The Importance of Evidence in Science

My school Chemistry text book told me that atoms are like the solar system: in which electrons orbited the central nucleus just like the planets in our own solar system orbit the sun. The truth is much more complex, and the recent announcement that the Higgs Boson (a particle that confers mass on other subatomic particles) has been "seen" using a high energy particle accelerator doesn't really fit with the simple model that I used to get me through my chemistry exams. But that's OK because it was an early stage in my journey to making discoveries of my own (or more accurately with colleagues) and I developed a level of understanding that enabled (or empowered) me to question established facts and concepts and to make up my own mind. This can only be achieved by looking at the "evidence" that has been used to justify a particular conclusion. So what is evidence and how do we evaluate it?

The Oxford English Dictionary defines "evidence" as follows:

                "The available body of facts or information indicating 
                 whether a belief or proposition is true or valid"

There is a problem with this definition, since a fact can be challenged by an experiment, which often happens as new technology emerges. So, until about 1985, we believed that all enzymes were proteins. Tom Cech and Sidney Altman, independently demonstrated that RNA, previously thought to be an information molecule, could also catalyse certain biological reactions. Not only has this subsequently been confirmed by many labs, but it has opened the way for a new way of thinking about genes and gene therapy. 

In this case the facts changed and therefore new evidence was used to displace the protein-centric idea. Facts in Science only remain set in stone after they are subjected to rigorous investigation. The double helix of DNA, now an iconic symbol, was thought to comprise 3 strands, until Watson and Crick (not forgetting of course Rosalind Franklin and Maurice Wilkins) demonstrated unequivocally, that it was a double helix...until of course we discovered Z DNA and quadruplexes at the tips of our chromosomes. But don't panic, double helical DNA is here to stay, it is just that when solid evidence is presented that challenges the universality of this structure it often explains things that were a little awkward to accommodate, in this case recombination and chromosome crossing over.

Geoff Schatz

So how do we deal with the "moving target"  or "shifting sand" that is the scientific evidence base? My first suggestion is to embrace it: always challenge a concept or fact by asking yourself this question. What is the definitive (or most compelling) experimental result that led to the formulation of a hypothesis? When Geoff Schatz was head of Biochemistry in the Biozentrum at Basel (Switzerland) he transplanted short segments of amino acids that he suggested were responsible for targeting proteins to the mitochondria (the organelle that generates cellular energy) onto cytoplasmic proteins. The result was that these proteins were now targeted to the mitochondria. This is referred to by Molecular Biologists as "an elegant" experiment: it cut to the heart of the problem and yet is very simple in concept. Of course Schatz was drawing on on years of experience, great insight, formidable technical skills and of course he was a bit of a genius! This concept remains robust, but there are exceptions: the important thing is that Schatz's (and others similar scientists) provided us with a model that allowed us to move forward in the lab in a logical and constructive manner. If the Schatz rules need to be overturned or modified by new and perhaps more compelling evidence, then so be it. This is how we progress in Science. Next, think about who judges the quality and significance of the evidence?