High on a sheer cliff in South Africa's Swartberg mountain range last September, University of Utah paleoclimatologist Tyler Faith finally reached something he hoped might solve one of anthropology's stickiest mysteries. His target looked like goo that had oozed from the sandstone cliff and hardened into a foot-thick slab of black amber. Gas mask on, Faith got to work hewing away a 70-pound chunk; dust flung from his chainsaw quickly filled the air with a yellow-gold haze.

“It just gets in your pores,” Faith says. “The second you jump in the shower and that stuff finally rehydrates, it's like: Imagine the most stinky alleyway where people have been peeing. It's awesome. But yeah. All my gear now smells like pee.”

The substance is fossilized urine from untold generations of marmotlike critters called rock hyraxes—and it acts as an excellent record of the ancient climate. Sticky and viscous like molasses, hyrax urine hardens quickly in air. It traps pollen grains and charcoal, telling scientists when particular plants grew and wildfires raged. It also preserves chemical isotopes indicating precipitation and temperature. And the neat layers of the urine mounds or “middens,” which form where the animals habitually relieve themselves, can be precisely radiocarbon-dated.

Faith and his colleagues are using these clues to investigate controversial links between ancient climate change and a dramatic technological leap that occurred between 66,000 and 25,000 years ago, from the Middle to the Later Stone Age: that's when our early ancestors developed new tools and cultural strategies that modern hunter-gatherers still use today. The researchers are using hyrax middens to build a high-resolution regional climate history for South Africa, where a team of students and scientists from across the continent is also re-excavating Boomplaas Cave—one of very few places with a rich archaeological record of humans' transition into the Later Stone Age.

“It's really a period where the lights get turned on in terms of complex social and technological behavior,” says the team's excavation leader Justin Pargeter, an archaeologist at New York University and the University of Johannesburg. “The behavioral innovations across this transition were highly successful. And they led to our species really starting to dominate the ecosystems that they lived in.”

Later Stone Age people seem to have started making a priority of “economizing something,” says University of Michigan anthropologist Brian Stewart, who is not involved in the research. Whether limited by raw materials, time or perhaps their tool kit's weight, people of this time began crafting smaller, more modular stone tools whose “bladelets” could be swapped out like today's replaceable drill bits. Symbolism and social organization advanced, too: Pargeter notes that Later Stone Age sites are full of beads, which could be used to signal belonging and identity, as well as ocher, a clay pigment used to paint bodies and add identifying symbols to objects.

The Later Stone Age began in the run-up to the peak of the last Ice Age, and many researchers think the period's climate could have contributed to humans' technological and behavioral changes. Some propose that an increasingly volatile climate may have forced our ancestors to get more creative at effectively exploiting resources. But this is tricky to rigorously prove, particularly because in much of Africa the transition began just beyond the limit of radiocarbon dating—which doesn't work well for samples more than 50,000 years old. Without accurately dated archaeological material, it's impossible to draw clear lines between climate events and technology.

A biologist cuts through a hyrax midden with a saw in a golden-hued image.
Brian Chase sampling a hyrax midden in the Kordiersrivier Valley in South Africa. Credit: Tyler Faith

Boomplaas Cave offers a way around this problem. The transition out of the Middle Stone Age began later there, so the cave's artifacts are within reach of accurate radiocarbon dating. And Boomplaas is one of few archaeological sites on Earth with a continuous record that spans the transition. But researchers here face another challenge: South Africa's sparse climate history.

“We don't have traditional archives like ice cores or [cave deposits] and lake records,” says the research team's pollen expert, paleoecologist Lynne Quick of Nelson Mandela University. “So before the hyrax midden stuff, we had very limited and discontinuous records.”

Most attempts to link climate change to the Later Stone Age transition have focused on measurements from polar ice cores and deep-sea sediments. But these materials primarily reveal general, global climate trends. As with anthropogenic climate change today, ancient climate change affected different areas in different ways. Faith says South Africa's paleoclimate is still so little known that it's unclear whether the region was dry and harsh or wet and lush at the peak of the last Ice Age.

Team member Brian Chase, a paleoclimatologist at the University of Montpellier in France, saw a possible solution to this puzzle in hyrax middens, where these small mammals—which look like rodents but are more closely related to elephants—have dutifully returned to do their business for millennia. Chase has devoted his career to unlocking these overlooked data troves and has collected hundreds of samples from southern Africa. “Personally, I think they're the best paleoenvironmental archives on the planet,” Chase says. “It is a uniquely rich resource.”

These middens are “beautiful” archives, Stewart says, because they can be radiocarbon-dated along with the nearby Later Stone Age transition artifacts. “These are continuous records, and that's an amazing thing to have—just like the ice cores, but they're right next to your site.”

“This is the way we're going to actually move forward,” he adds, “instead of making these kind of wavy pronouncements about what the climate is doing at a global level.”

Faith, Chase and Quick sampled middens near Boomplaas Cave last September and received the first radiocarbon dates from the samples earlier this year. Combining the continuing Boomplaas excavations with their unconventional climate record, the researchers say, offers a real shot at finally unraveling the contentious links between climate and technological change in the Later Stone Age—and beyond.

“There's this whole other sphere of questions that we're going to be able to jump into by having those giant blocks of pee to play around with,” Faith says. “We hope it'll be useful to a lot of people.”

Editor’s Note (3/21/23): This article was edited after posting to correct the spelling of Justin Pargeter’s name.