When researchers published findings in June of the earliest Homo sapiens fossils ever discovered, the scientific community was abuzz.
Three-hundred-thousand years old, 100,000 years older than anything previously discovered, they stretched the timeline of Homo sapiens, our distant ancestors, further into the past. It left humanity with a new first chapter, blank and waiting to be written.
But it was where the fossils were found that was more intriguing still. Ethiopia was previously the site of the oldest Homo sapiens fossils, and East Africa has long been considered the “cradle of life.” However, these new finds came from Jebel Irhoud in Morocco.
A long-held anthropological narrative became more complex. What were these hominids doing on the other side of the continent? Had they evolved in isolation to sapiens in East Africa? What happened during these extra 100,000 years, and could we determine a new starting point for humanity?
Excavated from what was once a barite mine 250 miles from the capital Rabat, the fossils were sent for study to the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. It was here in the thermoluminescence laboratory that advanced dating technology was used to determine the fossils’ age.
Alongside sapiens remains at Jebel Irhoud, archaeologists found stone tools that had been burnt with fire. Using thermoluminescence detectors, scientists could establish when an artifact was heated.
“If you have a strong light emission, you have an old artifact. If you only have a very low light emission, you have a very young artifact,” explains Tobias Lauer, a post-doctoral researcher at the institute.
“Normally you have an error range of about 10%. If you get an age of around 300,000 years, it means that you have plus (or) minus 30,000 … it’s extremely helpful for us.”
CT scans were also used to create hundreds of two-dimensional X-rays of the fossils, compiled to create three-dimensional avatars (see below, courtesy MPI). These computer models are an invaluable way to rebuild fossils that may have broken or missing pieces.
With the pieces assembled as best they could be, a team has been charged with filling in the blanks on the life of these ancient sapiens.
“It’s like a puzzle,” says Jean-Jacques Hublin, director of the department of human evolution. “We have to put together, to reconstruct, not just the anatomy of these humans but also their lifestyle, their activities.
“The face of these people is a face like my face; it’s a face (like) somebody you could cross in the street today,” he adds. But there are still significant differences.
“(Through) the course of 300,000 years many things happen, and in particular their brain case and the brain inside is big, but is different in morphology to what we have today – we suspect not just in morphology but also in the kind of wiring of the brain.”
The bridge between the Moroccan fossils and us is “mostly a story of brain evolution,” says Hublin.
“Recent discoveries in paleogenetics and genetics show that in this time period, there were a series of mutations affecting brain functioning, brain connectivity, brain development that occurred within our lineage.
“It seems to be something specific to our species that we don’t find in other groups of the same period, like Neanderthals or Denisovans or others.”
But while there’s a strong record of the evolution of many other hominids, “the origin of our own species is much more mysterious,” says Hublin.
Until recently it was considered a sort of “enigmatic emergence” of Homo sapiens occurred, originating from sub-Saharan Africa, most likely East Africa, from a “restricted area” and occurring quickly. The find at Jebel Irhoud has caused this narrative to be “completely revised,” says the study leader. This doesn’t mean Morocco is the new cradle of life; instead, that our ancestors were much more dispersed, and much earlier, than previously thought. (It’s worth noting that at the time the Sahara was not a desert, but in fact a lush green grassland, rich in flora and fauna.)
“The notion that somehow just a corner of Africa is involved in the origin of our species – I think we can forget it,” says Hublin. “If there is a Garden of Eden in Africa, this Garden of Eden is the size of the continent.”
As announced earlier this year, the institute, a pioneer in the field of fossil DNA extraction and genome mapping, was unable to recover DNA samples from the current Jebel Irhoud find. But this month archaeologists returned to the excavation site to source more artifacts for testing.
They’re working with a firmer platform and greater understanding of our origins than before.
“Science is a sort of perpetual reworking of knowledge,” muses the project leader. “The tree of hominids is a tree with a picture that is a bit fuzzy. There are many parts that are visible, and so what we’re doing is we’re completing this picture … or having a picture that is more in focus.
“I think with Jebel Irhoud, we touched an essential branch of this tree. Because it’s our branch.”