Given how critical brain growth is to early human development, and head size, in turn, influences the size of our jaws, researchers suspected teeth may hold some valuable information on our ancestors’ pregnancies.
Teeth begin to form at around 6 weeks of gestation but don’t develop their hardened exterior layers until the second trimester. From there, the growing layers can retain records of their life history, from weaning to sexual activity.
“Dental remains are the most abundant parts in the fossil record,” explains paleobiologist Leslea Hlusko from the Spanish National Research Center for Human Evolution (CENIEH) making teeth an ideal candidate for sussing out such biological mysteries, if a relationship between them and the process in question can be established.
Both cranial and dental remains indicate that prenatal growth rates increased over the last 6 million years. Along with fossilized pelvis and head anatomy, these findings support the theory that long human-like pregnancies evolved within the last few hundred thousand to million years, during the Pleistocene.
As primates transitioned to walking on two legs in the Early Pliocene around 5.333 million years ago, signs of which were starting to be visible in Australopithecus and Ardipithecus fossils, their prenatal growth rates were still more similar to the monkeys and apes alive today, than to ours.
