Why the human body has not evolved to make childbirth easier — or has it? 為什麼人體沒有進化來使分娩更容易-還是讓分娩變得容易？

News Release 22-Apr-2021

Editor’s note: God design it that way. As explained in the report, there is a reason for this mechanism. We need to understand that the way God create is the best you can imagine. Human body is full of wonders which are indeed signature of God’s work.

Just for the fun of it, ever try to think how an adult man regulates the sperm-making, and how his sperm finds their way to fertilize an egg that is even located remotely, and once the egg accepts the sperm, it will automatically shut the door to other sperm. This establishes the one to one relation between a sperm and an egg leading to forming a viable embryo. All these processes reflect the logic and intelligence of the creator.

編者註：上帝是那樣設計的。 如報告中所述，有這種機制的原因。 我們需要了解，上帝創造的方式是您可以想像的最好的方式。 人體充滿著奇觀，這些奇觀確實是上帝工作的標誌。 只是為了好玩，請嘗試思考一個成年男子如何調節精子的產生，以及他的精子如何找到使甚至位於偏遠位置的卵子受精的方法，一旦卵子接受了精子，它就會自動關閉 其他精子的門。 這在精子和卵之間建立了一對一的關係，導致形成了可行的胚胎。 所有這些過程都反映了創作者的邏輯和智慧。

University of Texas at Austin

Research News

AUSTIN, Texas — Despite advances in medicine and technology, childbirth isn’t likely to get much easier on women from a biological perspective.

Engineers at The University of Texas at Austin and University of Vienna revealed in new research a series of evolutionary trade-offs that have created a near-perfect balance between supporting childbirth and keeping organs intact on a day-to-day basis. Human reproduction is unique because of the comparatively tight fit between the birth canal and baby’s head, and it is likely to stay that way because of these competing biological imperatives.

The size of the pelvic floor and canal is key to keeping this balance. These opposing duties have constrained the ability of the pelvic floor to evolve over time to make childbirth easier because doing that would sacrifice the ability to protect organs.

“Although this dimension has made childbirth more difficult, we have evolved to a point where the pelvic floor and canal can balance supporting internal organs while also facilitating childbirth and making it as easy as possible,” said Krishna Kumar, an assistant professor in the Cockrell School of Engineering’s Department of Civil, Architectural and Environmental Engineering who led the research published this week in the journal Proceedings of the National Academy of Sciences.

The pelvic floor in women is a band of muscles that stretches across the bottom of the abdomen from the tailbone to the pubic bone. It supports pelvic organs, including the uterus, bladder and bowel, and it helps stabilize the spine.

A larger pelvic floor and canal would facilitate easier childbirth. But the larger it becomes without additional bones or tissue to support it, the more likely it is to deform under the weight of organs and cause them to fall downward.

These trade-offs, referred to as the pelvic floor hypothesis, were known in the scientific community. But the theory had been difficult to test until this research team used engineering tools to investigate it.

Kumar first started thinking about the problem by comparing the pelvic floor to a trampoline. A bigger trampoline will drop further as weight is applied, whereas a smaller trampoline will hold its structure better.

In addition to studying the size of the pelvic floor, the researchers also looked at thickness. In theory, a thicker pelvic floor could continue to support organs and an expanded size for childbirth. But it did not turn out that way.

“We found that thicker pelvic floors would require quite a bit higher intra-abdominal pressures than humans are capable of generating to stretch during childbirth,” said Nicole Grunstra, an affiliated researcher at the University of Vienna’s Unit for Theoretical Biology in the Department of Evolutionary Biology. “Being unable to push the baby through a resistant pelvic floor would equally complicate childbirth, despite the extra space available in the birth canal, and so pelvic floor thickness appears to be another evolutionary ‘compromise,’ in addition to the size of the birth canal.”

The team got to this conclusion by applying principles common in civil engineering. Kumar used a Finite Element analysis, a computerized model often deployed to test the design of structures to see whether they will break or wear down when facing high levels of pressure and stress. In this case, Finite Element analysis allowed the team to model the pelvic floor, change its parameters and see how it responds to the stresses of childbirth and protecting organs, which is otherwise impossible to test using clinical data.

This is the first time Finite Element analysis has been used to explore an evolutionary question. However, it isn’t the first time Kumar has applied engineering tools to biology.

While at the University of Cambridge in the U.K., where he met his co-authors who are now at the University of Vienna, Kumar applied a transportation analysis technique to herpes to learn more about how it first spread among humans.

This collaboration shows that engineering approaches and tools are relevant to important problems that, at first glance, may seem well outside the discipline, said Kumar, whose primary research involves numerical models for earthquakes, landslides and other disasters.

“You can abstract all the biology away, and it comes down to what happens if you apply stress, what does it do to bodies and structures with different material properties,” Kumar said. “If you squint your eyes, a large landslide can look like a pelvic floor.”

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