Extended brain growth
In humans, brain growth is limited by the width of the woman’s birth canal, through which the child must pass at birth. The selective advantage of an individual having a large brain reaches a natural limit here.
To overcome this natural limitation, evolution has found two solutions in human beings: The first solution is to prolong brain growth into the post-natal period. This solution is acquired by a further increase in effort because of the required and time-consuming care of the helpless infant.
Why, during the course of evolution, does the human brain simply stop growing? This question is just as fascinating as the question related to the causes of growth in previous periods. Surprisingly, it does not get discussed very much.
I had already quoted Ernst Mayr and I would like to repeat the quote here:
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)