Human Birth Canals Evolved Into a Twisted Form for a Purpose, Study Says

One aspect of physiology is responsible for making the birth of humans distinct from other species. The process of giving birth to offspring may seem simple, but in fact, it comprises biological complexities that are unique to the collective birth deliveries. A new study was able to identify this one-of-a-kind method through the use of gait and posture biomechanical modeling.

The Complexities of Human Birth

Human Birth Canals Evolved into a Twisted Form for a Purpose, Study Says

(Photo: Jonathan Borba from Pexels)

The human birth canal has a narrow opening that, at first observation, may seem for a whole embryo to go through. The ability of the canal to stretch is an effective factor to provide comfort and protection to the human baby inside. It also has a kinked area at the inlet that is naturally utilized by the contractions for an effective rotation of the embryo that measures 90 degrees upon fitting in the pelvis region. If the process makes the baby stuck in a different direction, it may risk the health and lives of both the parent and offspring. The misdirection of this natural rotation occurs for 6 percent of the global births recorded.

Even though humans have seemingly perfected the developmental stages of pregnancy and birth delivery, there are still some fragments of the puzzle unexplored by modern biological studies. Among the mysteries of human birth is why mothers must go through meticulous and time-consuming labor, while other species could freely eject their offspring without minimal to no effort.

The human pelvis is a shape that adapted throughout evolutionary history for a better walking experience. But not every human has a fitting pelvis shape for the advantage of walking or giving birth, as many individuals still obtain less-than narrow hips and other challenging conditions.

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Evolution of the Human Birth Canal

The new study contrasts all of the previous theories about the human pelvis. Through biomechanical models of pelvic floors, the latest research implies that the birth canal's corresponding shape does not help people walk more than it could assist us in standing up.

University of Vienna's Department of Evolutionary Biology expert and author of the study Phillipp Mitteroecker said in a Science Alert report that the human pelvic inlets evolved due to the challenge of the anatomical body, specifically the front-to-back diameter that is responsible for the upright posture. This idea is polar to the first thought theory on bipedal locomotion.

Mitteroecker said that the baby could slide through the womb up to the birth canal if the inlet came in a deeper oval shape. This process is observed in other primate species. However, humans do not have this ability. The embryo must be tilted by the pelvis significantly than its current position, which contributes to a deeper curve manifesting on the lower back of the torso.

But as confusing as it appears, the extra curve identified is essential to maintain the health and structure of the spine, and this could also be the reason why the birth canal's opening diverted into a new physical form. The study was published in the journal BMC Biology, titled "The evolution of pelvic canal shape and rotational birth in humans."