This article is from WeChat official account:create (ID: xingshu100), author: He Miao (Fudan University brain Science Institute researcher), from the title figure: the movie” Ex Machina “
As the saying goes, “The country is easy to change, but the nature is hard to change.” As the saying goes, “the one near Zhu is red, and the one near ink is black.” …It sounds like these sayings each convey a strong point of view to people: Inheritance is very important, and the original family environment is very important.
Who decides more about people, genetics and environment? Why is there a big difference in personalities even for twins? Why do some people sing a song and become color blind when they look at things?
Why are people different from people?
Brothers and sisters who grow up in the same family look different, and even have different personalities;
We have been in contact with all kinds of people every day since we were young, but everyone seems to be different;
For people who are related or grown up in the same environment, which one has more influence on genetics or environment?
Why are people still different in the same environment and similar genes?
Research found that the differences between people are mainly reflected in differences in brain structure and function, which lead to differences in personality, perception, intelligence, and even the prevalence and severity of brain diseases.
What determines the difference in the brain
Where does the difference in the brain come from?
Scientists try to study this problem from two aspects.
First of all, in terms of physical characteristics, the answer seems to be very clear. We often feel that people who are close by blood generally look more similar. For example, children will look like their parents, and siblings will be more alike.
This feeling is consistent with the results of the experiment. Close kinship represents genetic information (DNA) more alike, so they look more alike. In other words, individual differences such as physical appearance are largely determined by differences in genetic information.
So what about character and intelligence? In addition to DNA inheritance, we often consider acquired environmental factors. To distinguish these two factors, scientists have adopted two research methods: adoption research and twin research.
First, assuming that genetic factors are the reason that people are similar or different in a certain way, then although the adopted child grows up in a different environment from his brothers and sisters, his personality should be similar to that of his relatives. The sisters are more similar. On the contrary, if he is more like his adoptive parents, it means that the acquired environment plays a major role.
Adoption Research
Second, twins can be divided into “identical” and “fraternal”. Assuming identical twinsThe fetus is A, their DNA similarity can reach almost 100%; the fraternal twins are B, their DNA similarity is similar to that of ordinary relatives, about 50%.
If A and B both grew up in their native families, then normally, the similarity in traits of identical twins A must be higher than that of fraternal twins B, but if an exception occurs, a trait of fraternal twins B is higher Identical twins A, it means that genetic factors have little effect here, similarity is caused by acquired environment, and vice versa means that genetics play a major role.
Twin study
After testing, scientists found that the similarity in the brain is the same as the results of behavioral and intelligence tests. Therefore, they use magnetic resonance imaging technology to compare the structure, connection, and function of the brain, and there are hundreds of related experiments.
The results all proved that people with more similar genetics have higher similarities in appearance and intelligence.
In other words, in terms of personality, intelligence, behavior, etc., a large part of the differences between people are controlled by genetic factors.
What makes you unique?
The German philosopher Leibniz said: “There are no two identical leaves in the world.” The same is true for people, even if they are identical twins, even if they are so similar, the characters displayed and the behaviors facing the same thing are never exactly the same.
What makes a unique self?
The similarity of genetic genes makes everyone different from others, but what ultimately determines the unique you?
To solve this problem, scientists introduced a concept—-Heritability, which is the percentage of DNA mutations that contribute to differences between people. After measuring various behaviors and abilities, the results show that heritability ranges from 30% to 80%.
For example, for example, the heritability of height is 60%, which means that some people are tall and some people are short. 60% of the phenomenon comes from DNA mutations, and 40% may be other factors.
In this case, how does DNA mutation cause it?
DNA mutation
DNA mutations are almost inevitable. Every time a cell divides and proliferates, DNA needs to be replicated, and replication will go wrong and form mutations.
Although there are many error correction and error checking mechanisms in our cells, they are still not 100% accurate. The reason is that the DNA of the genome is too long.
For example, the four masterpieces add up to almost 3.5 million characters. If each base of the genome is regarded as a Chinese character, then every time our human genome is copied, it is equivalent to copying the four masterpieces more than 800 times. , So it’s not surprising that there are occasional errors.
Mutated genes have repeatedly appeared, eliminated, eliminated and left in the process of human reproduction
Mutated genes have repeatedly appeared, eliminated, eliminated, and left in the process of human reproduction. Therefore, everyone has millions of mutant genes.
Scientists have conducted a lot of research and found that, for factors such as appearance, height, intelligence, and personality, genetic differences account for a relatively large amount, while environmental differences are relatively small.
This means that you are different from others because your genetics are not exactly the same; the reason you are what you are now is because DNA mutations played a big role.
Is there a rule for gene mutation?
The complex development process is full of the possibility of gene mutation. The development of an adult from a fertilized egg requires a series of very complicated steps under the guidance of genetic procedures.
In the earliest stage of embryonic development, the fertilized egg divides rapidly, one is divided into two, two is divided into four, and four is divided into eight, and so on, until a spherical embryo composed of thousands of cells is formed, and these cells will eventually develop into Different organs of the human body.
From a fertilized egg to an adult, you need to go through a series of very complicated steps under the guidance of genetic procedures
Take the brain as an example. It contains many different brain regions and tens of billions of cells, the number of which is comparable to the stars in the Milky Way. For these areas to form correctly, these cells must correctly arrive where they should be, perform the correct functions, and undergo a series of complex developmental processes.
If some key regulatory genes are changed, a certain structure may not be formed normally, which may lead to more serious developmental brain diseases. But even if the procedures are exactly the same, the process will still be affected by ubiquitous randomness.
Similar genes, will they still be similar after mutation?
Even if identical twins with almost identical genes, hairGene mutations in the breeding process are also full of probability problems, which are likely to lead to different final developmental results.
It’s like cooking. Even if there is a very detailed recipe, the tastes may still be slightly different from ten different chefs.
Many years ago, the famous developmental biologist Conard Waddington invented a visual metaphor to describe random processes in development and the way they lead to highly variable results.
In the picture, a small ball rolls down on an uneven terrain similar to a hillside.
Donald Waddington Theory
The small ball represents the organism in the development process, the top of the slope represents the initial fertilization, and the foot of the slope represents the possible outcome of development. There are various depressions and valleys on the hillside, and the ball may follow different paths to different ends.
When the ball rolls down, every time it encounters the starting point of the canyon, small random variations can affect whether it rolls to the left or right.
If you let the ball roll down 100 times to observe the result, it may enter a hypothetical canyon on the left 70 times and the right 30 times.
But these probabilities will vary from person to person, because the precise shape of each person’s “topography” reflects their own genome.
Left-handed or right-handed, although not entirely determined by genetics, it is still entirely congenital
Handiness, left-handed or right-handed, is a good example.
It is completely unaffected by the family environment, but it is only partly due to genetics. If one or both parents are left-handed, the chance of the child being left-handed will increase, but it will only increase the baseline from 10% to 15% or 20%.
The twin studies suggest that the overall heritability of this trait is only about 25%-identical twins are not usually left-handed at the same time. In other words, although this trait is not completely determined by genetics, it is still completely congenital.
Reading here, we seem to be able to draw such a conclusion: You = DNA+DNA mutation, is this statement correct?
In fact, this is not the full story of the story. Even if we combine “heredity” and “genetic mutation” together, it is still not enough to explain other mutations in the population. Is there a hidden third factor?
You=DNA+DNA mutation+?
What is this factor?
The first one may be the error of our measurement. For example, the same person fills in different dimensional scales and the results measured are different; today’s table and tomorrow’s table have different results, but in fact this part The error can be calculated, but after deducting this part, you will still find that there are still things that cannot be explained.
This leads to the second factor-non-shared environment, it does not refer to the day after tomorrowThe growth environment, but each of our experiences has some factors that are completely unique to the individual and not owned by others. They always make us more different.
Third, A more important source-not “environmental” factors, but internal factors inherent to everyone, derived from the randomness of the brain development process.
Why is the world that everyone sees so different?
The same song, why does someone sing it out of tune and someone is very accurate?
For the same painting, why does someone see 30 colors and someone sees 39 colors?
We seem to encounter situations like this often in our lives. Different people have different feelings about the same thing.
How many colors can you see in this picture?
For example, ask two people to answer how many different colors are on the same picture. If you count between 20 and 32, you may have three-color vision, which means that you have three different opsins. It can accept three different wavelengths of light: red, green and blue, and finally mixed together to form the colorful world we see.
But if you see less than 20 colors in this picture, it may be that the perception of one of the colors is missing, which is what we often call color blindness.
Some people may see between 32 and 39 colors. Then you may have a rare four-color vision. This is because there is a mutation in one of the three opsins that perceive color, which makes You have an additional ability to perceive colors, so you will see more subtle color differences.
This experiment description depends onFeeling is not like what you see is what you get with a camera, because the part of what we see, whether it is vision, touch or hearing, the stimulation we can feel is actually very monotonous.
For example, vision is the coming of photons, and hearing is the coming of sound waves, and the world we watch is very rich.
Therefore, perceptual ability is actually a concept formed by comparing and processing the information received from the outside world with the knowledge in one’s brain, and the cognition of the world.
Perception is an active process
In other words, perception is actually an active process. It is not just passively accepting an objective stimulus, and we immediately say what it is like, but by speculating on what exactly produces the sensory stimulus we feel , Such a behavior to achieve.
This means that the internal models that we have in our brains, the knowledge we have in our brains, can change the final result of how we feel the information.
From “receiving stimuli” to “forming perception” is a complicated process. In addition to mobilizing our external receptors, such as the retina, it also requires a series of neural circuits in the brain to process information.
Because the neural circuits are developed under the guidance of genetic programs, inheritance, gene mutations, etc. will affect the final perception result, and once there is a problem, it will also cause perception disorders. Such as color blindness, tone blindness, and face blindness.
Take tone deafness as an example. Why do people always sing out of tune?
If you measure this person’s perception of high and low sounds, you may find that he is actually very judgmental, but he can’t sing correctly. This situation is probably handled by his internal neural circuit. There was a deviation in the process.
Face blindness is the same. Some people don’t remember other people’s faces clearly, but recognize the wrong person.
He may not say that he can’t recognize this face and that face. If you put two photos objectively, he can see the difference, but he can’t compare this face with some other names about this person in his mind. , Occupation and other information are connected together.
In addition, there is also a special perceptual ability. It is not an error, but in some abnormal situations, a redundant connection between different feelings that should not exist. It is called “connection”. feel”.
character-color synesthesia
People with synesthesia will experience other extraneous sensations when receiving a single sensory stimulus, such as character-color synesthesia. They think that the strokes of letters, numbers or Chinese characters have natural colors.
According to the data of the American Psychological Association, only one synesthetist will appear in about 2000 people. Of course, this probability is higher among artists, writers and musicians, such as the founder of modern abstract paintingKandinsky.
Each unique me may not be perfect, but it is precious
Finally, we found that under the control of genetic programs, each individual has created a unique self in the world in a developmental process full of random and unrepeatable. It may not be perfect, but it is precious.
I hope that everyone can better understand themselves and others, and can see themselves and others more peacefully.
This article is from WeChat official account:create (ID: xingshu100), author: He Miao (Fudan brain Science Institute researcher)