Variation In The Shape of the Human Birth Canal

The common understanding has been that the shape of a human mother's birth canal has been fashioned by the evolutionary forces that it needs to be wide enough to allow large brained babies to pass through but narrow enough for women to walk efficiently. This evolutionary compromise is known as the obstetrical dilemma. Research by biological anthropologist, Lia Betti, and evolutionary ecologist, Andrea Manica, challenge the obstetrical dilemma. The obstetrical dilemma would suggest that birth canal shape around the world would be relatively standardized but the findings of these researches did not support this. Betti and Manica measured the pelvises of 348 female human skeletons from 24 different parts of the world. They found women from sub-Saharan Africa and some Asian populations has pelvises that were narrow from side to side and deep from front to back. They found that Native American women had wider canals and that Native Americans and Europeans had the most oval-shaped upper canals. They saw that there was less variability in shape in populations farther from Africa.  Their analysis proposed that the variable shapes were due to neutral evolution through genetic drift and migration.  They hypothesized that climate could have contributed to different shapes however they found little evidence for it and suggest further research into other ecological factors.  Betti and Manica said their research could be important for modern obstetric practice in multi-ethnic societies as modern medical understanding is developed mainly on studies of European women.

https://www.sciencemag.org/news/2018/10/birth-canals-are-different-all-over-world-countering-long-held-evolutionary-theory
http://rspb.royalsocietypublishing.org/content/285/1889/20181807

Maeve Curran