## Evidence and evolution (2)

Posted in Books, Statistics with tags , , , , , , , , , , , on April 9, 2010 by xi'an

“When dealing with natural things we will, then, never derive any explanations from the purpose which God or nature may have had in view when creating them and we shall entirely banish from our philosophy the search for final causes. For we should not be so arrogant as to suppose that we can share in God’s plans.” René Descartes, Les Principes de la Philosophie, Livre I, 28

I have now read the second chapter of the book Evidence and Evolution: The Logic Behind the Science by Elliott Sober. The very chapter which title is “Intelligent design”… As posted earlier, I was loath to get into this chapter for fear of being dragged into a nonsensical debate. In fact, the chapter is written from a purely philosophical/logical perspective, while I was looking for statistical arguments given the tenor of the first chapter (reviewing the differences between Bayesians, likelihoodists (sic!), and frequentists). There is therefore very little I can contribute to the debate, being no philosopher of science. I find the introduction of the chapter interesting in that it relates the creationism /”intelligent design” thesis to a long philosophical tradition (witness the above quote from Descartes) rather than to the current political debate about “teaching” creationism in US and UK schools. The disputation of older theses like Paley’s watch is however taking most of the chapter which is disappointing in my humble opinion. In a sense, Sober mostly states the obvious when arguing that when gods or other supernatural beings enter the picture, they can explain for any observed fact with the highest likelihood while being unable to predict any fact not yet observed. I would have prefered to see hard scientific facts and the use of statistical evidence, even of the AIC sort! The call to Popper’s testability does not bring further arguments because Sober also defends the thesis that even the theory of “intelligent” design is falsifiable… In Section 2.19 about model selection, the comparison between a single parameter model and a one million parameter model hints at Ockham’s razor, but Sober misses the point about a  major aspect of Bayesian analysis, which is that by the virtue of hyperpriors and hyperparameters, observations about one group of parameters also brings information about another group of parameters when those are related via a hyperprior (as in small area estimation). Given that the author never discusses the use of priors over the model parameters and uses instead pluggin estimates, he does not take advantage of the marginal posterior dependence between the different groups of parameters.

## Evidence and evolution

Posted in Books, Statistics with tags , , , , , , , on April 1, 2010 by xi'an

I have received the book Evidence and Evolution: The Logic Behind the Science by Elliott Sober to review. The book is written by a philosopher of science who has worked on the notion of evidence, in the statistical meaning of the word. I am currently reading the first chapter which is fairly well written and which presents a reasonable picture on the different perspectives (Bayesian, likelihood, frequentist) used for hypothesis testing and model choice. Akaike’s information criterion is a wee too much promoted but that’s the author’s choice after all. However I just came yesterday upon a section where Sober reproduces the error central to Templeton’s thesis and discussed on the Og a few days ago. He indeed states that “the simpler model cannot have the higher prior probability—a point that Popper (1959) emphasized.” And he insists further that there is no reason for thinking that

$P(\theta=0) > P(\theta>0)$

is true (page 84). (The measure-theoretic objections raised earlier obviously apply there as well.) It must thus be more of a common misconception among philosophers of science than I previously thought….

As described on the backcover, the purpose of the book is

“How should the concept of evidence be understood? And how does the concept of evidence apply to the controversy about creationism as well as to work in evolutionary biology about natural selection and common ancestry? In this rich and wide-ranging book, Elliott Sober investigates general questions about probability and evidence and shows how the answers he develops to those questions apply to the specifics of evolutionary biology. Drawing on a set of fascinating examples, he analyzes whether claims about intelligent design are untestable; whether they are discredited by the fact that many adaptations are imperfect; how evidence bears on whether present species trace back to common ancestors; how hypotheses about natural selection can be tested, and many other issues. His book will interest all readers who want to understand philosophical questions about evidence and evolution, as they arise both in Darwin’s work and in contemporary biological research.”

Sober applies these concepts of evidence to some versions of creationism… I am obviously reluctant to go through this second chapter about creationism as there is no use in arguing about the existence of gods in a book about science, but I am still curious to see how Sober analyses this issue.