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Scientists have come up with a new theory about gestational age
Medical expert of the article
Last reviewed: 01.07.2025
A newborn human baby is born less developed in terms of motor and cognitive abilities than the babies of other primates.
For a long time, scientists explained this by relying on the main distinguishing feature of humans - the size of the brain. A large brain requires a large head, which can hardly pass through the birth canal. Therefore, according to scientists, nature shortened the duration of human pregnancy so that the baby would be born before its head became too large for normal birth. As a result, the child is born practically helpless.
A longer pregnancy to give birth to a more developed baby would have been possible if women had a wide enough pelvis, but scientists assumed that in this case, humans, as upright animals, would not have been able to move normally. However, Holly Dunsworth, a professor at the University of Rhode Island, doubts the validity of this explanation, as well as the entire generally accepted theory outlined above.
Taking into account the mother's body size, human pregnancy lasts even a little longer and newborn babies are somewhat larger than those of other primates.
The professor wondered whether metabolic processes in the body of expectant mothers could explain the timing of human pregnancy.
Dunsworth teamed up with physiology expert Peter Allison of Harvard University and Herman Pontzer of Hunter College to study the issue.
Scientists have developed a new hypothesis about the duration of gestation in the mother's womb.
"Our theory is that babies are born when they are born because at that point the mother no longer has the energy to support the embryonic development of the baby. The mother's energy is the main evolutionary constraint, not her hips," Dunsworth says.
"Our bodies can burn a limited number of calories each day," Pontzer explains. "During pregnancy, a woman reaches that limit, and the baby is born before that limit is exceeded."
This process, driven by the mother's metabolism, explains why infants are helpless compared to our primate cousins.
Another argument that the experts made in favor of their theory was an anthropological study, based on which they concluded that the male pelvis is more suitable for childbirth than the female one.
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