Evolution & humans:big brain birth canal compared to fossils (Evolution)

by David Turell @, Saturday, September 21, 2019, 20:06 (62 days ago) @ David Turell

Studying our ancestors shows what was obviously known before. Birth was easy compared to human birth:

https://phys.org/news/2019-09-simulations-human-ancestors-easier-birth.html

"For many women, childbirth is a long, painful and difficult process. Prior research has suggested the reason childbirth is so much more difficult in humans compared to apes or other animals is because we evolved to walk upright, and because our babies have very large heads. As humans developed an upright gait, our pelvises changed in ways that made the birth canal narrower. During birth, a modern human baby must turn in the womb several times as it is pushed through the birth canal by the pelvic muscles.

"In sharp contrast, chimpanzees give birth in short order and appear to experience very little pain. In this new effort, the researchers wondered about the birth experience for one of our ancestors, Australopithecus sediba—a hominin that lived approximately 1.95 million years ago. To find out, they created a 3-D representation of an A. sediba pelvis using imagery from several fossils. While they were at it, they also created 3-D representations of Australopithecus afarensis and Homo erectus. And for additional comparison, they also created 3-D images of a modern human and a chimpanzee pelvis. To study the degree of difficulty of giving birth, the researchers also added baby human skull-sized objects to the 3-D images as they would normally sit in the birth canal.

'The researchers report that the size of the A. sediba birth canal was quite large compared to the size of the skull of the baby that would need to pass through it. They suggest this indicates that compared to modern women, A. sediba would have had a much easier time giving birth. "

Abstract:

"Hominin birth mechanics have been examined and debated from limited and often fragmentary fossil pelvic material. Some have proposed that birth in the early hominin genus Australopithecus was relatively easy and ape-like, while others have argued for a more complex, human-like birth mechanism in australopiths. Still others have hypothesized a unique birth mechanism, with no known modern equivalent. Preliminary work on the pelvis of the recently discovered 1.98 million-year-old hominin Australopithecus sediba found it to possess a unique combination of Homo and Australopithecus-like features. Here, we create a composite pelvis of Australopithecus sediba to reconstruct the birth process in this early hominin. Consistent with other hominin species, including modern humans, the fetus would enter the pelvic inlet in a transverse direction. However, unlike in modern humans, the fetus would not need additional rotations to traverse the birth canal. Further fetal rotation is unnecessary even with a Homo-like pelvic midplane expansion, not seen in earlier hominin species. With a birth canal shape more closely associated with specimens from the genus Homo and a lack of cephalopelvic or shoulder constraints, we therefore find evidence to support the hypothesis that the pelvic morphology of Australopithecus sediba is a result of locomotor, rather than strictly obstetric constraints."

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0221871#abstract0

Comment: All of this still raises the usual problem. How did the human pelvis and the large baby head evolve to allow a safe birth? The DNA of the mother and the father have to work with the DNA of The newborn. Only a planned design fits.


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