Zhuang Shili and

Doctor

A senior medical consultant from Shengnuo

Master of Neuroscience from Hokkaido University

In ancient China, fortune tellers often help to determine whether to have boys or girls, and directly put up a signboard: "No money"!

and the quotations of these fortune tellers are often expensive, ranging from hundreds to tens of thousands.

For example, if you predict to have a boy, you will receive 18, yuan. If you win the prediction, the whole family will be happy. You can boast that Mr. Zhi is a contemporary Yuan Tiangang and a near-re-embodiment millet. Maybe you can give him a big red envelope.

and the prediction is wrong, some people think about it and repeat the slogan of family planning propaganda: boys and girls are the same, and daughters are more filial to their fathers and mothers; Some people who don't know what's good or bad want to get a refund from Mr. Wang, but they didn't expect to call Mr. Wang a scolding-this is God's will, so how can it be artificial!

As a medical student in the new era who has been studying biochemistry since high school, he can certainly see through the fortune teller's trick at a glance: the probability of having boys and girls is obviously 1:1. Suppose 1 fortune tellers come to tell fortune, half of them have boys and half of them have girls, and fortune tellers all bet on men. In the end, men will make a steady profit and women will get a refund. It's a lucrative business!

However, today, I want to tell you a serious fact:

The probability of having boys and girls is the same, which is actually a wrong understanding. Under natural conditions, the birth probability of boys is higher than that of girls.

as shown below, this is the ratio of male to female newborns in OECD countries.

Why are there more treasures?

Scientists have had a long and fierce debate on this issue.

Shettles theory

in 196, an American biologist named Landrum Shettles took the lead in putting forward a conjecture.

We know that the baby's sex has been determined at the moment when X or Y (hereinafter referred to as X or Y) is combined.

so, is it because y is easier to combine with?

Y is smaller than x, so y is light, and the smaller it is, the faster it runs, so y swims faster and can be combined earlier.

According to this theory, Shettles and his friend * * * later created a theory called Shettles to help parents choose the sex of their children.

This theory holds that Y runs fast, lives short and is easily influenced by acidity, so the closer the insemination time is to ovulation time, or it will be released closer to the mouth (where the acidity is less than the outside), the more likely it is to have a boy; If you want to have a girl, do the opposite.

Shettles' theory is widely spread. The "Millennium Ancestral" technique circulating in China today, as well as the theoretical viewpoints in many health-preserving bestsellers, and even the acidic physique theory with a very broad mass base in the circle of friends, are actually influenced to some extent by Shettles' theory.

Shettles theory is

However, many doctors and scientists in the United States do not trust Shettles theory.

In 1995, American epidemiologist James Wilcox studied 221 women for a long time, and recorded more than 6 ovulation cycles, and recorded the date and date of their couple in detail.

The research results show that almost all pregnancies are attributed to the time difference between the next six days and the term, which has nothing to do with the baby's sex.

This study was later published in NEJM (New England Medicine), which is a rigorous study of Shettles' theory.

that's not enough. with the rapid development of computer technology, in 1998, researchers used computer-aided analysis technology (CASA) to observe the movement more accurately.

The results show that although X carries more DNA than Y, Y and X are the same in terms of movement speed. The only difference is that the linear degree of their movements is different.

Moreover, there is no difference in their ability to combine. In fact, at the first moment of life, the ratio of male to female is extremely close to 1:1.

Then the question comes, when the ratio of male to female is the same, why are there more treasures at birth than female babies?

where did the baby girl go?

In the past, academia always thought that men were more vulnerable than women from a physiological point of view.

For example, the average life expectancy of men is lower than that of women. You are like China with the longest life expectancy in the world (yes, it has surpassed Japanese). The average life expectancy of men is 81 years, while that of women is as high as 87 years.

For example, the incidence of almost every kind of cancer is higher in men than in women. Some cancers may differ by only a few percentage points, while some cancers are even 2-3 times higher for men than for women.

however, before birth, the situation may be different.

In 222, the team of Steven Orzack, an American biologist, conducted a larger and most comprehensive study on the sex ratio of the fetus at birth.

Contrary to popular belief, female fetuses are actually more fragile.

It is found that the mortality rate of male and female fetuses is constantly changing at different stages.

At present, the proportion of male embryos is the same as that of female embryos; < P > In the first two weeks after birth, the male embryo death rate is high at this time, and the male ratio begins to be lower than .5;

After 1-15 weeks, because the mortality rate of female fetus is higher than that of male at this time, the proportion of male increased by more than .5, and this trend continued until the 2th week.

After 28 ~ 35 weeks, the male fetal mortality rate increased again, and the male ratio began to fall back until it was close to .5, but it would not be lower than .5.

Contrary to what many of our textbooks have said in the past, this study with a sample size of nearly one million found that in fact, the primary sex ratio of human beings has almost no tendency. Throughout pregnancy, the mortality rate of female fetus is higher than that of male fetus.

The specific reason is still unclear. The only thing we can know at present is that it may be related to No.15, No.17 and No.17. This alternate change in fetal mortality eventually led to more treasures at the moment when they came out of the womb.

this study was later published in PNAS. This study has studied some inherent viewpoints in textbooks, and the more far-reaching significance of this study is that it shows that even today when medicine is so developed, we may still have some wrong understandings of those things about human beings.

Whether it is determined by human genes or arranged by nature, under the influence of various coincidences, most of them are born with slightly more boys.

However, due to men's aggressive nature and their susceptibility to some diseases, by the age of 2, the mortality rate of men is higher than that of women, which shows the balance of nature.

Zhihu ID: Zhuang Youmao

Master of Hokkaido University

Editor Bruce

Zhuang Shili and

Typesetter Xiao Xuanxuan Smile

The above is the content of calculating the numbers of men and women with the previous child, which is about the sharing of fortune tellers. It's so accurate after reading it! After seeing men and women, I hope this will help everyone!