There’s a weird connection between teeth and the evolution of pregnancy: ScienceAlert

Human babies grow a lot in those nine months between conception and birth to give them and their fleshy, complex brains a chance to survive.

How evolution gave humans such a relatively fast prenatal growth rate has never been clear.

Given how crucial brain growth is to early human development, and head size in turn influences the size of our jaws, researchers suspect that teeth may hold valuable information about our ancestors’ pregnancies.

Teeth begin to form at about 6 weeks gestation, but don’t develop their hardened outer layers until the second trimester. From there, the growing laying hens can track their life history from weaning to sexual activity.

“Tooth remnants are the most abundant parts in the fossil record,” explains paleobiologist Leslea Hlusko of Spain’s National Research Center for Human Evolution (CENIEH), making teeth an ideal candidate to solve such biological mysteries, if there is a connection between them and the process in question can be determined.

Ultrasound of a human at a gestational age of 26 weeks. (Tesla Monson/CENIEH)

The team’s previous research in monkeys found slower growth of an unborn animal and lack of development of the third molar. to obtain the relative molar size.

They found that prenatal growth rate, head size and relative molar size indeed all followed the same pattern in all of these primates. So they used this established pattern to delve into our evolutionary history, analyzing primate fossils from 6 million to 12,000 thousand years ago, spanning 13 hominin species.

Five skulls of different primate species.
Youthful Australopithecusgrown up Australopithecusadult chimpanzee, juvenile chimpanzee and adult Homo erectus (Centre). (Tesla Monson/UO Museum of Natural and Cultural History/CENIEH)

Both skull and tooth remains indicate that prenatal growth has increased over the past 6 million years. Together with the fossilized anatomy of the pelvis and head, these findings support the theory that long hominid pregnancies developed over the past several hundred thousand to million years, during the Pleistocene.

When primates transitioned to walking on two legs about 5.333 million years ago in the early Pliocene, evidence of which began to appear in Australopithecus and Ardipithecus fossils, their prenatal growth rates were still more similar to the monkeys and apes living today than to ours.

But due to the evolution of Homo erectus in the early Pleistocene, about 2,580,000 years ago, there was a marked shift, which was also reflected in their pelvic anatomy.

“Changing pelvic anatomy, endocranial volume, and predicted prenatal growth rates all provide independent lines of evidence supporting hominin gestation and birth that evolved in the Pleistocene into the later Homo genus, before the emergence of homo sapiens”, writes the team in their newspaper.

These changes coincide with the expansion of grasslands and herbivore populations, which may have contributed to the cause Homo sex with the extra resources needed to fuel the increase in neonatal size and longer maternal investment.

Improvements in tools that also occurred during this time may reflect the growing brain size of our ancestors, as well as the likely evolution of pack hunting, which in turn would have provided even more resources.

“This feedback loop, in turn, may have allowed for the evolution of even larger brains and, later, greater cranial capacity Homolead to H. sapiens”, concludes the team.

This research was published in PNAS.

Leave a Reply

Your email address will not be published. Required fields are marked *