Re: Can we be 100% sure that DNA is the transforming principle

Speaking today, I can say we are 100% sure that DNA is the transforming 
principle. But, but, but, this does not follow suit with all of science 
and should not be a basis of comparison.

Scientifically I would say that there is never a 100% assurance that any 
ONE experiment explains the nature of a compound.  In fact, the 
experiments you mentioned did not convince everyone at the time. When 
Griffith did his transformation experiments, although convincing now, 
people were extremely skeptical. The main argument was that DNA was just 
too simple to be responsible for heredity. Four compounds only; A,T,C and 
G. Proteins had 20. Therefore the variability was tremendously different 
between the two macromolecules. It just seemed more reasonable to assume 
that such a complex process needed a complex molecule.  

When Avery and others digested DNA and protein and found that only the 
undigested DNA was able to be inherited, there were still critics. The 
difference now was cooroboration in the argument of DNA as the heritable 
factor.  More than 1 person using different experimental techniques 
concluded the same thing. 12 years later Hershey and Chase came to the 
same conclusion, but once again with a different method. Separately, they 
only suggested a hypotheis but together they strengthened the argument.

The work to show that DNA was the heritable factor was sought out for 
years, with many scientists.  And although not published, I'm sure there 
was just as much work to prove that proteins held the heritable factor 
(although not very convincing).  The collected work became one piece of 
the puzzle. Knowing what we know now I think we can now say with 100% 
certainity that DNA is the heritable factor.  But there was no one 
experiment that would show it. Nowadays, to find an experiment to prove 
it with one try, I believe, misses the point. Allow me to explain futher.

To answer your question of whether there is an experiment designed that 
will 100% prove a case. My answer is no.  But I believe that is the 
beauty of science.  I personally do not believe there is any experiment 
for any question that will 100% prove or disprove a hypothesis. Just as 
for the discovery of DNA as the heritable factor, so too will future 
discoveries require a number of skeptics and believers to find the 
answers needed. Only then will we one day be able to say with 100% 
certainty how something works.

I also want to address your argument about the potential of being 
contaminants from the biological source.  This is very true, but this 
sort of argument, I believe, can lead us down a dark path.  This also is 
why a number of experiments, performed independently, and under different 
circumstances is required to show with reasonable certainty that a 
hypothesis is correct. Even though the classic experiments set forth by 
Griffith, Avery, Crick and others are works of genius to our standards, 
it is understandable to see why the critics existed. Critics to this day 
still exist; maybe not for the purpose of arguing a proteins sole role in 
heredity, but certainly for other areas of science.  For instance, some 
scientists do not believe that the HIV virus is responsible for AIDS.

To argue for contamination is a fine line. In one experiment, it is 
reasonable. But when the evidence is overwhelming I believe this line of 
reasoning calls into question every experiment published to date. 

I think that as long as there are good controls one can only state the 
conclusions that the experimental results suggests. In time, more 
experiments will yield more results, either strengthening or weakening 
the initial argument. With enough time and with the general consensus of 
the scientific community it will become reasonable to say, "Yes, we are 
100% certain of this process."  This is science and because of our 
limitations at the time of the experiment (whether it be 1942 or 2042) we 
will always need to seek additional evidence in support.

However, I do not believe that one experiment will ever let us say 
anything with 100% certainty. 

Lastly, I think that if we, in hindsight, were to try and create an 
experiment to 100% prove that DNA is the heritable factor, we would have 
to assume what is known from the past is also 100% true. Our experiments 
must be based off of previous knowledge. Therefore our results are only 
as true as the background information we established our experiment 
around. Logically speaking, this would make it impossible to design a 
fool proof experiment.  If contamination was the result of us concluding 
DNA was the heritable factor, then what is to stop us from arguing that 
any tecnique we use to test this is also not contaminated and therefore 
affecting our "fool-proof" experiment?

Rather, we should demand a series of evidences for any process that 
occurs in the cell before we are 100% certain about what is going on. 
This in essence is hypothesis driven research and I can't see a better 
way of doing it.

Although I didn't give you the simple answer, and at times detracted from 
your initial question, I do hope my response makes sense and keeps you 
thinking about the bigger issues we face today.