The possibilities in the design of rock tools were limited by the inflexibility and brittleness of the material. The design effort was constrained to the sizing of the tool to the intended task and the development of sharper, longer, and more usefully shaped cutting edges that always required backing to support them. In use, the bending and twisting of long knifelike tools had to be avoided lest the action destroy them; this would also have been true of chisels and gouges. Similarly, even the much later heavier tools, such as the ax and adz, required care in use.

The effectiveness of rock tools has been demonstrated from time to time by both archaeologists and modern workers unaccustomed to such tools. An experienced operator using a rock knife can skin a small animal about as quickly and deftly as he can using steel. When the rock tool is subjected to substantial forces, however, the worker must use caution, intelligence, and control. Care is required to avoid twisting or prying with a rock blade (knife or ax); a thin blade may snap, and a thick one may collect local nicks.

Eoliths

The first act of the drama of tools is hazy. There are what have been called eoliths, “tools from the dawn of the Stone Age.” Such stones with sharp fractures, found in great quantities in layers from the geological epochs before the Pleistocene, were once assumed to be tokens of human presence in the preceding Pliocene and even earlier Miocene epochs. These rocks, fractured by glacier pressure, wave action, or temperature change, are no longer taken as indexes of humans, although primitive peoples undoubtedly used them as ready-made objects before they deliberately started to fracture similar rocks in the late Pliocene. There are detailed criteria by which human-flaked and nature-flaked stones can be almost unerringly distinguished. Human origin is also evidenced by association with detached flakes and the stones that served as hammers.

The oldest known tools—consisting of primitive hammers, anvils, and cutting tools and dating to 3.3 million years ago—were discovered in 2011 and 2012 at the Lomekwi 3 site near Kenya’s Lake Turkana (Lake Rudolf). Tools found in 1969 at the Koobi Fora site, near Lake Turkana, consisted of five choppers, a number of flakes, and a couple of battered stones. The tools lay on the surface; the flakes were found three feet below them in tuff (volcanic rock) datable to about 2.6 million years ago. Artifacts known from Olduvai Gorge, Tanzania, included tools, as well as the jaw and teeth of a human who may have been the toolmaker. These items were found in the 1950s under tuff having a potassium-argon date of about 1.8 million years, a Lower Pleistocene age.

All of these tools are of a single type, a general-purpose implement that changed little in form during the next 2 million years. It is variously known as a pebble tool, pebble chopper, chopping tool, or simply as a chopper. Waterworn and hence rounded, up to about the size of a fist, the pebble, preferably flattish rather than spherical, was given a few violent but skillfully applied blows by a hammerstone. Several large flakes or chips were knocked off the rock to create on it a sharp and roughly serrated crest, or ridge, yielding an implement that was edged at one end and could be gripped at the opposite end. Rudimentary yet versatile, the chopper could be used to hack, mash, cut, grub roots, scrape, and break bones for their marrow.

Although the large sharp-edged flakes struck from the pebble were themselves useful for light cutting and scraping, it was not until perhaps 40,000 years ago that there was a development of flake tool industries in which preshaped flakes were purposefully detached from a core that was then discarded. But the Oldowan chopper and the struck-off flakes—the earliest generalized primitive tools—between them solved the problems of how to get through the skin of a slain animal, dismember it, and divide the meat.

The Acheulean industry

As the Pleistocene Epoch progressed, humans slowly developed the primitive chopper into a better instrument. About half a million years ago a superior implement finally appeared after nearly 2 million years of effort. The industry, or style, is known as the Acheulean, and the typical implement was the flint hand ax (sometimes called a fist hatchet). Throughout the ages the plump chopper and its bluntly angled crest had been streamlined by starting with a longer piece of rock and flaking the entire surface to produce an almond-shaped (amygdaloid) implement 20–25 cm (8–10 inches) long. This stone, much thinner than the chopper, was also sharper and more effective because the cutting edges were formed from the intersection of two curved and flaked surfaces (bifacial working).

This Acheulean hand ax was the product of evolution; certain of the intermediate stages, clearly leading to the typical and standardized form, have been identified as Chellean and Abbevillian. Despite the term ax, the tool was not hafted but was simply held in the hand. One end was tapered, the other rounded. The tapered end might be rather pointed or have a small straight edge. The tool was sharp for most of its periphery and seems to have been primarily a hunter’s knife but probably very useful, too, for other purposes, such as chopping, scraping, grubbing, and even piercing. Sharp, thin and symmetrical, light and elegant, it was quite different from the heavy chopper, with its rather blunt edge.

Another biface, the Acheulean cleaver, assumed prominence about 250,000 years later. A variant of the hand ax, it had a wide cutting edge across the end instead of a point and was better suited than the hand ax for hunting or hacking wood.

Neanderthals, excellent hunters and toolmakers, appeared on the scene at least 200,000 years ago, just ahead of the last glaciation but well within the Acheulean. Their tool kit was impressive for the wide variety of hand axes, borers, knives, and choppers it contained. The kit was novel for its scrapers and heavily serrated blades having a sawlike appearance, implements that were essential to the working of wood, bone, and horn into tools and weapons. The Neanderthals regularly used fire, and it is presumed that they could make it, although the direct evidence is missing. Fire was useful in tool manufacture, for charring the end of a stick not only helped shape the point by making it easier to scrape but also hardened it, as for a spear point. This fire hardening was probably the first human-manufactured modification of a natural property. Thoroughly wet wood, bent to shape and brought to dryness over the heat of a fire, would retain its bent form, a most useful property.