Near the end of the last glaciation, a group of people walked barefoot along the shores of Lake Natron. They walked side by side, their paths never crossing each other as they headed southwest. It’s tempting to wonder what they might have thought if they’d known that the soft volcanic ash beneath their feet would preserve their tracks for thousands of years.

Bones can tell you things about how a person lived their life, but footprints are a snapshot of action in progress. It’s one thing to know that an ancient person spent a lot of time throwing things or carrying things, and it’s something much more immediate and personal to see exactly where that person walked, climbed a slope, or crawled into a muddy cave. Footprints, in some ways, are more startlingly intimate links to the past than bones. And at Engare Sero, just south of Tanzania’s Lake Natron, 408 footprints reveal how an ancient group of hunter-gatherers foraged.

The other half of the hunter-gatherer economy

Today, the footprints offer a look at something that’s often missing from the archaeological record: the work done by women and the gathering half of the hunter-gatherer economy. Based on the size, depth, and proportions of the prints, it looks likely that 14 of the people walking by the ancient lakeshore were women. Two of the others were probably adult men, and the last was probably a young man.

Overall, the situation looks very similar to how women in modern hunter-gatherer groups, like the Ache and the Hadza, go about the work of foraging. Children stay behind in camp, unless they’re young enough to need nursing, in which case the mother has to carry a baby all day while hiking and foraging. The women set out in a group, and men sometimes walk along to visit or accompany them.

In most places where people still make their living by hunting and gathering, it also turns out that they have a tendency to walk along lakeshores when they’re foraging, while local wildlife tends to walk to and from the lake to drink. That’s how the tracks are laid out at Engare Sero; 24 zebra and buffalo tracks pass southwest of the group of foragers, crossing the humans’ path on the way to the lake.

“This scenario seems a plausible fit,” wrote archaeologist Kevin Hatala of Chatham University and his colleagues, referring to a lakeside stroll. “Other possibilities could certainly exist, however.” Archaeologists often look at how people live today to try to make sense of how other people lived in the past. In this case, the comparison seems to line up pretty well, but it’s important to remember that modern hunter-gatherer groups aren’t unchanging relics of the past.

Back and forth

What’s harder to figure out is why six more people were in such a hurry to head back northeast, in the opposite direction from the main group. One woman was running, based on the length of her strides, while another woman and a man seem to have been walking quickly. Another man and two women walked northeast at a more leisurely pace.

Hatala and his colleagues say these six people probably weren’t moving together, since they were all going at different speeds. It’s easy to imagine people heading back to camp at various points to fetch things or relay messages like “Hey, there’s a herd of zebra over there.” But we have no way to know exactly what they were up to.

Of course, guessing someone’s sex based on their foot size isn’t a sure thing. Hatala and his colleagues calculated the most probable age and sex for each person in the party, but “probably female” can mean a 50 to 60 percent probability of being female rather than male. Hatala and his colleagues say it’s especially difficult to be sure if a track belonged to an adolescent boy or a small-statured woman. But a mostly female group makes sense, given how other hunter-gatherers live in a similar landscape.

Walking in an ancient landscape

It’s hard to say exactly how long ago this ancient foraging party left the Engare Sero tracks. In an earlier study, argon isotope dating of the sediment suggested that they’re around 5,700 years old. Hatala and his colleagues dated calcite in another layer of sediment, above the footprints, to between 12,000 and 10,000 years old, so if they’re right, the tracks can’t be any younger than that—and they could be as old as 19,000 years.

That’s probably a question that’s going to take more dating, and more data, to resolve. And there are more tracks waiting at Engare Sero. “Along the northern boundary of the excavation, several trackways lead directly beneath unexcavated sediments,” wrote Hatala and his colleagues. But they won’t be unearthed “until a long-term site conservation plan is implemented, as we know the exposed portion of the site is subject to erosion.”

In fact, erosion revealed the first 56 tracks to members of a local Masai community, who discovered them in 2009. Over the next few years, archaeologists carefully excavated 352 more human footprints, plus tracks from ancient wildlife. The tracks are about 100km away from Laetoli, where another line of tracks marks the footsteps of one of our earliest hominin relatives, Australopithecus afarensis. That comparison underscores how deep and ancient our species’ roots are in Africa but also how much change has played out on that landscape over 3.6 million years.

Scientific Reports, 2020 DOI: 10.1038/s41598-020-64095-0  (About DOIs).

https://arstechnica.com/?p=1676759