The history of organic life is undemonstrable; we cannot prove a whole lot in evolutionary biology, and our findings will always be hypothesis.
Jeffrey H. Schwartz, Professor of Biological Anthropology, University of Pittsburgh, February 9, 2007
we must concede that there are presently no detailed Darwinian accounts of the evolution of any biochemical system, only a variety of wishful speculations.
Prof. Franklin Harold, "The Way of the Cell", Oxford University Press, 2001