The shorter and wider repositioning of our pelvic leaves makes it easier for humans to walk or balance than chimpanzees and gorilla .
A new study shows how the pelvis evolves to walk upright.
If evolutionary biologist Terence D. Capellini ranks the parts that define us as humans, the pelvis will face the top.
After all, thanks to its design, humans can walk upright on two legs (unlike our primate cousins), and mothers can give birth to children with huge heads (and therefore large brains). The pelvis is well understood on anatomy , but our understanding begins to shake when it comes to how and when this very basic structure forms throughout development.
This is changing due to recent research by Capellini's team. The study, published in the journal Science Advances , shows when the pelvis forms during pregnancy and determines the genes and gene sequences that drive this process. This study may one day gain insight into the genetic origins of bipeds and pave the way for the treatment or development of predictive factors for hip diseases such as hip dysplasia and hip osteoarthritis.
"This paper really focuses on what all humans have in common, namely these changes in the pelvis that allow us to walk on two legs and allow us to give birth to a large fetal head," said Capellini, a new professor in the Department of Human Evolutionary Biology at Harvard University and senior author of the study.
studies show that many of the characteristics necessary for human walking and childbirth form around 6 to 8 weeks during pregnancy. This includes key pelvic features unique to humans, such as their curved and basin-like shapes. Formation occurs when the bones are still cartilage, so they can bend, rotate, expand and grow easily.
researchers also found that when other cartilage in the body begins to transform into bones, the developing pelvic area remains in cartilage for longer periods of time, allowing it to mature normally.
"It seems like a stall occurs, which makes the cartilage still grow, which is very interesting and surprising," Capellini said. "I call it a protected area.
researchers used RNA sequencing to determine which genes in the region are actively triggering pelvic formation and slowing ossification, which usually converts softer cartilage into hard bones. They found hundreds of genes that open or close in 6 to 8 weeks to form the iliac in the pelvis, which is the largest and uppermost bone of the hip joint, has a leaf-like structure that bends and rotates into a basin to support two legs walking.
The shorter and wider repositioning of our pelvic leaves compared to chimpanzees and gorillas allows humans to not have to move their weight forward, but use our knuckles to walk more comfortably or balance. It also helps increase the size of the birth canal. . On the other hand, the birth canal of apes is much narrower and the iliac bone is longer.
researchers started this study by comparing these differences in skeletal samples of hundreds of humans, chimpanzees and gorillas. These comparisons show the surprising effect of natural selection on the human pelvis, especially the iliac bone.
To observe when the ilium and pelvic elements that form the birth canal begin to take shape, the researchers examined embryos 4 to 12 weeks under a microscope with the consent of people who legally terminated their pregnancy. The researchers then compared samples from the developing human pelvis with a mouse model to determine the switch that triggers formation.
This work was conducted by Mariel Young (Mariel) Young, who is a former graduate researcher at Cappelini Labs, graduated in 2021 with a Ph.D. The study is a collaboration between Cappelini Labs and 11 other labs in the U.S. and around the world. Ultimately, the team hopes to understand what these changes mean for common hip diseases.
"Walking with two legs will affect the shape of our pelvic body, which will affect our future risk of disease," Capellini said. "We want to reveal this mechanism. Why does the choice on the pelvis affect our late disease risk in hip , such as osteoarthritis or dysplasia? It would be crucial to establish these connections at the molecular level.
