Human evolution is a complex business, especially during the Middle Pleistocene, when much of the planet was in the grip of the last ice age and a group of big-brained primates in Africa was busy diverging into multiple species, one of which would eventually turn into us.
Now, an international team of researchers is proposing a way to make sense of an increasingly confusing fossil record from the period, which stretches from about 780,000 to 126,000 years ago. The proposal includes retiring two species names that the researchers say no longer make sense and adding a new species that was the immediate precursor to our own, Homo sapiens – but not our close cousins the Neanderthals.
“We started off by wanting to be able to talk intelligently about diversity, movement and interactions among these different groups … In the end that was impossible without naming a new species,” said Mirjana Roksandic, a professor of bioanthropology at the University of Winnipeg and the lead author of a paper that makes the case for reorganizing the human family tree during the Middle Pleistocene.
In its paper, published Thursday in the journal Evolutionary Anthropology, the team proposes calling the new species Homo bodoensis. The name comes from Bodo, an excavation site along the Awash River in Ethiopia, where a fossilized cranium of a large-brained member of the Homo genus was discovered in 1976. That specimen was previously classified as belonging to the species Homo heidelbergensis, whose type specimen was discovered in Germany in 1907. In some versions of how humans originated, Homo heidelbergensis is considered the ancestor of all later human groups, including Neanderthals and Homo sapiens.
Based on its skull size, the Bodo specimen was a human ancestor, but the team notes that it lacks any features found in Neanderthals. It may be related to other members of the Homo genus that seem to stand apart from Neanderthals and spread into the Middle East and the Balkans during the Middle Pleistocene, including one that is known only by part of a jawbone, discovered in Serbia by Dr. Roksandic more than a decade ago.
She said the evidence doesn’t support the idea that Homo heidelbergensis was found in Africa or that it gave rise to modern humans. Instead, the team argues that the Homo heidelbergensis fossils found in Europe are just early Neanderthals and so do not need a separate species name.
“It has always been considered to be something of a garbage can [designation] in that anything that could not be assigned comfortably to another group would be simply dropped into Homo heidelbergensis,” said Christopher Bae, an anthropologist at the University of Hawaii at Manoa and a co-author of the paper.
In the alternative interpretation proposed by the team, it was Homo bodoensis that arose in Africa, where it diverged from our last common ancestor with Neanderthals about 800,000 years ago and later gave rise to Homo sapiens. Such an arrangement of the human family tree would also eliminate the need for another species name, Homo rhodesiensis, which is based on a fossil found in 1921 in what is now Zambia, formerly called Northern Rhodesia, after British colonialist and mining magnate Cecil Rhodes.
In its paper, the team write that, in addition to being extraneous, the name Homo rhodesiensis “is associated with sociopolitical baggage that our scientific community is trying to dissociate itself from.”
Yet the team’s proposed changes could start as many debates as they settle. Anthropologists are sometimes categorized as “lumpers” or “splitters,” based on whether they tend to lump fossils that are similar into a common species or focus on differences that may indicate a split into separate species. By naming a new species and eliminating two others, Dr. Roksandic said wryly that she and her colleagues may have found a way to irk both sides at the same time.
Bence Viola, a professor of anthropology at the University of Toronto but not a member of Dr. Roksandic’s team, said the paper is correct in pointing out the ambiguities around Homo heidelbergensis and he agreed that the name Homo rhodesiensis “is fraught.”
“What I am not sure about, though, is whether naming a new species is really the solution,” he said.
He added that because DNA evidence makes clear that our direct ancestors interbred with Neanderthals and other groups, naming a new species simply adds another label without biological meaning.
“One possibility would be to just refer to the [African] specimens as Homo sapiens, similar to the approach taken to the European fossils that get lumped into Neanderthals,” he said.
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