The evolutionary history of pregnancy seen in teeth?

Humans have the highest prenatal growth rate of any primate living today, but the evolution of this high prenatal growth rate has been a mystery, until now.

A team made up of, among others, Leslea Hlusko, a scientist at the National Center for Research on Human Evolution (CENIEH) in Spain, and Tesla Monson, a paleoanthropologist at the Western Washington University (WWU) in the United States), has carried out a study on teeth, prenatal growth rates and pregnancy outcomes that has revealed a fundamental piece of this puzzle in an unexpected place: the relative sizes of fossilized molar teeth.

The teeth are indicators of what happens in other parts of the body and in this study, published in the academic journal PNAS (Proceedings of the National Academy of Sciences), it is shown that they can be used as if they were a map that helps to navigate the labyrinth involving the intertwined effects of genetics and development, as well as to better understand the history of life in the past.

Hlusko, Monson, and their colleagues analyzed fossils of the primate group that includes apes and monkeys from Africa and Asia, as well as data collected from fossilized molars and skull fragments from the Late Miocene to the Plio-Pleistocene epochs, a few years ago. 6 million years to about 12,000 years ago.

The results indicate that hominids reached a prenatal growth rate that separated them from other apes between half a million and a million years ago, long before evolution led to the appearance of the human species as such, between 200,000 and 300,000 years.

Homo erectus, Homo sapiens and Australopithecus skulls. (Image: Museum of Natural and Cultural History – University of Oregon / Tesla Monson)

Prenatal growth rate is closely related to intracranial volume and, surprisingly, to variation in molar tooth proportions. “This shows that teeth can be an indicator of both prenatal growth rates and brain size, which is especially important for us to study the gestational development of our human ancestors, since dental remains are the most abundant parts. from the fossil record,” says Leslea Hlusko.

This discovery of the relationship between molar ratios and prenatal growth rates has raised many new questions for evolutionary researchers, including understanding the genetic mechanisms behind this relationship. Another key question is whether this relationship also occurs in other mammals.

“Although I don’t believe that our humanity is reduced only to our teeth, I do believe that part of it is recorded in our teeth. This opens a window for the study of pregnancy and gestation. We can take dental material from human ancestors and other fossil primates to find out what their pregnancies were like” concludes Tesla Monson. (Source: CENIEH)