Explanation:

Perhaps equally remarkable is the fact that since Homo sapiens reached this stage more than 100,000 years ago, there has been no further significant increase in brain size.

It is difficult to understand why natural selection gave primitive humans such a perfect brain that 100,000 years later it would enable the achievements of a Descartes, Darwin or Kant or the invention of the computer, trips to the moon or the literary creations of a Shakespeare or Goethe.
(Mayr 2002, p. 501)

Above, I posed the question as to whether Ernst Mayr is right with the statement of the perfect brain of Homo sapiens. Now here is the answer: Yes and no. He is right, because the human brain has found a miracle cure, so to speak, with its networking capabilities that enable it to access unlimited brain capacity via the network.

But Mayr would not have been right if his contention that the brains of Descartes, Darwin or Kant alone would have done their great work without the help of the human network of clever forerunners, critical contemporaries, interested discussion partners, etc. had been understood in such a way.

The end of hominid brain growth is a paleoanthropologically verifiable fact that is associated with the appearance of modern Homo sapiens.