A study discovers a surprising relationship between teeth and the evolution of pregnancy

Humans have the highest prenatal growth rate of any existing primate, but how this exceptional rate came about has been a mystery until now. Leslea Hlusko, a scientist at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), participated in a study led by Tesla Monson, a paleoanthropologist at Western Washington University (WWU) in the United States), looking at teeth, prenatal growth rates, and the evolution of pregnancy. This research has uncovered a key piece of this puzzle in an unexpected place: the relative sizes of fossilized molars.

The teeth are indicators of what’s happening elsewhere in the body, and this study, published in the journal Proceedings of the National Academy of Sciences (PNAS)shows that they can be used as a map to unravel the effects of the interplay of genetics and development, and to improve our understanding of the history of life in the past.

Tesla Monson and her team, including Andrew Weitz, of WWU’s Department of Environmental Sciences, scientists at the Berkeley Geochronology Center (USA) and CENIEH, have studied fossils of the primate group, including the apes and monkeys of the Old World. as well as data compiled from fossilized molars and skull fragments from the terminal Miocene to the Plio-Pleistocene period, ranging from about six million to about 12,000 years ago.

The results indicate that the humanoids achieved a prenatal growth rate that set them apart from all other apes between a million and a half million years ago, long before the human species evolved itself (between 300,000 and 200,000 years ago).

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The prenatal growth rate is closely related to the endocranial volume and surprisingly to the variation in the proportions of the molars. “This shows that the teeth can be an indicator of both prenatal growth rate and brain size, which is of particular importance for our ability to study the gestational development of our human ancestors, as tooth remains are the most abundant parts in the fossil recordHlusko says.

This discovery of the relationship between the proportions of the select and prenatal growth rates have raised many new questions for evolutionary researchers, such as understanding the underlying genetic mechanisms. Another important question is whether this also occurs in other mammals.

“While I don’t think our humanity can be reduced to the teeth alone, I do believe some of it is captured in our teeth. This work opens a window for studies of pregnancy and pregnancy. We can take dental material from human ancestors and other fossils primates to find out what their pregnancies were like,” concludes Monson.