Creating stone tools was a key leap forward for our ancestors. It was so significant that scientists once thought it heralded the arrival of modern(ish) humans. But since then we've found much older stone tools, including some recently discovered stone tools that were made more than three million years ago. Will these be the oldest stone tools ever found? Or maybe there's a chance we'll find even older tools. How old could the oldest stone tools be?
Now this might seem like an impossible question to answer. How can we identify the age of something we haven't found yet? Well, chimps - our closest living relatives - don't make stone tools in the wild. Nor does any other ape. This would suggest that something unique happened during our evolution that made the creation of stone tools possible. If we can pinpoint when this change happened then we can narrow down when the oldest stone tools may have been made.
What do you need to make a stone tool?
In order to be able to make stone tools you need two things. Also stones, you need them too.
The first is one of those big fancy brains. You need to be smart enough to figure out which rocks make good tools, which rocks you can use to shape those tools, what sort of tool you need to make. The list goes on and on. Now, all of this might seem pretty trivial. Yet it's worth remembering it can take some monkeys years to figure out how to use rocks as tools. Not make tools with stones, but simply figure out they can pick up a rock and use it to smash stuff.
The other thing you need is the ability to pick up and make the rocks in the first place. Even creating the simplest stone tools requires being able to strike the stone at just the right angle to make flakes. As someone whose tried to do this, I can tell you that this is very challenging. Our hand likely needed to undergo some evolution before this was possible.
So, by figuring out when our ancestors became smart and handy we can help narrow down when they could have made the oldest stone tools.
Smartie-pants chimps
Humans are smart. Like, super smart. It's perhaps our biggest advantage in the evolutionary arms race. So you'd expect that this was one of the key changes that enabled us to make fancy stone tools. Except it doesn't seem to be the case.
Sure, you need to be smart to make stone tools but it looks like chimps are already smart enough. By extension, our ancestors with chimp-like brains were probably smart enough as well. Thus we can't look for increases in brain size to infer when they were making the oldest stone tools.
It turns out that whilst chimps don't make stone tools in the wild, they still have the capacity to make them. They just need us to teach them. Experiments on chimps have captivity have revealed they learn the nuances of tool creation very well. Which raises the question: why don't they make them in the wild?
Well, it turns out that their hands let them down. Chimps have very long fingers, to help them hook onto and climb trees. But this makes them a bit clumsy when it comes to precisely hitting rocks together. As such, whilst they can be taught to make tools with their hands they aren't that good at it. Instead they prefer to throw rocks at concrete, using the force to crack them as needed. The absence of concrete in the jungle is likely a big limiting factor on chimp technology.
Handy sign of the oldest stone tools
So hands seem to be the key to figuring out the age of the oldest stone tools. When did we begin to evolve these lovely, short fingered beauties? Millions and millions of years ago! Scientists have found evidence of improving dexterity in Australopithecus afarensis and Australopithecus africanus. These two closely related (and closely spelled) species are some of our oldest ape-like relatives. They lived from ~2 - 4 million years ago. Our family only emerged a few million years before them (~7 mya) and the oldest known stone tools are ~3 million years old.
Unfortunately hand bones are some of the smallest in the body. As such they're also the most likely to be lost and damaged, so the picture is still very incomplete. We can't say for sure whether they did have the dexterity to make stone tools. However, the increase in dexterity is noteworthy, so it seems plausible.
In other words, it looks like the oldest stone tools may well be almost a million years older than the oldest stone tools we've currently found.
References
Ambrose, S. H. (2001). Paleolithic technology and human evolution. Science, 291(5509), 1748-1753.
Boyd and Silk, 2012. How Humans Evolved
Harmand, S., Lewis, J. E., Feibel, C. S., Lepre, C. J., Prat, S., Lenoble, A., ... & Roche, H. (2015). 3.3-million-year-old stone tools from Lomekwi 3, West Turkana, Kenya. Nature, 521(7552), 310-315.
Schick, K. D., Toth, N., Garufi, G., Savage-Rumbaugh, E. S., Rumbaugh, D., & Sevcik, R. (1999). Continuing investigations into the stone tool-making and tool-using capabilities of a bonobo (Pan paniscus). Journal of Archaeological Science, 26(7), 821-832.
Skinner, M. M., Stephens, N. B., Tsegai, Z. J., Foote, A. C., Nguyen, N. H., Gross, T., ... & Kivell, T. L. (2015). Human-like hand use in Australopithecus africanus. Science, 347(6220), 395-399.
