In John Stuart Mill's influential transmittal of the Positivist doctrines of August Comte to the world of science in 1865 he wrote of humankind progressing: " the positive" [era] ", which is destined finally to prevail, by the universal recognition that all phaenomena without exception are governed by invariable laws, with which no volitions, either natural or supernatural, interfere."

Positivist science's insistence on denying human volition a place in the procedures of science led first to the exclusion of volition from scientific discourse, as a result to an absence of findings confirming the existence of a self able to exercise volition, and finally to the assertion that the absence of such evidence proved volition couldn't exist.

Fast forward to the present day and the dominant philosophy in the "Schools" is Physicalism -- consciousness may exist but it cannot be a source of volition, only physical agents can affect other physical agents, only brain chemistry could direct behavior. Our sense of consciousness being the source of volition, capable of directing our behavior, is an illusion.

Charles Darwin became a very early convert to Positivism just as he was trying to come up with a mechanism for evolution. Not surprisingly the process he came up with involved no aspect of the self or consciousness. Near universal acceptance of that theory nicely confirmed the doctrine of Physicalism.

Today it's pretty obvious that the conscious self can be an agent in evolution. If you don't accept that our exercise of conscious volition has affected our own evolution, look at how we're affecting the evolution, in term of differential survival, of the Earth's other living creatures.

If the humanities were to deny volition, wouldn't that mean shutting up shop entirely? If instead you turn around and insist the conscious self can exercise volition, then you have to include in your theories of evolution some means by which conscious volition could have evolved. That eliminates purely physical mechanisms such as natural selection.

That's raises the question: if by scientific we mean accounting for conscious volition while remaining true to Positivist doctrine, can there be a scientific theory of evolution?

What about Charles Darwin's theory of natural selection, as updated by the addition to it of random mutation, doesn't that count as a scientific theory? James Shapiro's "Evolution: The View from the 21st Century" suggests not--see the review in this site's forum.

That removes any logical barrier to supposing that the process of evolution itself may involve a capability for volition.