In his new book, Kluge: The haphazard construction of the human mind, Gary Marcus describes the brain as a clumsy collection of spare parts.

Evolution tends not to optimise things; it simply tinkers with what’s already there, he says. So it tends to make things better but there’s no guarantee that it will make the best.

“Survival of the fittest” really means
fittest of the available options. Evolution can’t take a step back and ask what the best option would be; it just works with what it has. And that’s what leads to tinkering and ultimately the kluges.