The human brain has been shrinking since 70,000 years ago

Humans have acquired the ability to use fire, walked upright, and developed an elaborate language. By building a more sophisticated civilization and having a complex brain, we are now able to plan the future and process the past. Of course, these were made possible by the evolution of the brain, but in fact, it is known that the volume of the human brain has been shrinking since about 70,000 years ago. The University of San Francisco presents an essay by student Savannah Robison in 2017 summarizing the tendency of brain shrinkage and its causes.

“Why Are Our Brains Shrinking?” | The Science of Life
https://usfblogs.usfca.edu/biol100/2018/03/20/why-are-our-brains-shrinking/

John Hawkes who is the anthropologist of the University of Wisconsin, the human brain in this 20,000 years has claimed to have reduced from 1500cm ³ to 1350cm ^3. Furthermore, it is known that the gray matter, which controls complex behaviors and abilities peculiar to humans, such as language, culture, and letters, is reduced, not the white matter , which is a mass of nerve fibers.

Various theories have been put forward as to why the volume of the brain is decreasing. For example, there is a theory that 'because the brain and body correspond'. This is because the size of the body and the size of the brain are linked from the idea that 'the more muscles there are in the body, the more the brain is needed to control those muscles', and it is in the process of evolution. It is thought that the human body gradually shrank and at the same time the brain became smaller.

Also, the larger the brain, the more fuel it needs and the longer it takes to develop, but as a result of the evolution to 'get the most intelligence with the least energy', the nerves of the brain wire more efficiently. There is also the idea that the volume of the brain has decreased. In addition, from birth to the mid-20s , humans perform synaptic pruning that removes unnecessary synaptic connections and strengthens only the necessary synaptic connections, but the amount of information handled by humans increases and the language becomes complicated. It is also argued that this synaptic pruning progressed and the brain became smaller.

In addition, there is a theory that 'humans have reduced their brain volume because they have been domesticated.' When dogs and horses are domesticated by humans, it is said that their brains are 10 to 15% smaller than their wild ancestors, based on the idea that 'humans are domesticated monkeys.' I am. However, 'domestication' here does not mean that humans have been domesticated by something, but that humans have become social animals that can discuss and understand disagreements rather than killing each other. To do.

'As the Earth's cold and warm seasons have ended, the body has become smaller and at the same time the skull and brain have shrunk in order to improve heat release efficiency and adapt to warmer climates.' Various theories have been considered, such as 'because a woman's pelvis has shrunk, her skull has shrunk, and her brain volume has shrunk.' 'Simply because humans have become lazy and their intelligence has declined.' increase.

Finally, Robison said, 'Modern human brains may have become smaller, but we have more information than ever before. Depending on how we use this information, we can prosper. You can walk or you can go on the path of hardship. Whether our brains will be our greatest benefit or our most unfavorable asset, it will solve our time. ' Stated.