The whole point of “fitness,” in an evolutionary context, is reproduction. One has higher “fitness” if one can have more offspring.
The problem with science, as Del Ratzsch has pointed out, is that it is done by people.
We can only say that so it is.
If one insists on and is committed to naturalism, then naturalistic, evolutionary, explanations are what you will find.
Theodosius Dobzhansky famously wrote in 1973 that “Nothing in Biology Makes Sense Except in the Light of Evolution.”
There is much to agree with in Yale University clinical neurologist Steven Novella’s recent article on the p-value.
It is an enormous problem to explain how such capabilities evolved.
According to evolution, the species arose as a consequence of random events, such as mutations.
The degree of regulation and control required for this system is not only enormous, but contrary to evolutionary expectations.
There are conflicting evidences, a lack of details, opposing hypotheses held with great confidence, and a wide range of explanatory mechanisms that are routinely used as needed.