of the man's social group must have cared for him, one of the first examples of such compassionate social behavior in a human ancestor.
Other H. erectus fossils have been found in Olduvai Gorge, Tanzania, where anthropologists have discovered primate and early human ancestor fossils going back almost 25 million years.
- Smithsonian: What Does It Mean to Be Human?
- Science: A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early Homo.
- Nature: Homo erectus — A Bigger, Smarter, Faster Hominin Lineage