A major change in the way stone tools were made

Around 1.7 to 1.6 million years ago, a new stone tool technology appears, spreads rapidly, and dominates the stone tool scene until about 300,000 years ago. This is the Acheulean stone tool industry and its characteristic tools—the hand axe and the stone flakes associated with it.

Prior to the Acheulean, hominins had made some very slow progress in their accumulation of stone flaking skills by starting to flake the core on both sides. We call this bifacial flaking, and the first assemblages with bifaces are in what Mary Leakey originally called the Developed Oldowan assemblages at Olduvai Gorge (“developed” because it had these new features of bifacial flaking). Bifacial flaking is important because, by flaking on both sides, the hominin has more options in the shaping of the stone tool. There is more control in the production of the final product.

Acheulean bifacial flaking—pieces are flaked off of each side of a cobble to form a cutting edge. Image credit Kaye Reed

What hominin made the Acheulean? There is widespread consensus that the earlier half of the Acheulean was made by Homo erectus. Eventually, probably around 500,000 years ago, a new hominin species is recognized—Homo heidelbergensis—that likely evolved out of H. erectus. There are also various differing opinions about the number and names of hominin taxa through this time period. For that reason, we will simply refer to them as “Acheulean hominins.”

The first Acheulean handaxes are rather crude in that they have been flaked maybe 10 to 15 times across each face, but they do have the shape that eventually becomes so distinctive—they are pointed at the end and broaden toward the base. Some are very large—two feet long—and some are tiny—just six inches or less. The smaller to medium size fit in the hand comfortably. They are even more comfortable if the sharp sides at the base are covered in resins (tree sap) or held in leather. They can be used for many different tasks.

Achuelean hand ax. Image credit Kaye Reed

Experimental work shows that they can be effective in butchering animals, cutting and stripping wood, processing plants, and digging. They can be a formidable weapon. This multiplicity of potential function has gained them the name the “Swiss-army knife of the stone age.” Research focused on the edge damage suggests that some of the younger in age, more regularly shaped hand axes, may have been mounted in slots and formed a hatchet-like tool. Some hand axes were made so they had a long broad cutting edge as opposed to a point—these are called cleavers. Both hand axes and cleavers are an excellent source of flakes, which makes them into a core. So, if you needed a flake with a fresh sharp edge, you could just knock one off on the fly (being careful not to destroy your hand axe).

In modern times, technology changes at a very fast pace, surging forward quickly often in synchrony across the world. It is inconceivable to us that technology does not charge forward with improvement every year. Not for the Acheulean. Technological change, at least in stone tools, changed at glacial speeds, so 100s of thousands of years saw no change at all. Measurable changes spanned half a million years. If we look at hand axes that date to 500,000 years ago, we may see some clear changes from the earlier periods. The hand axes are sometimes thinner, the edges are straighter, and they are made seemingly to a more regular pattern. Many flakes are removed to shape the hand axe. These display great skill, but not much in the way of innovation.

The Acheulean spanned an enormous time, and its spatial extent is equally impressive—from the tip of southern Africa, all across Africa, and spread across most of Eurasia.  Hand axes were made on the raw materials found in each region—quartzite in southern Africa, obsidian in East Africa, flint in the Middle East and Europe, and so on. Most of the raw materials were easily accessible and local—rarely were raw materials exploited from more than 20 kilometers away. This suggests that there was little or no exchange of raw materials and perhaps also that the stone tools were made and used and discarded rather close to their point of manufacture.

Did Acheulean hominins make and use tools on other raw materials? Remember that time and preservation is a challenge—only under extraordinary circumstances will any organic materials survive from Acheulean times. There are Acheulean sites with good preservation of bone and those that shaped bone tools are absent, though there are some signs that bone was sometimes used as a tool without shaping it. This signals that perhaps bone tool technology had not developed. However, there are a few sites that preserve wood, due to really special preservation conditions. These sites show us that hominins near the end of the Acheulean made tools out of wood, even spears.

At around 960,000 years ago there is excellent evidence for the regular use of fire by Acheulean hominins. There are glimmers of evidence earlier than this, but so far it is inconclusive. That being said, we expect that a hominin who has ventured into colder environments would have controlled use of fire. The tool kit of an Acheulean hominin was the hand axe, stone tool flakes, probably wooden tools, and fire.

A variety of Acheulean tools. Image credit Proceedings of the National Academy of Sciences (https://www.pnas.org).

What was an Acheulean hominin society like?

Acheulean hominins continue the prior Oldowan pattern of having numerous sites that suggest repeated visits by groups, so we can think of these as residential sites or campsites. They had fire that could be used to deter predators, cook food, and light the night for fireside chats. Their stone tool raw materials come from a more diverse set of sources than in the Oldowan, and also from more distant locations, being found outside the zones of rivers and streams and sometimes being as far as 10 kilometers from where they were discarded, but not more than 30 kilometers. This lack of long distant transport is not what we expect from tribal societies—these societies normally exchange materials across longer distances, sometimes hundreds or even thousands of kilometers. For this reason, it seems likely that Acheulean hominins retained the single-level society inherited from the last common ancestor.

Acheulean hominins were heavily muscled suggesting they were very strong and rugged. Their anatomy suggests that their life history patterns were not quite modern in that their young matured quickly, and this shortens that critical time when modern human youngsters are learning so much. This may explain the relatively slow nature of cultural change during the Acheulean—while the hominins were a technological species, their capacity for complex culture may have been modest. There is very little evidence for symbolic activity, but there are some odd patterns that have been interested as signaling a belief in the afterlife. For example, at the site of Atapuerca, the excavators interpret the large number of hominins there as having been ritualistically tossed down a hole. Beyond that, we have no figurines or ornaments or clearly worked ochre, so there is little evidence for the rich symbolic and ritualistic behavior that characterizes modern humans.

What did these Acheulean hominins eat and how did they get it?

As with the Oldowan, the remains of animals and organic materials rarely preserve at Acheulean sites, but there are exceptions. Some sites have large numbers of faunal remains, and at these, the remains of a diversity of animals are present, from small antelope up to very large mammals as large as elephants. Cut marks and hammerstone percussion marks are common at these sites, and the remains are consistent with butchery by the hominins.

The hominins that made the Acheulean left Africa and its tropical environments and ventured much further out into regions that must have had a cold season. These temperate climate environments lack plants foods, normally late fall through early spring, so animal foods would have been the only option. This, plus the evidence we have from butchery, has led paleoanthropologists to think that Acheulean hominins were effective and regular hunters of a diversity of prey. There is now a consensus that the “human predatory pattern” or HPP was in place with the earlier phases of the Acheulean.

Organics are rare as well, but in some cases microscopic remains of plant materials have been found on the tools of Acheulean hominins, as well as in their sites. These remains suggest a diverse plant diet that is what would be expected from a human diet in these environments. However, there is no evidence that they regularly ate coastal foods or riverine/lake foods. These hominins had the HPP and ate a diversity of plant foods, so in that way they resemble a modern terrestrial hunter-gatherer. But they had not yet broken into the aquatic food chain in a meaningful manner.

Written by Curtis Marean PhD

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