The Neanderthal and Cro-Magnon lived in the same natural landscape together for 50-24 thousand years. The Neanderthals died out, but the Sapiens remained.
In ancient man, the size of the brain was 1600-1800 cm3. The average volume of a modern person is 1400 cm3. And as a result, 250 cm3 was lost in 25 thousand years, which is very significant. This is explained by the social nature of modern man, and by the fact that society takes on a lot of the functions that the individual performed in the past.
But such reasoning cannot be recognized as obvious. First, social relations have always existed at all stages of human evolution, therefore, they should have been structurally realized in the development of the brain even at the stage of lower apes. Secondly, social relations only became more complicated, and, therefore, the brain, which supposedly serves them, should become more complicated. Thirdly, maybe such a decrease in brain size indicates a banal degradation of some brain structures developed in our venerable ancestors, due to the uselessness of a modern person?
I will try to describe a hypothesis explaining the evolution of our brains. Let's start with that ancient man who did not yet know how to use various devices, but only started to master them. Each of us goes through this difficult period of our life from 1 to 4 years. At this moment, the size of the brain, referred to the size of the body, is the largest. In the process of development, skills are acquired to use a variety of objects, and gradually the ratio of the sizes of the brain and body changes towards the body. We think this is natural, since everything happens during the growth of the body.
The ancient man, who did not possess adaptations (obsidian knife, spearheads, arrows, etc.), had to replace the absence of these things with the complexity of his behavior, but at the same time have the potential for the development of technology. Consequently, his brain was more loaded with information about the world around him. Moreover, all the information was vital.
Further development was accompanied by the invention of more advanced tools and weapons (spears and arrowheads for them), the use of fire for making tools and cooking has led to the degradation of the part of the brain responsible for fighting predators with bare hands, night vigil, finding food that can be consumed without the use of fire.
The flexible structure of the evolving Cro-Magnon brain made it possible to replace the lost structures with new ones responsible for associations. The development went in the direction of the development of creative abilities, but in terms of volume, less costs are needed for them than for the struggle with the objective circumstances of life in the absence of tools and weapons. Consequently, during replacement, there was a reduction in the volume of incoming information and in the size of the brain.
Each new invention replaced some function of the brain, and led to the degradation of some departments and the development of others. The information coming from the outside world lost its vital importance, and acquired social importance. The invention of javelin throwing saved mankind from the need to get close to the animal when hunting, which reduced the brain, for example, by 10 cm3, and the invention of the bow by another 10 cm3.
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Since the inventions influenced the brain in a complex manner in many ways at the same time, the overall effect was so significant (250 cm3). If we assume that the degradation of the brain is associated with the stages of inventions that took on part of the functions compensated for by previously complex human behavior, then modern computerization replaces the computational abilities of a person and, in a complex, many other functions. Following the logic of the substitution hypothesis, 2-3 generations will pass and a person will lose another 200 g of brain and approach Homo erectus, from which he originated. I wish you success!
The thesis is any appearance of a new instrument for business +, for brains -. Laziness may have made us human, but it hasn't made us smarter.