Paleoanthropologists have wondered how and why humans evolved molars that emerge into the mouth at specific ages and why those ages are so delayed compared to living apes. Scientists at the University of Arizona and Arizona State University found that adult molars are emerged due to the coordination between facial growth and the mechanics of the chewing muscles. The adult molars are determined to erupt only when enough of a "mechanically safe" space is created to prevent the damage of the jaw joint.
For the study, Glowacka and Schwartz created 3D biomechanical models of skulls, including the attachment positions of each major chewing muscle, throughout the growth period in nearly two dozen different species of primates ranging from small lemurs to gorillas. When combined with details about the rates of jaw growth in these species, their integrative models revealed the precise spatial relationship and temporal synchrony of each emerging molar within the context of the growing and shifting masticatory system.
The researchers plan to apply their findings to fossil human skulls to answer questions about when slowed jaw growth and delayed molar emergence first appeared in our fossil. The study could also help understand the phenomenon of impacted wisdom teeth in humans.
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