Why is it so difficult to have children? Human evolution theory will give a reasonable answer

When we watch "Animal World", we often see the process of various animals giving birth. You must have had this feeling: it is so easy for these wild animals to give birth. Often, in just a few minutes, these mothers have completed the whole process of giving birth.

For example, chimpanzee babies are born in a very simple process, almost directly outside the mother's body, which can be said to be quite smooth. Compared with them, we humans seem a little weak. Giving birth is a huge challenge for women, especially in ancient societies where medicine was not well developed. Childbirth was an important cause of death for women.

Even today, when modern medicine has made great progress, childbirth is still considered a "dangerous" thing, and obstetrics is an extremely important part of clinical medicine. Childbirth, a normal physiological process, seems to be treated as a disease in modern medicine.

Image source: pixabay

Why are humans stuck in a fertility dilemma? Or, to put it more simply, why is it so difficult for humans to have children? This question can be given a reasonable answer from the perspective of evolution.

Everything starts with humans walking upright. For humans, walking upright can save more energy and free up the hands, making them more dexterous and more useful. But walking upright also brings a heavy burden to humans.

For animals that stand on four legs, stability is of course much stronger than that of humans who walk on two legs. When standing on four legs, animals can maintain a larger distance between their two hind legs, but this is not the case for humans. For humans who stand and walk on two legs, the greater the distance between the two legs, the worse the stability when standing.

Therefore, in order to maintain sufficient stability, during the process of evolution, the distance between human legs became narrower and narrower, and eventually reached the point where they could be brought together. This also means that the pelvis would not be too wide, and upright walking requires strong lower limb strength, which means that the muscles in the hips and legs need to become developed. As a result, the space within the narrow range of the pelvis becomes smaller and smaller.

For men, this does not cause any trouble, but for women who need to give birth, this poses a huge problem. During childbirth, it is very difficult for the fetus to pass through the birth canal. Every child needs to adapt to the different shapes of the pelvic planes and passively perform a series of adaptive rotations in order to be delivered smoothly. Only through such a complex method can the fetus be guaranteed to pass through the birth canal with the smallest diameter.

I will briefly describe the process of childbirth, including engagement, descent, flexion, internal rotation, extension, external rotation, fetal shoulder and fetal delivery. Hearing this, you can roughly understand how complicated it is.

Comparing the birthing process of chimpanzees and humans, we can clearly see how heavy a burden upright walking brings to mothers. However, from an evolutionary perspective, upright walking has given us humans unlimited possibilities. It is for this reason that from the moment our ancestors walked upright to today and into the foreseeable future, every mother has to bear the burden that evolution has brought us.

The article is produced by Science Popularization China-Starry Sky Project (Creation and Cultivation). Please indicate the source when reprinting.

Author: Sun Yifei, Director of the Medical Education History Research Office, Hebei Medical University

Reviewer: Chen Gang, deputy chief physician, Peking Union Medical College Hospital