This claim exemplifies the naturalistic fallacy by arguing that the way
things are implies how they ought to be. It is like saying that if
someone's arm is broken, it should stay broken. But "is" does not
imply "ought." Evolution is descriptive. It tells how things are, not
how they should be.
Humans, being social, improve their fitness through cooperation with
other people. Even if survival of the fittest were taken as a basis
for morals, it would imply treating other people well.
