In the evolution of mankind, humans had to survive very tough environments for hundreds of thousands of years.
It can be safely stated that most modern humans would not have a chance of surviving in the prehistoric times. The human brain evolved to survive in this harsh environment. The size of the brain was apparently considerably larger in the human species 300,000 years ago.
Of late, there are plenty of things being automated with computers and robots. As life starts to get easier, some of the functions of the brain like having skills to survive in a harsh environment go away.
It would be interesting to note how the human brain would look in a few hundred years from today.