The Valley of the Shadow of Doubt

What Science is .. and isn't. Part 2.
(C) 2007 -- all rights to revise reserved.

Out of the mists of Hollywood strides that champion of justice, the TV Prosecuting Attorney. As the suspense builds, the final hand is played : scientific evidence is presented that, beyond a shadow of a doubt, the accused is indeed guilty, because his fingerprints were found on the murder weapon.

The theory behind the use of fingerprints as evidence claims that fingerprints are unique; that no two people in the world have the same fingerprints. Has this ever been proven? No. While it is true that no two sets of fingerprints have ever been found to match identically, it is also true that not all the people in the world who have ever lived have been fingerprinted. It is therefore possible that somewhere in the world, at some time, two people have had identical prints. Since we do not actually know how many people there are and have been in existence, the probability of such identical prints can only be assumed to be zero. Thus it becomes a matter of faith that if the fingerprints on the murder weapon match the fingers of Suspect A, only Suspect A could have left them.

Even more reliable as evidence, supposedly, is DNA sampling. The theory states that no two people have identical DNA. Unfortunately, this cannot be proven, either. It may become possible, as the human genome is completely mapped, that the total number of human genes can be determined, and with that number present, an accurate probability of the uniqueness of each individual calculated. Nevertheless, until every set of human chromosomes, from every person who ever lived, is catalogued, it will not be possible to state with 100% certainty that no duplicate people exist of have existed in human history. Persons convicted on the basis of DNA sampling are convicted on the mere assumption that their DNA is unique to them.

While criminal courts tend to be somewhat conservative in regard to conviction on circumstantial evidence, civil courts are a different type of zoo. A criminal court jury is required to convict when all reasonable doubt of innocence has been dispelled; whereas civil court juries make their findings based on a preponderance of evidence. This preponderance of evidence often takes the form of high correlation; that is, if A is true at the same time B is true, A must have caused B. In its simplest form, this is easily seen to be ridiculous, but somehow, when faced with statistics, juries tend to react irrationally.

Thus it is, while there is a high correlation between smoking cigarettes and contracting lung cancer, it is also possible to contract lung cancer without smoking cigarettes, and it is also possible to smoke cigarettes for a long lifetime and never contract lung cancer. It is therefore impossible to prove that cigarette smoke (or even second-hand cigarette smoke) causes lung cancer, but that is scant comfort to cigarette manufacturers who have to pay out damage settlements awarded by scientifically impaired juries.

The same kind of "correlation is causation" thinking has cost many American businesses dearly. The Dow Corning breast implant case, the black lung, asbestos, and black mold cases, the scare over the use of the pesticide Alar, and even the now-reversed ban on the use of DDT, all involved fixing of blame based on correlations and the assumptions of causation.

A person may look at the statistics and decide that his probability of dying or getting a disease or suffering injury may increase with certain activities or the use of certain products. Based on that probability, he or she may decide that a lifestyle change is in order. That is a matter of personal responsibility. However, to punish a person or corporation (which is a non-human person) on the basis of the correlation of events is totally unjust. The Bible makes it clear that conviction must reside in the testimony of two or more witnesses, and if their testimony is merely an assumption that something has happened, it cannot be allowed.

It was noted in part one that many politicians are lawyers. Having been nurtured in the "correlation is causation" school of law, they bring their pseudo-scientific understandings to the realm of legislation. Thus we have bans on any substance or activity for which a proper scare can be ginned up in the voting public. It does not help that the media sensationalizes the most fantastic claims (follow the money, said Deepthroat) and provides free publicity for the most rabid of Snake-Oil Salesmen.

Where the situation becomes really pathetic is the teaching of quasi-scientific ideas in the science classroom. Evolution is an educational battleground, and the battle has been making a monkey out of just about everyone who gets involved. We will try to peel that banana next.