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. Molars that emerge “ahead of schedule” would do so in a space that, when chewed on, would disrupt the fine-tuned function of the entire chewing apparatus by causing damage to the jaw joint.įor 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. This delicate dance results in molars coming in only when enough of a “mechanically safe” space is created. Glowacka and paleoanthropologist Gary Schwartz, another Leakey Foundation grantee who is a researcher with the Institute of Human Origins and professor in the School of Human Evolution and Social Change, published their study this week that provides the first clear answer - it is the coordination between facial growth and the mechanics of the chewing muscles that determines not just where but when adult molars emerge. “One of the mysteries of human biological development is how the precise synchrony between molar emergence and life history came about and how it is regulated,” said Halszka Glowacka, lead author, Leakey Foundation grantee, and assistant professor at the University of Arizona, College of Medicine-Phoenix. Modern humans, for instance, grow up incredibly slowly, have a very long and protracted life history, and emerge their adult molars very late in life, later than any other living or extinct primate. For many decades, evolutionary anthropologists have leveraged the very tight relationship - which exists across all primates - between the pace at which these adult molars emerge into the mouth with the overall pace of life. The one dental feature intimately associated with the pace of growth and life history is the ages at which our adult molars cut through the gumline. Amazingly, clues to most of these components of our human biology are connected with our teeth. A key aspect of our biology allowing these components of the human experience to evolve is our unique “life history,” or the overall pace of life, including how fast we grow, how long we are dependent on mothers for nutritional support, how long it takes us to reach sexual maturity, and how long we live. We are highly intelligent, extremely social, remarkably resourceful, able learners, skilled teachers, and as a result, a remarkable evolutionary success story. Supported in part by The Leakey Foundaiton, Scientists at the University of Arizona and Arizona State University published a study in Science Advances this week that they think has finally cracked the case. Paleoanthropologists have wondered for a long time how and why humans evolved molars that emerge at these specific ages and why those ages are so delayed compared to living apes. These teeth come in at a much later age than they do in our closest living relative, the chimpanzee, who get those same adult molars at around three, six, and 12 years old. These are the ages that most people get their three adult molars or large chewing teeth towards the back of the mouth.
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