Oldowan Hominins

Humans are a cultural species reliant on tools. So, paleoanthropologists have always been interested in this basic research question—when did hominins become tool makers? Many primates make and use tools, so we anticipate that the shared common ancestor of hominins and other apes made tools. So, let’s sharpen that research question and ask this—when did hominins become regular users and makers of tools, thus setting them apart from their primate cousins? When did they make the formative departure from other primates to become a hominin dependent on tools?

All paleoanthropologists agree that at around 2.5 million years ago there is incontrovertible evidence that hominins flaked stone tools. But almost all paleoanthropologists agree that there must have been a preceding phase when tool use and manufacture was common but rather invisible to the scientists of human evolution.

Until recently, the earliest stone tools dated to 2.5 million years ago, while A. afarensis dates to around 3.4 million years ago. But in 2010, scientists published a result from Dikika in Ethiopia that was exciting but controversial. They described marks on the surfaces of 3.4-million-year-old bones that they interpret as being made by stone tools, including stone tool cutmarks and hammerstone percussion marks. They also speculated that these may have been from sharp stone flakes that were picked up off the ground, not intentionally flaked by early hominins, and thus represented a preflaking technology. This set off an exciting debate that pushed forward some rapid advances in methods for recognizing stone inflicted marks in an objective manner.

While scientists bashed away at this issue, a team working in Turkana, Kenya, at a locality called Lomekwi published another controversial report on stone tools that dated to a similar age of 3.4 million years ago. The stone tools there they argued were intentionally flaked, but flaked in ways that were somewhat more primitive than later-occurring widely accepted stone tools. There is still debate over these finds, with some researchers arguing that the stone tools derive from sediments younger than 3.4 million years ago.

But here we have, at 3.4 million years ago, a hand showing the hallmarks of tool use and production, controversial evidence for those tools. Scientists continue to test these important ideas.

By 2.5 million years ago, scientists agree that there is incontrovertible evidence that hominins were making stone tools and had gained control of what we call the knapping process through understanding conchoidal fracture. Knapping is the process of driving off flakes from one stone, what we call a core, by some other material such as a stone or a bone. Conchoidal fracture is when stone breaks apart in a relatively controlled manner by force propagating through the stone in the shape of a cone. Think rock thrown at a window, and the cone-shaped break it causes. Oldowan technology, named after the famous locality in Tanzania, shows an understanding of this process.

From 2.6 to about 1.7 million years ago, the stone tool record has variants of the Oldowan, but nothing in technology changes dramatically. The vast majority of Oldowan tools are made from cobbles that were collected from stream beds, and the evidence so far suggest that most of these cobbles were collected from places nearby, less than three kilometers away from where they were used and dropped, but there are some instances where the cobbles came from locations up to ten kilometers from where they were dropped. This suggests these early hominins did not carry tools around with them (curate) for long periods nor travel long distances deliberately to collect stone.

Who made the Oldowan tools? We know they were made by hominins, but which hominin is a puzzle. Most paleoanthropologists think one or more of the hominins from the “early Homo” group made the stone tools, but some also suggest that the robust australopithecines cannot be counted out. For this reason, we will call them “Oldowan hominins.”

Using the archaeological record to reconstruct ancient social behavior is very challenging, but we have some evidence that speaks to the way early hominins organized their lives. There are a series of sites from East Africa that show that early hominins used central places, what we might think of as camps. These sites have large numbers of stone tools and butchered bones, which are spatially clustered, and the number of items is so high that it cannot represent one visit—repeated use makes sense. The tools suggest that they transported raw materials to these locations, flaked the tools, and used them there.

Most of the raw materials used by the hominins from these sites were collected from nearby sources—normally three to five kilometers. So, they did not seem to travel far from these camps, at least to collect stone. We do not know how large their groups were, how far those groups ranged over the year, or other very important details. Importantly, most of these raw materials are cobbles from rivers and streams. This suggests that the early hominins were sticking to watered areas, perhaps because these are normally also riparian woodlands, and trees offer sanctuary from some predators.

Modern humans are reasonably unique among mammals in that they regularly prey on other animals far larger than them. Humans do this by using advanced weapons (projectiles, poisons, traps, etc.) to kill these large and dangerous prey. Because of this ability, many hunter-gatherer groups have diets where animal foods are a common, even predominant, component of the diet, and this again is unique among primates. We call this the “human predatory pattern,” or HPP for short. For this reason, the origins and evolution of the human predatory pattern has been a central research question for paleoanthropologists since its inception.

Meat is a high-quality resource due to its rich protein levels and many important nutrients. Modern taphonomic studies, which deal with the processes of fossilization, show us that there is one best way to attain meat in the wild and that is to be the killer of an animal. Animals that are killed are rapidly stripped of their flesh, so it is hard to attain lots of meat by being second in line (a scavenger), unless you can drive lions and hyena off their prey. Exceptions to this would be the death of very large prey, such as elephants, and there is good evidence that sabertooth cats, which were present at this time, focused predation on large prey.

Paleoanthropologists have long theorized that a key milestone in becoming human was when hominins began eating meat, and thus to get regular access to that meat, we think they must have been hunters. Since the brain is such a hungry organ and requires a lot of protein, many paleoanthropologists thought that the expansion of brain size and meat eating were inextricably linked. Since the oldest Oldowan tools date to 2.5 million years ago, close to the origin point of early Homo and the first evidence for brain expansion, paleoanthropologists thought for many years that these illustrated an evolutionary link—tools and meat and brains! But does it?

Recently, scientists have dissected this tools-meat-brain hypothesis. They point out that mammals have other equally important food types in their carcass, for example fat, which is rich in calories and mostly found within the bones in the form of marrow. To access this marrow, one either needs really strong jaws and big crushing teeth (like a hyena) or a hammerstone and the ability to hold that hammerstone and pound it on things (Lucy certainly had that ability). Importantly, African predators like lions and leopards have limited abilities to break open bones—they leave these for the bone crackers the hyenas or a hominin with a hammerstone. Hominins could get animal fats without being a hunter. Animal carcasses are a rich package of high-quality food, but researchers argue that it is better to think of these two foods, meat and marrow, as separate, and their addition to the hominin diet over time as staggered. Let’s do that.

Our ape cousins, the chimpanzees, have an eclectic diet that, while based in plants, includes substantial amounts of meat. Chimpanzees are well known to kill and eat small antelope and monkeys. This has led paleoanthropologists to theorize that the last shared common ancestor of chimps and hominins also ate some meat from small mammals and over time as hominins evolved separately from the chimpanzee lineage, they slowly evolved this pattern up to hunting and killing large mammals like wildebeest and buffalo. We can call this the “chimpanzee model” for the origins of the HPP. Researchers showed that this model has numerous flaws and no longer fits the evidence. They offer a new model that argues for this series of steps:

1. use of pounding tools all the way back to the shared common ancestor
2. movement onto more open habitats with the origins of bipedality and the expansion of these habitats
3. encounters with bones remaining from the kills of other carnivores
4. bashing of bones with pounding tools to access marrow (percussive scavenging)
5. modest occasional scraping of bits of flesh from these bones
6. beginnings of stone tool flaking to improve the ability to butcher meat and disarticulate bones
7. incremental hunting of animals and their butchery with these flaked tools.

How does this square with the evidence? The Dikika evidence along with the tool-using hand of Australopithecus afarensis are consistent with this new model. Several Oldowan-age archaeological sites have comingled stone tools and substantial numbers of fossil ungulates bones with stone tool cut marks and hammerstone percussion marks that broke open the bones. But scientists disagree as to whether these remains signal persistent active hunting or scavenging. More data and research are required. But at this stage we can say with confidence that during the Oldowan, hominins were making stone tools, using hammerstones to bash open bones for marrow, stripping at least small amounts of meat off bones, and maybe even feasting off whole carcasses. While there is little evidence, other forms of evidence such as isotopes show us that these hominis were eating large amounts of plant foods, but there is debate over exactly what these plants foods were.

Written by Curtis Marean PhD