Ancient pitted teeth reveal new evolutionary marker in human ancestors

Teeth are archives. Every pit, ridge, and wear pattern holds information about how an organism lived and where it belongs in the family tree of life. For paleoanthropologists, the enamel surface of a fossil tooth can reveal whether an ancestor suffered malnutrition as a child, how it chewed its food, and sometimes even which species it belonged to. But a new study published in the Journal of Human Evolution suggests that what scientists have long dismissed as damage—tiny, shallow pits scattered across the enamel of ancient hominin teeth—may actually be something far more useful: a genetic marker that helps trace the evolutionary relationships between our ancestors.

The pits in question are remarkably consistent. They are uniform in shape, circular, and shallow, appearing in regular clusters on specific regions of the tooth crown. Researchers first noticed this pitting pattern in Paranthropus robustus, a close relative of our own genus Homo that lived in South Africa. Initially, scientists assumed these were defects—signs that the individual had suffered illness or malnutrition during childhood, when tooth enamel forms. But when researchers examined fossil teeth from sites across Africa, including the Omo Valley in Ethiopia and southern African locations like Drimolen, Swartkrans, and Kromdraai, they found the same pitting pattern appearing consistently across multiple species and millions of years. The pitting showed up not only in Paranthropus robustus but also in other Paranthropus species from eastern Africa and in some early Australopithecus individuals—a genus that may have been ancestral to both Homo and Paranthropus. This geographic and temporal consistency suggested something more interesting than random disease or malnutrition was at work.

The evidence against the defect hypothesis is compelling. Stress-related tooth damage typically forms horizontal bands across the enamel and affects all teeth that were developing at the time of the stress. The pitting observed in these ancient hominins follows neither pattern. It does not correlate with tooth size or enamel thickness, and it does not preferentially affect front teeth over back teeth or vice versa. Instead, the pits appear in a regular, almost deliberate arrangement—the kind of pattern you would expect from a genetic trait rather than an environmental insult. The researchers propose that this pitting likely emerged as a byproduct of changes in how enamel formed in these species, possibly even serving some unknown functional purpose. Whatever its origin, they argue it should be understood as a trait, not a defect.

A modern parallel strengthens this interpretation. Today, about one in 1,000 people carry a rare genetic condition called amelogenesis imperfecta, which disrupts enamel formation and produces pitting similar to what researchers see in the fossils. But here is the crucial difference: the uniform pitting found in ancient hominins appears in up to half of some Paranthropus populations. A condition that severe and that common cannot reasonably be classified as a harmful disorder. Moreover, the pitting persisted at similar frequencies for millions of years, suggesting it was neither selected against nor particularly disadvantageous. This pattern is consistent with a heritable trait that became established in certain lineages and remained stable across deep time.

If the pitting is indeed genetic, it becomes a tool. Paleoanthropologists already use subtle dental features—enamel thickness, cusp shape, wear patterns—to identify species and trace relationships. The uniform pitting may now join this toolkit. The findings support the idea that all Paranthropus species descended from a relatively recent common ancestor rather than evolving independently from different Australopithecus populations. Notably, the pitting does not appear in the southern African species Australopithecus africanus, despite examination of more than 500 teeth from that species. But it does appear in the earliest Australopithecus specimens from the Omo Valley. This geographic and temporal distribution could help pinpoint where Paranthropus branched off on its own evolutionary path.

One case stands out as particularly intriguing: Homo floresiensis, the so-called hobbit species from Indonesia. Based on published images of their teeth, these small hominins appear to show similar pitting. If that observation holds up under closer examination, it could suggest that H. floresiensis had an evolutionary history more closely tied to early Australopithecus than to later Homo species. But caution is warranted. H. floresiensis also shows signs of skeletal and dental pathologies, so more research is needed before drawing firm conclusions. The same applies to the pitting itself. Scientists need to understand the developmental processes behind it more fully before it can be used routinely to classify and relate fossil species. Still, the research demonstrates that this pitting is likely heritable, that it appears nowhere in living primates, and that it is absent from our own genus Homo—except in rare cases of amelogenesis imperfecta. As such, it offers a new window into how our ancient relatives were related to one another, and how the branches of the hominin family tree diverged over millions of years.