No, this post is not about hangovers. It’s about evidence. Ideas as to what is evidence have varied, somewhat, over time. (SPOILER ALERT)
For instance, “Murder comes to Pemberley” by P. D. James, features a trial scene. Mr. Wickham, a character from Jane Austen’s “Pride & Prejudice” is on trial for murder. The implied date of the trial is approximately 1804. The UK lacked a police force at that time. The local magistrate has performed the police function and he has made the decision to charge Mr. Wickham with the murder of Lieutenant Denny.
The trial is in the local assizes court and the magistrate and his witnesses constitute the evidence against Mr. Wickham.
There are certain known and agreed facts. Lieutenant Denny is dead and he died from a head injury. In fact he had more than one head injury. He was last seen entering a wood, followed by Mr. Wickham. Mr. Wickham was located in the wood with the body, having dragged it some distance from where he found it, he said, with the injuries. He also claimed to have seen somebody fleetingly in the wood and he fired Denny’s pistol at that person but missed.
As always, the prosecutor is an experienced barrister. Luckily for Mr. Wickham, Mr. D’Arcy has arranged legal representation, by a barrister, for Mr. Wickham. That was an unusual element of Mr. Wickham’s trial. Only about twenty years before Mr. Wickham’s trial did criminal trials begin to feature defence lawyers. (They were barristers; solicitors had not come into being).
Unluckily for Mr. Wickham, the judge is from the old school; he sees little role for the defence barrister and prevents him from trying to restrain the prosecutor. The prosecutor introduces evidence of Mr. Wickham’s persistent failures to pay his tradesmen’s bills. “Evidence” like that is in fact the prosecutor’s case against Mr. Wickham. Mr. Wickham is not a likeable person and is generally not liked.
Mr. Wickham, apparently, gives evidence himself of what happened. His evidence goes down like a lead balloon. There are two reasons for this.
Firstly, he should not have been allowed to give evidence. The then law of evidence would have deemed him incompetent to give evidence because of interest. It was only in 1898 that this rule was changed for criminal defendants. For civil cases, it was changed in 1851. It was presumed that a defendant could not be expected or trusted to give reliable evidence when so much was at stake for him in the trial. Therefore he was, or should have been, precluded from doing so.
Secondly, his evidence was not the explanation that everybody wanted. How had Lieutenant Denny died? In fact, in offering his evidence, Mr. Wickham was, in an unexpressed manner, conceding that he had to prove something about the death of Lieutenant Denny and that that had to be exculpatory of him.
He failed in his proofs and failed to exculpate himself. Consequently, he was convicted. (That’s all, about “Murder comes to Pemberley”, in case you have not yet read the book or seen the TV series.)
What, in modern times, is good evidence?
The answer, as in 1804, is that it depends on the audience.
Here is my current favourite item of evidence.. We suffer from two small pests. They are head lice and pubic lice. The lice are exclusive to humans. The head lice have cousins; those cousins are found living on chimpanzees. The pubic lice have cousins also; they are found living on gorillas. Analysis of the genetic differences between the lice shows that our head lice diverged from the chimpanzee lice five million years ago. Our pubic lice diverged from the gorilla lice about 3.3 million years ago.
The divergence date of five million years from chimpanzee lice is significant and consistent with the estimated date of divergence of humans and chimpanzees.
The divergence date of 3.3 million years from gorilla lice is not consistent with the estimated date of divergence of humans and gorillas.
Put succinctly, one piece of evidence supports the contention that humans and chimpanzees had a common ancestor; the other piece of evidence supports the idea that early humans and gorillas were in close contact
It is not evidence that gorillas gave their lice to humans (or that humans gave their lice to gorillas).