Birth of children is an animal physiological instinct of human beings. Human reproduction and evolution are guaranteed by the continuation of future generations. "Ten months of pregnancy, one day of childbirth" is the natural reproduction law of the human body.
But humans are the only creature on earth that will cause difficult labor. Even if there is no difficult labor, the pain and danger of human childbirth are the highest among all living things. For most animal mothers, childbirth is an easy thing, just like a hen laying an egg.
In fact, according to the excavated fossils, humans were already facing the dilemma of childbirth at least 3 million years ago. Why did this happen? Scientists' research results show that this is the price of human women walking upright.
In order to walk upright, the pelvic structure changes in human women
Most animals have narrower heads than maternal birth canals, so there are usually no difficulties in animals for delivery. In order to gain higher intelligence, humans have evolved and become larger and larger.
. In order to walk upright, the pelvic structure of human women also changed. The pelvic belt of primates consists of three main parts: blade-shaped bones, called iliac , which extends outwardly to form the buttocks. There are two tubular fusion bones below the ilium, called pubic and ischial , which form the birth canal. The ilium of the ape is relatively long and can lie flat on the back of an animal, and the birth canal is relatively narrow. These pelvic patterns have appeared among early human ancestors, such as the 4.4 million years ago, who had slightly longer ilium bones and were thought to walk on at least occasionally with two feet.
Compared with the apes, the human ilium is shorter and more rounder, curved and concave to the left and right sides of the body, and has begun to have a bowl-like structure. is very beneficial for support and muscle growth. The human-remodeled ilium provides attachment points for muscles, which can fully carry our weight. Make walking upright more stable.
In addition, the upper and lower diameters of the human pelvis are reduced, the ligaments are strengthened, the anterior and posterior walls approach each other in the vertical direction, and the female birth canal also becomes narrower. In addition, humans are originally big-headed babies, so it is very painful and dangerous for human women to have children.
pelvic structure changes also make the birth canal of human women narrow and distorted. Generally speaking, the upper part or entrance of human women's birth canal is round and transverse (from left to right) elliptical, which is considered an ideal situation for childbirth, but the lower part of human women's birth canal is obviously longitudinal (from front to back) elliptical. This twisted structure usually requires the fetus to rotate its body when it passes through the narrow birth canal.
In order to adapt, human babies are born prematurely
In fact, in order to reduce the risk of mother giving birth, human babies are born prematurely. Humans need to raise babies until they are over 1 year old, and their development level is similar to that of newborn chimpanzees. Therefore, scientists believe that human babies need to develop in their mother's belly for 18-21 months before they can be considered mature, which is also true full-term .
But if the baby develops in the mother's belly for 18 months, it will definitely not be born. In fact, human women have worked hard to evolve to increase the opening of the pelvic opening to adapt to the enlargement of the baby's brain; however, the enlargement of the pelvic opening is limited, and it is restricted by the movement method of walking upright on both feet; when the brain volume of the newborn is 385 ml (about 1/3 of that of an adult), the opening of the human pelvic opening has actually reached its limit, so this is why human babies have to give birth after ten months of pregnancy.
In addition, in order to pass through the birth canal, the bone septum of human babies is delayed, we can see that some babies have their heads deformed after passing through the birth canal, but it doesn't matter, because the bone septum of the baby is not healed.
The metapic suture also forms a frontal midline, dividing the frontal bone into two parts, from the root of the nose to the coronal seam. When the young child is about two years old, the forehead seam heals from the root of the nose, and splicing the two parts of the frontal bone like a zipper.From newborn to adulthood, the human brain volume has doubled.
The size of the brain is not only related to intelligence, but also to important events in life history, such as the age of weaning, age of sexual maturity, pregnancy and lifespan. Compared with animal species with smaller brains, the associated species with larger brains have a later weaning period, a later sexual maturity, a longer pregnancy period, and a longer individual lifespan.
The human growth cycle is unique
It is precisely because human babies do not develop enough time in the mother, so the human growth cycle is also unique. Compared with other animals, babies are weak and helpless when they are just born from the mother (because they have not developed full term). Growing up, they have to go through a longer period of childhood and then through a puberty with a sudden acceleration in growth, at which time their height grows at an alarming rate. Among the existing mammals, this phenomenon occurs only in humans; most mammals, including apes, enter almost directly from infancy to adulthood.
In summary, in order to gain the ability to walk upright, human women have changed the pelvic structure, and the sequelae is that they will face difficulties in childbirth. In order to adapt to the changes in the pelvic structure of human women, human babies have also made their own changes.
In fact, after humans stand up and walk upright, the most obvious result is to liberate the forelimbs, including their hands. This gradually formed labor. Gradually, the division of labor in human society formed a model in which men went out to hunt or gather food, and women stayed at home to take care of their children, greatly improving the survival rate of human offspring. It can be said that walking upright is the basis for human civilization.
