Modern People Making Stone Age Tools


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The stone flakes are flying, but what brain regions are firing? Shelby S. Putt, CC BY-ND


Brain-imaging modern people making Stone Age tools hints at evolution of human intelligence


Shelby Putt, Indiana University


How did humans get to be so smart, and when did this happen? To untangle this question, we need to know more about the intelligence of our human ancestors who lived 1.8 million years ago. It was at this point in time that a new type of stone tool hit the scene and the human brain nearly doubled in size.

Some researchers have suggested that this more advanced technology, coupled with a bigger brain, implies a higher degree of intelligence and perhaps even the first signs of language. But all that remains from these ancient humans are fossils and stone tools. Without access to a time machine, it’s difficult to know just what cognitive features these early humans possessed, or if they were capable of language. Difficult – but not impossible.

Now, thanks to cutting-edge brain imaging technology, my interdisciplinary research team is learning just how intelligent our early tool-making ancestors were. By scanning the brains of modern humans today as they make the same kinds of tools that our very distant ancestors did, we are zeroing in on what kind of brainpower is necessary to complete these tool-making tasks.

A leap forward in stone tool technology

The stone tools that have survived in the archaeological record can tell us something about the intelligence of the people who made them. Even our earliest human ancestors were no dummies; there is evidence for stone tools as early as 3.3 million years ago, though they were probably making tools from perishable items even earlier.

As early as 2.6 million years ago, some small-bodied and small-brained human ancestors chipped small flakes off of larger stones to use their sharp cutting edges. These types of stone tools belong to what is known as the Oldowan industry, named after Olduvai Gorge in Tanzania, where remains of some of the earliest humans and their stone implements have been found.

The more basic Oldowan chopper (left) and the more advanced Acheulian handaxe (right). Shelby S. Putt, courtesy of the Stone Age Institute, CC BY-ND

Around 1.8 million years ago, also in East Africa, a new type of human emerged, one with a larger body, a larger brain and a new toolkit. This toolkit, called the Acheulian industry, consisted of shaped core tools that were made by removing flakes from stones in a more systematic manner, leading to a flat handaxe with sharp edges all the way around the tool.

Why was this novel Acheulian technology so important for our ancestors? At a time when the environment and food resources were somewhat unpredictable, early humans probably began to rely on technology more often to access food items that were more difficult to obtain than, say, low-hanging fruits. Meat, underground tubers, grubs and nuts may all have been on the menu. Those individuals with the better tools gained access to these energy-dense foods, and they and their offspring reaped the benefits.

One group of researchers has suggested that human language may have evolved by piggybacking on a preexisting brain network that was already being used for this kind of complex tool manufacture.

So were the Acheulian toolmakers smarter than any human relative that lived prior to 1.8 million years ago, and is this potentially the point in human evolution when language emerged? We used a neuroarchaeological approach to answer these questions.

Imaging brain activity now to reconstruct brain activity in the past

My research team, which consists of paleoanthropologists at the Stone Age Institute and the University of Iowa and neuroscientists at the University of East Anglia, recruited modern human beings – all we have at our disposal these days – whose brains we could image while they made Oldowan and Acheulian stone tools. Our volunteers were recreating the behaviors of early humans to make the same types of tools they made so long ago; we can assume that the areas of their modern human brains that light up when making these tools are the same areas that were activated in the distant past.

We used a brain imaging technology called functional near-infrared spectroscopy (fNIRS). It is unique among brain imaging techniques because it allows the person whose brain is being imaged to sit up and move her arms, unlike other techniques that do not allow any movement at all.

Participants in the study made stone tools while their brain activity was measured with fNIRS. Photo: Shelby S. Putt, CC BY-ND

Each of the subjects who participated in this study attended multiple training sessions to learn how to make Oldowan and Acheulian tools before going in for the final test – making tools while hooked up to the fNIRS system.

We needed to control for language in the design of our experiment to test the idea that language and tool-making share a common circuit in the brain. So we divided the participants into two groups: One learned to make stone tools via video with language instructions; the other group learned via the same videos, but with the audio muted, so without language.

If language and tool-making truly share a co-evolutionary relationship, then even those participants who were placed in the nonverbal group should still use language areas of the brain while making a stone tool. This is the result we should expect if language processing and stone tool production require the same neural circuitry in the brain.

During the neuroimaging session, we had the participants complete three tasks: a motor baseline task during which they struck two round stones together without attempting to make flakes; an Oldowan task that involved making simple flakes without trying to shape the core; and an Acheulian task where they attempted to shape the core into a handaxe through a more advanced flake removal procedure.

Training video shown to participants. The verbal group heard the instructor’s voiced instructions, while the nonverbal group watched a muted version.

The evolution of human-like cognition

What we found was that only the participants who learned to make stone tools with language instruction used language processing areas of the brain. This probably means that they were recalling verbal instructions they’d heard during their training sessions. That explains why earlier studies that did not control for language instruction in their experiment design found that stone tool production activates language processing areas of the brain. Those language areas lit up not because of anything intrinsic to making stone tools, but because while participants worked on the tools they also were likely playing back in their minds the language-based instruction they’d received.

Our study showed that people could make stone tools without activating language-related brain circuits. That means, then, that we can’t confidently state at this point that stone tool manufacture played a major role in the evolution of language. When exactly language made its appearance is therefore still a mystery to be solved.

We also discovered that Oldowan tool-making mainly activates brain areas involved in visual inspection and hand movement. More advanced Acheulian tool-making recruits a higher-order cognitive network that spans across a large portion of the cerebral cortex. This Acheulian cognitive network is involved in higher-level motor planning and holding in mind multi-sensory information using working memory.

Areas of the brain that form the Acheulian cognitive network that are also active when trained pianists play the piano. Shelby S. Putt, CC BY-ND

It turns out that this Acheulian cognitive network is the same one that comes online when a trained pianist plays the piano. This does not necessarily mean that early humans could play Chopin. But our result may mean that the brain networks we rely on today to complete complex tasks involving multiple forms of information, such as playing a musical instrument, were likely evolving around 1.8 million years ago so that our ancestors could make relatively complex tools to exploit energy-dense foods.

Shelby Putt, Postdoctoral Research Fellow, The Stone Age Institute and The Center for Research into the Anthropological Foundations of Technology, Indiana University

This article was originally published on The Conversation. Read the original article.

Shelby Putt received funding from The Leakey Foundation, the Wenner-Gren Foundation, Sigma Xi, the Scientific Research Society, and the American Association of University Women.

Science Speakeasy Showcases the Secrets of Science

How has evolution shaped gender, our favorite sports teams, and everyday life in general?
Those are a just few of the topics that The Leakey Foundation’s new Science Speakeasy event series will set off to explore. Science Speakeasy mixes science with storytelling, hands-on experiments, drinks and lively conversation.

Alia Gurtov, Leakey Foundation grantee and paleoanthropologist

The first event, “Out of this World: From Caves to Space”, will take place Tuesday, May 23rd from 6-9 pm at Public Works in San Francisco and will feature speakers discussing humanity’s past and future, as well as what it’s like to conduct research in the most extreme conditions.

Alia Gurtov, renowned “underground astronaut” archaeologist, will delve into the depths of our past as she discusses the Homo naledi fossils she discovered in the Rising Star Cave in South Africa. During her time in South Africa, Gurtov often worked in extreme conditions, more than 90 feet underground and in 98% humidity, squeezing herself and ancient, delicate fossils through the tightest of spaces.


Ariel Waldman is on a mission to make space exploration accessible to everyone.

Joining Gurtov will be Ariel Waldman, founder of and author of “What’s it Like in Space?”

Waldman sits on the council for NASA Innovative Advanced Concepts and is on a mission to make science and space exploration disruptively accessible to all. She founded her website with the aim of providing a directory of ways to participate in space exploration and hopes to enlighten others on clever ways that they can contribute to the furthering of science and space exploration.
The second Science Speakeasy event, “Evolution and Gender Revolution” will happen June 20th from 6-9 pm at Public Works and will coincide with San Francisco Gay Pride week as it explores the evolutionary origins of gender.
Evolutionary anthropologist Stephanie Meredith will kick off the event highlighting her work with primates, studying specifically how developmental systems produce behavioral sex differentiation.

SF Giants pitcher Madison Bumgarner on September 3, 2013. By SD Dirk on Flickr – CC BY 2.0

The third and final Science Speakeasy event, “A Giant Advantage: Baseball in Our Bones,” takes place July 12 from 6-9 pm at Public Works and examines how the ability to precisely throw a baseball is distinctive to human evolution.

Nathan Young, evolutionary biologist and UCSF professor, will be discussing how species develop and evolve their characteristic shape and size. He will look at limb proportions and relate human’s unique athletic abilities, specifically pitching and throwing, within the sport of baseball to the actual evolution of our bodies.
Also relating his perspective of baseball in our bones is Dr. Ken Akizuki, the orthopedic surgeon for the San Francisco Giants. Dr. Akizuki will talk about his background treating players injuries and how many cases he sees are the result of repetitive stress.
The Science Speakeasy event series was designed to inspire enthusiasm for science in a fun, spirited and accessible way, providing people with the ability to socialize and meet new friends.
“Science Speakeasy is a fun way for scientifically curious folks to learn new things in a non-traditional environment,” said Sharal Camisa, Executive Director of The Leakey Foundation. “We hope people with all sorts of interests will join us to learn about the truly fascinating qualities that make us human.”

March for Science

On April 22nd, The Leakey Foundation staff will be joining the March For Science in San Francisco, Santa Rosa, and New Orleans. Want to join us? You can meet up with our Leakey Foundation group in San Francisco , or download our sign and march with us virtually!

The March for Science website says the march “champions robustly funded and publicly communicated science as a pillar of human freedom and prosperity.” The Leakey Foundation has stood for these values for nearly 50 years.

We actively support scientific discovery and its dissemination to advance our understanding of life, from its origins to our survival. We’ll be at the March for Science on Saturday – we hope to see you there!

Download and print our signs and we will see you on the streets!

If you use our signs, please take a photo and tag us on social media. We will share your message on Twitter, Facebook and Instagram.

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From the Field: Jason Lewis

Last year we introduced you to Leakey Foundation grantee Jason Lewis who was awarded during our spring 2016 cycle. To read a short summary of his work, click here. Here he updates us on his team’s progress. 

Left to Right: Unknown, Ray Inskeep, Adi Inskeep, Louis Leakey

The Kondoa region in central Tanzania is a UNESCO World Heritage Center and home to dozens of rock shelters painted with dazzling and diverse ancient paintings. One of these shelters, Kisese II, is unusual for its deeply stratified artifact- and fossil-rich deposits, which span the Late Pleistocene to Holocene. Kisese II was excavated by Louis and Mary Leakey in 1951 and by Ray Inskeep in 1956, but the results were published only as preliminary notes. And the faunal and lithic materials have been moved to several museums over the past 60 years.  What we know from these preliminary notes, however, is that the Kisese II record is special; rich in ochre, it contains thousands of ostrich eggshell beads, lithic artifacts, diverse and well-preserved fossil fauna, and six human burials.

Together with Christian Tryon, Kathryn Ranhorn, Audax Mabulla, Amandus Kwekason and other collaborators, we’ve put together a new project to fully analyze the material from this important site and reveal their implications for understanding the interplay between changes in the environment, human population growth, and stone tool technology in this important period of Africa’s prehistory. We immediately relied upon archives to get started; thanks to Inskeep’s preliminary reports and curation efforts of the Tanzanian National Museum, we were able to obtain sixteen new radiocarbon dates across the sequence, showing that the >4 meter sequence spans the last fifty thousand years. In 2015 we visited the site to determine the current state of preservation of the rock art and the archaeological sequence and the feasibility of new excavations.

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Ray Inskeep’s personal archive

Thanks to funding from the Leakey Foundation, we’re now expanding on these results by focusing on the lithic artifacts and fossil fauna to understand changes in the environment, ecology, and foraging practices across multiple Late Pleistocene-Holocene human technological and behavioral shifts. Again, our first priority was to find more archival records, which led me to the McDonald Institute for Archaeological Research at Cambridge University in the UK in December 2016. This incredible facility enabled me to search Ray Inskeep’s personal archives for any contextual information that would help us when analyzing the Kisese II faunal and lithic material.  Hidden amongst a lifetime’s worth of records and remembrances, I was lucky enough to find correspondence between Inskeep and colleagues about the Kisese II project and photos of the site during work there, including one of Louis Leakey visiting the site. I also found Inskeep’s plans and sections from the excavation, and raw data on the lithic artifact counts by category and level.  This documentary evidence is of great importance for reconstructing a full context for the materials from the site.  While at Cambridge, I was also invited to give a lecture about this work in the Department of Archaeology and Anthropology’s Biological Anthropology Seminar Series.

Jason Lewis

With this valuable new archival information, I then traveled to Dar es Salaam to coordinate with Tanzanian project members and to collect enamel, dentin, bone, and OES samples from the Kisese II collection. I spent two weeks identifying appropriate specimens, photographing and recording them, and drilling off small amounts of bioapatite for export. These samples have been sent to Rhonda Quinn at Seton Hall University for isotopic analysis, the results of which will tell us more information about the past ecology- like what types of plants ancient animals ate around the site. A subset of mammal teeth was serially sampled up the crown to investigate changes in the degree of seasonality through time. We also exported more ostrich eggshell fragments, which Elizabeth Niespolo at UC Berkeley is analyzing to better understand the paleoenvironment. As part of our project’s outreach program, NMT staff members were trained in sample collection and preparation, a complete set of drilling equipment and supplies were donated to the museum, and we’re working together to develop an official policy on destructive sampling. A few days after I left Dar, project member Kathryn Ranhorn, a doctoral candidate at George Washington University, arrived and analyzed the lithic artifacts to discern changes in tool production behaviors.

Ray Inskeep

This work would not have been possible without the detailed record keeping of multiple parties, especially Ray Inskeep, the McDonald Institute, and the Tanzanian National Museum. Thanks to support from the Leakey Foundation, we look forward to continuing this important research started so long ago, to renewing excavations at the site, and to contributing new evidence to the archive of all humanity.

Letter from Louis Leakey to Ray Inskeep

Spring Granting Cycle Update

We are about two thirds of the way through our spring 2017 granting cycle, and I am sure many of you who have applied this time are wondering what is going on over there in the grants department at The Leakey Foundation. So, I thought I would tell you about the different stages of our spring cycle and give you an idea of where we are right now.

The spring granting cycle begins.

Immediately after the application deadline, the grants department begins the Audit Stage. This is the time when we make sure that all the pieces of the applications have been submitted and contact applicants if needed. We check to make sure all of the applications are within our purview (we do not fund projects about traveling to Mars), and we begin assigning peer reviewers and soliciting reviewer suggestions from our Scientific Executive Committee (SEC). The audit stage of our spring cycle typically lasts just over a month.

Once we have assigned peer reviewers, we begin the Peer Review Stage of the cycle.

Our goal is to receive at least two peer reviews from relevant experts in the field for each proposal. Because of this, we have to send out more requests than that to reach our goal. You are busy people! With huge workloads, prior commitments, field work, etc. many of our potential peer reviewers must decline our request. That said, we still receive numerous reviews each cycle. This spring we received over 250 reviews (for 102 applications) along with corresponding grades (we use an A,B,C… ranking system). The spring Peer Review Stage lasts about a month and a half.

We are always thankful for our peer reviewers. We could not do it without you!

Next is the SEC Review Stage, which is where we are currently.

We collate all of the peer reviews and send them to the SEC. Relevant members of our SEC then review the proposals, using the peer reviews as reference. This stage of the cycle typically lasts a few weeks.

We are a little different.

One of the main differences between the way we and other organizations that fund similar projects make granting decisions is that our Scientific Executive Committee makes the final decision. Other organizations typically use assembled panels of reviewers, but the final decision is made by the president or program director, sometimes in consultation with the panel.

For us, once the SEC Review Stage is complete, we combine all the grades into one large spreadsheet and then rank the proposals. We then have two conference calls (one for behavioral proposals and one for the paleoanthropology proposals) where the SEC decides which proposals they would like to fund. Decisions are not based solely on rank. They are also based on funding priorities of the foundation as well as discussions that ensue during these important calls.

One of our granting sessions

Once decisions are made, our SEC and Board of Trustees meet at our bi-annual Granting Session. The SEC presents each recommended proposal to our Board of enthusiastic science supporters. Once the proposals have been presented, our Board then votes to approve funding. In the spring this meeting occurs at the end of April.

Then we send out notifications.

We usually send out the spring notifications in the first week of May. One of the benefits of applying for a Leakey Foundation Research Grant is that the applicant receives feedback (the reviews) from peer reviewers and SEC members in an anonymous way. Even if we do not fund a project that cycle, it is our goal to help applicants improve or change their proposal in order to increase the chances of future funding from us or other organizations.

That is it! As I said, we are now in the SEC Review Stage. We will soon have those important conference calls and then the presentations to the board.

We wish you the best of luck in your endeavors. The grants department is here to help. If you have any questions about the cycle or the application process, feel free to contact us at


H. Gregory
Program Associate