Jacques Barzun wrote clearly in his book, Darwin - Marx - Wagner - A Critique of Heritage, how the concept of biological evolution became melded to the concept of natural selection during the 19th Century. The conflict between evolution on the one hand, and evolution solely by the mechanism of natural selection on the other was clear during a time when philosophical depths were more widely plumbed. The ethical implications for the idea that man is nothing more than a biological machine created by mindless forces is abominable and thus the conflict keeps returning. Writes Barzun:

"...the error which dogs evolutionists, the error of believing that if you isolate the elements or label the beginnings of a process you have thereby grasped the process in its entirety. Because living things depend on certain chemico-physical things, therefore human beings are physico-chemical combinations and nothing more. This error is the so-called "genetic fallacy"...It is a common error and the very one, incidentally that both sides fell into when disputing over the origin of species...

Both should have known that becoming or growing, if is means anything, must mean a change not reducible to the stage before, much less to the original stage of the process. Something exists at the end which was not there at the beginning. An oak may come from an acorn, but it is not identical with an acorn, nor even with an acorn plus all that the oak has absorbed of moisture and food in the process of growing upwards. This problem of Becoming was the staple of discussion for the whole half century of Romantic thought before Darwin and Spencer. To the Germans particularly - Hegel, Schopenhauer, Schelling and Fichte - we owe the establishment of the basic evolutionary notion that Being is Becoming and that fixity is an abstraction or an illusion. Unfortunately, this view was linked in biology with the principle of vitalism, or life force, which though it inspired very fruitful researches into the nature of living cells, ultimately proved untenable. The difficulty is that if there is no superadded life force in living beings, seemingly nothing but matter is left. Remove the mysterious, "metaphysical" soul or controlling power and mere physical an chemical units remain behind. From these everything else must now be explained in "positive" terms."

In other words, the living cell differs from the dead cell in some fundamental qualitative way and the living cell cannot be reduced to its component parts without killing it - removing its metaphysical component. By removing the metaphysical component of philosophy, we likewise kill it, by destroying the source of its vitality.