A priori one would not expect humans to be near the physical limit of what's possible, purely based on the characteristics of the process that created us

Natural selection is

- random

- blind - gradient descent is prone to getting stuck in local minima, has no foresight, no ability to go back to the drawing board, no "understanding" of what it's doing.

- not even optimizing for intelligence, except instrumentally - to the extent that increasing intelligence interferes with survival, it has to be sacrificed

- subject to hard constraints like the limits on size imposed by childbirth