A tiny pre-human who lived more than 900,000 years ago in what is now Kenya may have been a “short experiment” in evolution that never quite made it, scientists said Thursday.
The little skull clearly belongs to an adult and was found last summer at a site where much larger hominids classified as Homo erectus lived, Richard Potts of the Smithsonian Institution and his research colleagues reported.
He or she died on a volcanic ridge, perhaps mauled by a lion or other carnivore, Potts said.
It is the smallest adult fossil found dating back to the time of Homo erectus, the species of pre-human that dominated between 500,000 and 1.7 million years ago, Potts’ team writes in Friday’s issue of the journal Science.
Periodic gene-swapping
Potts believes the fossil find shows that early humans lived in little groups that became separate and distinct for a while, and then came together every few thousand years or so, swapped genes and then parted ways again.
“On occasion, they became isolated for a while, possibly hundreds of generations, and so developed their own unique combination of features,” Potts said in an e-mail.
But dramatic climate and environmental changes known to have occurred during those times forced groups to move together again, and perhaps drove some into extinction.
Perhaps there were lots of “short experiments” — species that never really quite made it, Potts said.
“In this light, I would see the hominid population at Olorgesailie as part of a single, highly variable species, with both large and small (possibly male/female) adults.”
Violent death
This particular early human was found in an area that would have been a volcanic ridge 900,000 years ago. Potts’ team is working, as anthropologists often do, from fragments of skull -- and guessing what the rest of the creature looked like.
It had carnivore bite marks on the left brow ridge, Potts said. “Quite possibly this is how the individual died. It was walking along or near the volcanic ridge leading up to the highlands (a safer nighttime place to be than by the water’s edge in the lowland) and it didn’t quite make it.”
Remains of large tools have been found in the area, where Potts and colleagues have worked for years.
“The entire area was a grassy plain, filled with grazing zebra and very large grass-eating baboons, along with grazing elephants and huge pigs,” Potts said. “The toolmakers made extensive use of the volcanic rocks up on Mount Olorgesailie and surrounding highlands — we’ve identified 14 different types of volcanic rocks that they chipped into handaxes.”
Species or subspecies?
Homo erectus remains have been found in parts of Africa, southern Europe and Asia. These hominids made tools and lived in groups, but anthropologists are trying to figure out whether there were separate species or subspecies among the group.
This particular individual will be difficult to classify, Potts said.
“It’s really too hard to say what species it is, if you happen to think there were multiple species around at the time. I certainly used to think so,” he said.
He has compared the skulls of fossils found from other hominids that lived around the same time, including Homo antecessor from Atapuerca in Spain or Homo cepranensis, from Ceprano, Italy.
“I find the variability in the skulls (and parts of skulls) impossible to divide neatly into separate lineages that stay consistently identifiable over any length of time, like Homo erectus in Asia does,” Potts said.
