A long-standing interpretation of small grooves found on the teeth of ancient human fossils is facing new scrutiny from the scientific community. For many years, these markings were widely considered to be the result of deliberate actions, such as cleaning teeth with sticks or other implements, a practice colloquially known as “toothpicking.” This behavior was often cited as one of the earliest forms of dental hygiene among our ancestors, with examples found in fossils dating back millions of years.
New research, however, is questioning this narrative by presenting evidence that suggests these grooves may not be unique to humans or indicative of tool use. A recent study published in the American Journal of Biological Anthropology has found similar grooves on the teeth of wild primates, where the use of tools for dental cleaning has not been observed. This discovery introduces the possibility that the grooves could be formed through natural processes, compelling paleoanthropologists to reconsider the origins of these dental features and what they reveal about the behavior of early hominins.
Revisiting Fossil Evidence
The “toothpick groove” hypothesis has been a part of the scientific discourse since the early 20th century, with numerous examples identified in the fossil record. These grooves, typically found on the exposed roots of teeth, especially between them, have been documented in a range of ancient human species, including Neanderthals and hominins as old as 2 million years. The consistent shape and location of these marks led to the conclusion that they were created by the repeated insertion of a tool, likely a small stick or piece of bone, to alleviate gum discomfort or remove food debris.
One of the most significant examples supporting this theory comes from a 1.2-million-year-old hominin molar discovered at the Sima del Elefante site in Spain. Researchers identified non-edible wood fibers within a groove on this tooth, which was interpreted as direct evidence of toothpicking. Similarly, a 130,000-year-old Neanderthal fossil from the Krapina site in Croatia exhibited multiple toothpick grooves, leading researchers to suggest it was a form of prehistoric dentistry to treat dental irritation. These findings have been widely accepted as proof of early dental hygiene practices.
A New Perspective from Primates
The latest research challenges the traditional interpretation by expanding the scope of investigation to include non-human primates. A comprehensive study of over 500 wild primates, spanning 27 different species, both living and extinct, revealed the presence of grooves that are virtually identical to those found in human fossils. Approximately 4% of the individuals in the study exhibited these lesions, which featured the same fine parallel scratches and tapering shapes as the “toothpick grooves.” This finding is significant because there is little evidence to suggest that these primates engage in tooth-picking behaviors.
The study proposes that these grooves may be caused by natural factors instead of deliberate tool use. The researchers suggest that the abrasion could result from the natural chewing process, especially with a diet that includes abrasive foods. Another possibility is the incidental ingestion of grit or sand with food, which could contribute to the formation of these marks over time. Certain specialized behaviors, such as stripping vegetation with the teeth, might also play a role in creating these grooves. This new evidence does not entirely rule out the possibility of toothpicking in ancient humans, but it indicates that not all such grooves can be automatically attributed to this behavior.
The Absence of Abfraction Lesions
In addition to the discovery of toothpick-like grooves in primates, the new study highlights the absence of another type of dental wear in the fossil record. The researchers found no instances of abfraction lesions, which are deep, V-shaped notches at the gumline, in any of the wild primates they examined. These lesions are common in modern humans and are often associated with factors like forceful tooth brushing, tooth grinding, and the consumption of acidic foods and drinks. The complete absence of these lesions in both ancient fossils and modern wild primates suggests that they are a uniquely modern human phenomenon.
This finding has important implications for understanding the evolution of human dental health. It suggests that the dental problems common today are likely a result of modern habits and diets, rather than natural chewing forces. The contrast between the presence of “toothpick grooves” and the absence of abfraction lesions in the fossil record provides a new lens through which to view the dental health of our ancestors and the impact of modern lifestyles on our own teeth.
Implications for Human Evolution
The questioning of the toothpick origin for dental grooves has broader implications for the study of human evolution. For decades, these marks were considered a clear indicator of a uniquely human behavior and cognitive ability: the use of tools for a specific, repeated purpose. If these grooves can be formed naturally, then their presence in the fossil record can no longer be taken as definitive evidence of such behavior. This necessitates a re-evaluation of the evidence for tool use in early hominins and a more cautious approach to interpreting dental modifications.
This new research underscores the importance of comparative studies in paleoanthropology. By looking at our closest living relatives, scientists can gain a better understanding of the range of natural variation and the processes that can affect skeletal and dental remains. While the idea of our ancestors practicing a form of dental hygiene is compelling, the scientific process requires that all possible explanations be considered. The debate over the origin of these ancient tooth grooves is a reminder that the story of human evolution is constantly being revised as new evidence comes to light.
