Anatomy is not destiny, but it is not irrelevant either. — Carl Sagan

A mutation in a DNA molecule within a chromosome of a skin cell in my index finger has no influence on heredity. Fingers are not involved, at least directly, in the propagation of the species.

There is a popular contention that half or more of the brain is unused. From an evolutionary point of view this would be quite extraordinary: why should it have evolved if it had no function? But actually the statement is made on very little evidence.

Absence of evidence is not evidence of absence.