Did gum disease make us human?
- Ñî¹óåú´«Ã½ University
New study flips the script on evolution.
Human evolution is generally explained through changes in brain size, locomotion, or tool use, but new research from Ñî¹óåú´«Ã½ University suggests that gum disease and changes in facial structure may have been important factors in shaping the evolutionary path that ultimately led to modern humanity.
"Periodontal diseases are among the oldest recognised diseases in human evolution," says Professor Ugo Ripamonti from the Department of Internal Medicine, School of Clinical Medicine and lead author of the study .
"The fossil record allows us to investigate not only when these diseases emerged, but also how they may have influenced the evolutionary trajectory of our species."
Researchers Ripamonti, Dr Laura Roden (Coventry University, UK) and Jakobus Hoffman (South African Nuclear Energy Corporation) examined 71 fossil jaws dating back between 5.3 and 2.6 million years from collections housed at Ñî¹óåú´«Ã½ and the Ditsong Museum of Natural History.
The team found that species in the genus Homo experienced significantly greater alveolar bone loss due to periodontal disease than their Australopithecine relatives.
Alveolar bone supports and anchors the teeth in the jaws, and its loss and deterioration is a sign of periodontal disease.
"We found that the homo species developed significant alveolar bone loss, with distinctive crater-like lesions and defects around the teeth that were largely absent in Australopithecines," says Ripamonti.
The findings point to a possible link between alveolar bone loss in the Homo genus and the evolutionary changes that gave rise to modern humans.
"We typically view disease as purely destructive," says Ripamonti. "But in this case, periodontal disease may have interacted with other biological changes in ways that contributed to the emergence of human form."
However, to understand the leap from diseased gums to human intelligence, we must consider the skulls of our pre-human ancestors. Simply put, these were dense with large, powerful jaws, thick facial muscles, and large teeth to crush and masticate though food like edible roots.
While this anatomy allowed them to chew through tough vegetation, it also created a tight structure around the brain's cavity, effectively locking it in place and limiting its growth.
The researchers propose that chronic gum disease with important alveolar bone loss created a domino effect that shattered this anatomical cage.
There was a mutation that resulted in smaller tooth crowns. These smaller crowns could still cope with chewing, but they also contributed to a reduction in the facial muscles used for mastication. As chewing demands became lower, the large facial muscles began to shrink. These genetic changes led to progressively smaller tooth crowns, which generated weaker chewing forces while still allowing effective chewing and survival. Reduced chewing ability may, in turn, have contributed to a reduction in prognathism — the forward projection of the jaw and face seen in many earlier hominins.
Over millions of years, a less protruding face may have created space for expansion of the cranial vault, paving the way for the rapid brain growth that defines modern humanity.
Importantly, the study challenges the traditional “survival of the fittest” narrative by showing how a common illness can interact with genetics to steer the physical shape of a species.
It bridges the gap between dentistry, bone biology, and anthropology, perhaps answering the question as to why our jaws shrank before our brains grew.