"Big Head Son Little Head Dad" is a childhood memory for many people. There has always been a rumor that "the bigger the head, the smarter the smarter", is it really that the person with the big head is smarter?
A large brain volume does not necessarily equal high intelligenceFrom the perspective of human evolution, it seems that "the bigger the brain, the smarter".
For example, the brain volume of modern chimpanzees is only 420 milliliters, while the average brain volume of modern humans is 1350 milliliters. Lucy, a hominid who lived in Africa more than 3 million years ago, had a brain size of only about 400 milliliters. When Homo erectus appeared 2 million years ago, the brain volume increased to 800 milliliters. It seems that brain volume increases with the development of human intelligence.
Human evolution based on the skull casts of ancient primate and early hominid fossils, with the abscissa showing the age and the ordinate showing the brain volume
Source: Popular Science China
On the surface, a large brain capacity can accommodate more neurons, and the natural intelligence will be relatively high. But if we look a little wider and look at other animals, we find that this statement is not entirely true.
For example, the brain of a cow (about 440 grams) is more than 200 times heavier than the brain of a mouse (about 2 grams), which is about the same as that of a chimpanzee. But cows are not only far less intelligent than chimpanzees, they are no smarter than mice. Even if they are also dogs, huge dogs are sometimes not as smart as small dogs. With a brain weighing only 10 grams, the crow is one of the most intelligent birds.
不同脊椎动物的大脑（引自Miller and Harley 2001）
Large brain volume does not necessarily equate to high intelligence. Larger animals also tend to have larger brain volumes. But these "extra" neurons are not necessarily used to improve intelligence, but first to satisfy the control and management of the large body. To understand the relationship between brain mass and body mass and the impact of this relationship on intelligence, Dutch anatomist Eugene Dubois and his colleagues collected brain and body mass from 3,690 animal species. His successors analyzed the data and found that as the animal's body grows larger, the mass of the brain does not increase proportionately, but to the power of 0.7~0.8 of the body weight, that is, about 3/4 power. For example, the body weight of a muskrat is 16 times that of a mouse, but the brain weight of a muskrat is only 8 times that of a mouse. By inputting these body mass and brain mass into logarithmic coordinates, the abscissa is the body mass and the ordinate is the brain mass, a straight line can be obtained through mathematical analysis, from which the expected value of the brain mass can be calculated from the body mass of the animal. The coordinates of some animals are exactly in this straight line, such as mice, dogs, horses, and elephants. Some animals have coordinates above this straight line, indicating that their brain mass is higher than expected and should be "smart". The farther the straight line is, the more brain mass exceeds the expected value, and the more "smart" it should be. This seems to be the case. For example, the mass of the human brain exceeds the expected value by 7.5 times, which is the highest of all animals and the most "intelligent". Dolphins are 5.3 times and monkeys are 4.8 times, both quite "smart". Conversely, if the coordinates of the animal are below this straight line, that is, their brain mass is lower than expected, it should be "dumb". The ratio of cattle is 0.5, which means that its brain mass is only half of the expected value, and it is indeed "stupid". However, there are exceptions to this rule. For example, the ratio of brain weight to "expected value" in South American capuchin monkeys is higher than that of chimpanzees, but far less "smart" than chimpanzees. For large animals, such as blue whales, the ratio of brain mass to expected values is also low (about 0.25), but blue whales are clearly "smarter" animals. Therefore, the relationship between brain quality and intelligence needs to be explored more deeply to find out better indicators. The number of neurons in the human cerebral cortex discusses the relationship between brain capacity and intelligence, can we look at the relationship between the number of neurons in the brain and intelligence? But not all neurons in the human brain are related to thinking. For example, the nerve centers responsible for some of the body's basic activities are mainly in the medulla oblongata. Vegetative people are completely unconscious, but these basic physiological activities continue as usual. So the neurons responsible for these activities can be considered unrelated to intelligence without consideration. The cerebellum accounts for about 10% of the total volume of the brain, and its neurons (mainly granulosa cells) are thought to be involved in the coordination of movement and can also be disregarded.
Overview diagram of brain neurons, source: Baidu Encyclopedia
The brain accounts for 82% of the total mass of the human brain, and the cerebral cortex (a few millimeters of tissue on the surface of the brain, which is the area where neurons in the brain are concentrated) is directly related to human thinking. The brains of other mammals also make up the majority of the brain volume, similar in structure and function to the human brain, so the number of neurons in the cerebral cortex may be a better indicator of animal intelligence.
Indeed, if we compare the number of neurons in the cerebral cortex in different animals, then humans are obviously the first, with about 12 billion nerve cells (different laboratories do not get exactly the same value, about 11 billion ~ 14 billion). Even if the brain of a whale is several times larger than the human brain, the number of neurons in its cerebral cortex is still less than that of humans, at 10 billion ~ 11 billion. The number of neurons in the cerebral cortex of cetaceans is similar to that of humans, but the intelligence is far inferior to that of humans. A sufficient number of neurons is a necessary condition for high intelligence, but it is not necessarily a sufficient condition.
The speed at which signals travel between neurons is important
The 12 billion neurons in the human brain do not produce intelligence on their own. When a baby is born, the neurons in the brain are fully formed, that is, they already have these 12 billion neurons. But newborn babies do not have obvious intelligence. It takes years for intelligence to develop from these neurons. Moreover, there is a critical period in the development of intelligence, which is closely related to the external environment.
The thought process involves different areas of the brain, and signals need to be transmitted and exchanged between neurons along the pathways between neurons (which we collectively refer to as nerve fibers). The smoother and faster the pathways that signals travel between different areas of the brain, the faster the brain can process information and the higher the intelligence is likely to be.
Overview of nerve fibers, source: Baidu Encyclopedia
Nerve fibers are slower to transmit signals. Different nerve fibers transmit signals at speeds ranging from 0.5 meters per second to about 100 meters per second. If we assume that the average is 10 meters per second, that is 1 millisecond for every 1 centimeter distance transmitted. At this transmission speed, the size of the brain has a great impact on the information transmission time.
For example, the brain of a cow is more than 200 times heavier than the brain of a mouse, with a diameter of 6~7 cm, which is much larger than that of a mouse of less than 1 cm. It also takes about 6 milliseconds for a signal to travel from one side of the cow's brain to the other. If thinking requires multiple back-and-forth exchanges of information between multiple parts of the brain, it takes longer for a cow to "think".
The shorter the signaling pathway, the higher the person's IQ
The human cerebral cortex is divided into many functional areas, and the thought process requires the exchange of information between multiple functional areas. Different people differ in the distance between the ribbons. In order to study whether the length of the distance between the functional areas of the signal is related to the intelligence of people, scientists used different methods to measure the distance between functional areas in different people's brains, and then compared these data with the intelligence of these people, and came up with similar results.
比如荷兰Utrecht大学医学院的Martijn van den Heuvel 等用功能磁共振(functional magnetic resonance imaging)来测定处于休息状态时人脑不同功能区之间的距离。 实验结果表明，有最短信号传输路径的人，智商最高。
Edward Bullmore, a neuroimaging expert at the University of Cambridge in the United Kingdom, used magnetoencephalography to estimate the speed of signal transmission between different areas of the brain, and compared it with the short-term memory of the test subjects, he found that the people with the most direct connections between the regions and the fastest signal transmission had the best short-term memory.
These findings support the idea that the distance between neural functional areas is directly related to the speed at which signals travel between them, as well as the level of intelligence.
Source: Baidu Encyclopedia
You may ask, aren't the brains about the same size and mass, and why are the functional areas so far apart?
This is because the shape of the cerebral cortex is different in different people. The surface of the human brain is not smooth, but full of sulcus. This allows the cerebral cortex to accommodate more neurons. Since the cerebral cortex is divided into many functional areas, different sulcus forms mean that the distance between functional areas is different between people, and the time it takes for signals to travel between these functional areas is also different.
For a particular person, if the distance between the two functional areas is shorter than the average distance, it is possible that the intelligence associated with the two functional areas will be higher. However, the distance between the other two functional areas may be longer than the average distance, and the intelligence associated with these functional areas may be poor. This may partly explain why different people have different talents.
Einstein's brain mass was only 1,230 grams, which is equivalent to 1,194 milliliters, which is significantly lower than the human average of 1,350 milliliters. But the parietal lobe of his brain has some peculiar ridge-like and groove-like structures. The small brain and special sulcus structure may have caused Einstein's neural pathways to think that were particularly short and unobstructed, thus forming his superhuman intelligence. However, he seems to be worse than the average person in terms of language, and he will not be able to speak until he is 3 years old.
Source: How Hard It Was for God to Create Man – The Key to Life
The picture comes from the Internet, and the copyright belongs to the original author
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