New analysis on the human family tree
The story line of how modern humans got to be where we are is constantly changing as new evidence is found. This often forces us to confront the idea that we aren’t as unique as we thought, as we find evidence of behaviours like tool use further and further back in our family tree. New evidence hints that our ancestors may have left Africa—and gone farther from it—than we had thought previously.
A paper currently in press at the Journal of Human Evolution takes a look at how Homo floresiensis, the diminutive “hobbit” species, fits into this picture. Its findings suggest that the hobbit lies further down on the family tree than previously thought, something that would only be possible if our ancestors had migrated out of Africa much earlier than any other data suggested.
Our genus Homo may seem to have been pretty determined to get out of Africa. But Homo is a diverse group, a similar level of grouping to the one that places dogs, wolves, foxes, and jackals together in Canis. Across the genus, the migratory history is mixed. Our own species obviously left, probably in more than one wave of migration. But going much further back in time, our cousins Homo erectus, who lived between 2 million years and approximately 70,000 years ago, also left Africa and spread throughout Asia. Other members of our genus appear to have remained on their native continent.
It hasn’t been clear where the hobbit fit into this picture. Partly because it lived outside Africa (on the Indonesian island of Flores), the two primary hypotheses have paired it with the two species known to have had a presence in the region: H. erectus and us. Obviously, the tiny hobbit was much smaller than either of these species, but that can be explained by “insular dwarfism,” a phenomenon that frequently sees species becoming much smaller over evolutionary timescales when they live in an isolated island environment.
The question is whether the hobbit has features other than size that clearly group it with one species or another.
A group of researchers at the Australian National University, led by Debbie Argue, compared anatomical features of the hobbit to the same features from a wide number of other species. No matter which way they sliced it, the data told the same story: the hobbit kept showing up alongside not us, not Homo erectus, but Homo habilis, a much older species not known for its wanderings outside Africa.
What is right about this?
There is definitely some skepticism warranted here—not because the science is bad, but because there is just so much we don’t know about the past. The discovery of the hobbits themselves was “uncovering something that seems to have a history of a million years that no one had even guessed at,” says John Hawks, a paleoanthropologist at the University of Wisconsin-Madison.
The methods that Argue and her team used for their analysis involve some assumptions that deserve unpacking. This kind of computational analysis tries out lots of different evolutionary trees and picks those that best fit the data. So, two species with lots of anatomical similarities will end up close together on the tree, and species that are very different will be far away.
The hobbit ended up close to H. habilis because of anatomical features that were similar enough that this tree best explained the data. But the hobbit was clearly under enough evolutionary pressure to change radically in size, and that evolutionary pressure may have brought about other radical changes, too. “We do know from other dwarfed mammals that primitive features can seemingly re-evolve,” says Chris Stringer, a human evolution researcher at London’s Natural History Museum. “Some evolutionary reversals on the floresiensis lineage could well have occurred.”
So, the hobbit could have been grouped with H. habilis because, after undergoing a package of evolutionary changes, it ended up looking more like a distant ancestor than like its contemporaries in other parts of the world. The methods used to draw up hypothetical evolutionary trees assume that evolutionary changes will have been pretty minimal. “The trouble is,” says Hawks, “evolution may not be minimal.”
This discovery is likely to spawn a lot of debate. While it is another nail in the coffin of the hypothesis that the hobbits were modern humans with a genetic disorder, it brings a new challenge: the idea that either H. habilis itself, or a close relative, migrated out of Africa and underwent insular dwarfism on Flores. “It’s interesting work,” says Stringer. “[But] I don’t think it will settle the arguments.”
Hawks thinks it’s a bad idea to disregard this analysis just because we don’t currently have evidence of H. habilis outside Africa. “If you think that you have to fit the past to the few pieces of data you have now,” he says, “you need to look harder.”