Early human ancestors sought out preferred tool components

The question of when our ancestors first began to use tools is an important one: it steers our view of how our brains were developing and the relationships our ancestors had with the environment and various potential food sources. And what Emma Finestone, Associate Curator at the Cleveland Museum of Natural History, has found in Kenya suggests that tool use was very much embedded in our behaviour by as early as 3 million years; she's shown that early hominins weren't just picking up and using handy bits of stone laying nearby - they were venturing for tens of kilometres to find the right sorts of stones to bring home and turn into tools, arguing that they very much knew what they were doing…

Emma - One big question is how did tool use begin and how important was it to the earliest tool users and tool makers? When we think about humans today, we're really dependent on our tool technology to solve adaptive problems and to access different food items. It's part of our life that we are really tied to. Everyone on earth uses tools. And the question when we think of 3 million years ago, 2.6 million years ago, is how important was tool use to those early tool makers and how were they making and using tools and integrating it into their daily lives and their movements across the landscape?

Chris - And what have we got to go on so far? When you look at the fossils we have and the remains we have and the things we've found, what sort of picture emerges before you come along with this current piece of research?

Emma - The earliest period of tool use, we know relatively little about because there are only a handful of archaeological sites that are older than 2 million years ago. What we do know is that hominins, which is a word that includes anyone in our family tree, were making and using tools and accessing food items. But what we don't know is how big this investment was and how far they were ranging for food resources and for tool resources. Non-human primates are known to use stone tools and can accidentally produce flakes that look like the same ones we find in the archaeological assemblage unintentionally, but they do it through a very opportunistic process where they have a food item and then they have stones that are available locally and they're just breaking apart a food item to access that food. The big question is in the earliest archaeological record, when we're talking about older than 2 million years ago, were hominins accessing food items in a similar way to non-human primates - where they're just cracking open a nut or maybe cutting something with an available stone nearby - or were they doing something more? Were they foraging for stones across the landscape and bringing them to places to process food?

Chris - Is that the key then? Is that what you've built your story around? The fact that if you've got evidence that someone is going and getting particular bits of stone because they make good tools, that's evidence that this must have been common practice at the time at which those individuals were active.

Emma - It's evidence that they were investing in tool behaviour because travelling a distance of several kilometres or 10 kilometres or more to get a specific type of rock, that takes a long time out of your day and that shows that that's really integrated into your foraging strategy if you're travelling to get stones, which in and of themselves have no caloric value to tool makers or to humans and their ancestors. So travelling to get stones shows that this is a behaviour that they're investing in and it's part of their foraging strategy from the onset of tool technology. And it also shows that they've already incorporated stone tools into their landscape patterns in their mental maps, which is a step beyond what we see in non-human primates. So it's an indicator of having mental maps and cognition to incorporate stone resources into their foraging routine and also an indicator that these hominins are foraging for stones as part of their foraging strategy, not just as an opportunistic one-off way to access a food item that they couldn't otherwise access.

Chris - And you've got evidence that this was happening.

Emma - Yeah, so at the site Nyanga, it's in Western Kenya and we've been working there since 2014. We have a stone tool assemblage between 2.6 and 3 million years old that has been made using both local but also non-local stone materials. We did a landscape-scale study where we were looking at which different materials are available throughout the landscape and which sources the hominins were accessing. And what we found is that the hominins were accessing not just local sources of stone, but they were accessing sources of stone that were 10 to 13 kilometres away from the Nyanga site, bringing them to the site and then processing food there using the stones that they obtained from further distances.

Chris - And you're comfortable that those stones didn't arrive where the hominins were by accident, that you're saying they brought them there and in fact, the environment somehow didn't. You're comfortable that this is active recovery of those stone pieces?

Emma - Yes, and how we know that, we first do analysis of where stones are available on the landscape from ancient riverbeds and from transport through rivers from primary sources to outcrops and riverbeds, which is where hominins are accessing the stone. So we surveyed ancient riverbeds to check what stones are available in which places. And then we also did a type of analysis that looks at the geochemistry, which is the trace elements of things in the rock that can link them to the sources on the landscape to check which sources are most similar to the artefacts that we have in the assemblage. And all of those indicators suggest that these stones were not locally available and that hominins travelled to get these stones and sometimes transported them directly to the site and flaked them on location.

Chris - So what's the take-home then? If you had to sort of write the newspaper headline, how would you sell this to a classroom full of eager palaeoanthropologists of the future?

Emma - I would sell it as stone tool behaviour was integrated into the daily life patterns of hominins 2.6 million years ago. We are a technologically dependent species. We rely on tool technology to survive and to access food. And it's likely that that has been happening for millions of years. Travelling that distance to obtain stone resources and foraging for stones with the same effort that hominins were foraging for food resources shows that this reliance on tool technology to survive, adapt, and to access different foods is what started off 2.6 million years ago and has continued today into being a key component of what makes us human.