This session address the role of chance in evolution. Lewens argues that selection is purely statistical, and that discussion of dynamics or forces is misplaced. Hong addresses the interplay of chance and reductive explanation in proposing "a gray scale of biological determinism."

Chair: Roberta Millstein

Tim Lewens*, Andre Ariew and Denis Walsh, University of Cambridge
"The Trials of Life"

Evolutionary theory is often characterised as a ėtheory of forces'. It is also sometimes described in statistical terms. But, it seems to us, that there is a deep tension between the dynamical and statistical conceptions of evolutionary theory. If one of them is correct the other is wrong. We distinguish the dynamical and statistical interpretations of selection and drift and argue that the dynamical interpretation is false. Evolutionary theory is an irreducibly statistical theory and not a dynamical one. Selection and drift are not forces acting on populations; they are statistical properties of an assemblage of ėtrial' events: births, deaths and reproduction.

Felix Hong, Wayne State University
"Towards a Gray Scale of Biological Determinism"

In 1936, Erwin Schr–dinger published a short essay "Indeterminism and Free Will" in Nature, and he dismissed free will as an illusion. Thus, despite the advent of quantum mechanics and the Uncertainty Principle, biological determinism is widely held among scientists. In the discussions among philosophers, the controversy between compatibilists and incompatibilists continues. On the physical side, physical determinism is also widely held presumably due to the continuing lack of consensus in the interpretation of quantum mechanics. At the heart of the problem is the apparent invariance to time-reversal of the equations of motion in both classical and quantum mechanics, which is enunciated as the principle of microscopic reversibility. More recently, Prigogine declared the end of certainty by forcefully proposing microscopic irreversibility with mixed responses from the physics community. For example, physicist Jean Bricmont dismissed Prigogine's view as illusion. This paper approaches the problem from both th------
First, we demonstrate, by a simple argument, that Laplace's famous proclamation "any belief that things come about randomly, or by chance, is simply due to our ignorance of the causes" can neither be proven nor disproven. This opens the possibility that there can be true endogenous noise. Second, the classical arguments in support of microscopic reversibility are re-examined in reference to the one-to-one-correspondence between the present condition (position and momentum) and any future or past conditions, stipulated in classical determinism. This one-to-one correspondence is entailed by the time-reversal invariance of the equations of motion. Again, by a simple argument, we demonstrate that microscopic reversibility is incompatible with macroscopic irreversibility despite the century-old belief to the contrary. Thus, it appears that microscopic reversibility is a good approximation but an approximation nevertheless. In support of Prigogine's claim but contrary to Bricmont's dismissal, it can be shown that------