An international team of biological anthropologists has found a novel way to reconstruct tens of thousands of years of human population history in north-eastern Africa: by examining tiny variations in the shape of the bony cavities that once contained people’s inner ears. It's not good news for creationists so it'll be just one more thing for them to ignore one way or another.
The researchers, led by Nicolas Martin and Isabelle Crevecoeur of the PACEA laboratory at the University of Bordeaux and the French National Centre for Scientific Research (CNRS), have published their findings in Nature Communications.
The bony labyrinth is a complex system of cavities within the temporal bone of the skull. It surrounds the cochlea, involved in hearing, and the semicircular canals, involved in balance. Although its shape varies subtly between individuals and populations, much of that variation reflects inherited ancestry. High-resolution micro-CT scanning allows the labyrinth to be reconstructed and measured in three dimensions without damaging the remains.
This makes it especially valuable in regions such as north-eastern Africa, where heat and other environmental conditions have frequently destroyed ancient DNA. When molecular evidence is unavailable, the shape of the inner ear can preserve an anatomical record of biological relationships between ancient populations.
Martin and his colleagues analysed 194 bony labyrinths belonging to 148 individuals. Their sample included people who lived between approximately 44,000 and 3,000 years ago in the Middle Nile Valley, the Horn of Africa and Central Africa, together with comparative specimens from elsewhere in Africa, Europe and the Levant. The researchers applied three different methods of shape analysis, all of which produced the same broad patterns.
Those patterns reveal a long and complicated history of regional continuity, isolation, migration, interaction and partial population replacement. Late Pleistocene and Early Holocene hunter-fisher-foragers from the Middle Nile Valley showed broad morphological similarities both to one another and to still earlier African Homo sapiens. This is consistent with deep regional ancestry and substantial biological continuity extending across many thousands of years.
That continuity was disrupted during the Neolithic transition. Beginning about 8,000 years ago, food-producing populations with distinctly different inner-ear morphologies appeared in the Middle Nile Valley, supporting the conclusion that pastoralism and agriculture arrived with migrating people rather than being adopted solely by the region’s existing foragers.
This was not necessarily a simple or complete replacement. Individuals retaining affinities with the earlier foragers survived for several millennia in areas bordering the Nile Valley, while some remains display combinations of characteristics consistent with limited interaction or admixture between the old and new populations. Samples from the Horn of Africa and Central Africa also showed considerable morphological diversity, indicating population substructure and differing regional demographic histories.
These results independently support earlier research by Martin and many of the same colleagues, which detected a similar Neolithic population discontinuity from the internal structure of ancient teeth. A CNRS account of that earlier study explains how enamel–dentine junctions revealed population replacement and continuing interaction along the Nile and its Saharan margins. Now two independent anatomical systems—teeth and inner ears—have produced compatible reconstructions of the region’s population history.
This presents creationists with the familiar problem of evidence that should not exist if their mythology were true. According to the young-Earth version of the biblical story, the entire human population was reduced to Noah’s family only a little over 4,000 years ago. Every population on Earth must therefore have descended from that tiny group after an extraordinarily rapid dispersal from somewhere in the Middle East.
But that is not the history recorded in these African remains. Instead, they document populations with roots extending tens of thousands of years into the past, sometimes remaining regionally continuous, sometimes becoming partially isolated, and sometimes meeting, mixing with or being displaced by migrants. There is no sign of a recent global population bottleneck, no interruption caused by a worldwide flood and no sudden appearance of all modern human diversity from a single family.
Nor does the conclusion depend exclusively upon ancient DNA, which creationists can dismiss without understanding it. The same evolutionary history is recorded in the physical anatomy of the people themselves and is independently supported by their teeth, their inner ears, archaeological evidence and the changing climate of the Sahara and Nile Valley. Once again, the evidence tells the coherent story of real populations changing through deep time—not the biologically impossible story of humanity restarting after a recent act of divine genocide.
The researchers do not claim that the shape of an inner ear can reveal every detail of an individual’s ancestry, nor that their sample represents every population that lived across north-eastern Africa. They acknowledge that some regions, particularly the Lower Nile Valley, remain poorly represented and that the anatomical evidence alone cannot distinguish conclusively between such processes as isolation, endogamy, genetic drift and founder effects. That scientific caution does not weaken the patterns they found; it defines precisely what the evidence can and cannot establish.
What it does establish is a population history extending across tens of thousands of years. Three different methods of analysing the bony labyrinth produced compatible results, while the demographic discontinuity associated with the arrival of food producers independently matches the pattern previously recovered from dental anatomy. Different parts of the human skeleton are therefore telling substantially the same evolutionary story.
That story contains regional continuity, periods of isolation, migrations, population structure, limited admixture and partial replacement. What it does not contain is a reduction of humanity to a single Middle Eastern family approximately 4,300 years ago, followed by the implausibly rapid creation of all subsequent human diversity. Neither is there any trace of a global catastrophe interrupting the archaeological and biological record at the time creationists insist their Flood occurred.
This evidence cannot be dismissed as a peculiarity of ancient-DNA analysis because no ancient DNA was needed to obtain it. The history is preserved in inherited anatomical variation, corroborated by teeth, archaeology and palaeoenvironmental evidence. Creationists must therefore dismiss several mutually supporting lines of evidence simultaneously, while offering nothing beyond an ancient myth to replace them.
Meanwhile, the scientists have again used evolutionary theory exactly as a successful scientific theory should be used: to formulate questions, interpret variation and reconstruct events that occurred long before written history. Far from abandoning evolution because the evidence contradicts it, researchers continue to extend its explanatory reach—even into the tiny bony labyrinths hidden inside the skulls of people who lived tens of thousands of years before creationists believe the world existed.
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