Imagine five people out walking together along a river. Three are adults, the other two of juvenile age. As they walk together, they leave footprints in the mudflats.
Eight-hundred-thousand years later, a team of 12 archaeologists led by Nick Ashton of the British Museum and University College London announced its discovery of those footprints.
Media across the globe, including NPR, reported the news.
These footprints are the oldest known outside of Africa — a monumental discovery for archaeology and anthropology, made possible because severe coastal erosion in that region of England is, in the archaeologists' words, "both revealing and rapidly destroying sites that are of international significance."
The scientists can't know for sure which human ancestors made the footprints, because no skeletal remains have been found in association with them. Even though the footprints are referred to as "human," we know their makers weren't us — Homo sapiens, or anatomically modern humans. Our species evolved only around 200,000 years ago in Africa and arrived in the what is now the United Kingdom at around 40,000 years ago. A species called Homo antecessor is a leading candidate for the footprint makers.
For me, the most intriguing aspect of this find is what we can learn — and what we can't — from the fact that five individuals walked along together in a cluster.
In the BBC coverage of the discovery, one of the archaeologists, Isabelle De Groote, refers to the group of five walkers as a family:
[The footprints] appear to have been made by one adult male who was about 5ft 9in (175cm) tall and the shortest was about 3ft. The other larger footprints could come from young adult males or have been left by females. The glimpse of the past that we are seeing is that we have a family group moving together across the landscape.
At this, my skeptical radar kicked in. We're often too ready to assign a particular type of social organization to evidence from the past, going further than the evidence really allows. My favorite example of this tendency can be seen at New York's American Museum of Natural History. There, a famous diorama is meant to depict who made the earliest-known footprints in Africa (which means also the earliest known footprints anywhere in the world, since human ancestors then only lived in Africa). These footprints, from Tanzania, are dated to 3.6 million years ago. In the diorama, a male australopithecine is striding along with his arm draped over a smaller female's, as if protectively.
Voila! The pair bond, projected all the way back into our early prehistory!
In fact, there's no evidence of pair bonds that far back. The Tanzania footprints only tell us that one larger and one smaller individual walked along together.
As a woman nearly 6-feet tall, who often walks along with a friend only a little over 5-feet tall, I sometimes think future archaeologists would classify my footprints as male (unless, perhaps, my pelvis were found intact right alongside my footprints) and hers female. An exercise I routinely give my anthropology students is to think up alternative, equally valid, dioramas to represent the Tanzania footprints, starring not only a taller and shorter female, but also a taller and shorter male or an adult and an older juvenile.
I emailed Nick Ashton to ask him his own view about this matter, and he replied with a mix of scientific caution and openness to the idea of a family group:
The size ranges certainly suggest both adults and children with the largest being more likely a male, from what we know of the skeletal evidence from a site of the same age at Atapuerca in northern Spain. Therefore a likely interpretation is that we have a family group. I wouldn't put it more strongly than that however.
In other words, a family group is absolutely possible, but we shouldn't forget other alternatives exist. Perhaps the larger group had sent out a mixed-age foraging party to collect food resources, or perhaps the five people were just friends sharing a walk.
I also asked Ashton for his sense of what these newfound footprints mean to science, and whether he himself had any emotional reaction to the discovery. He wrote back:
I think the primary significance is the rarity of finding a snapshot in time or a day in the life of a probable family group walking along the edge of an estuary over 800,000 years ago, as it gives a very tangible link to the past that you don't get from stone tools or bones.
For me, when I was fully convinced that these really were human footprints and that we'd eliminated all the other possibilities, [my reaction] was one of astonishment and excitement. The eureka moment was when I received an email attachment with the processed overhead images, when the full features of the feet, including toes in one case, could clearly be seen.
As science writer Kate Wong put it when she blogged about the footprints for Scientific American:
There's just something about ancient footprints that makes the heart beat faster.
The joy of anthropology and archaeology comes in catching glimpses like this of our own prehistory: of the people who came before us, and whose struggles and successes paved the way for us to be here today.
You can keep up with what Barbara is thinking on Twitter: @bjkingape