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Author Topic: Phylogenies in the Courtroom  (Read 862 times)

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Offline DarklingAliceTopic starter

Phylogenies in the Courtroom
« on: November 20, 2010, 11:11:10 PM »
It is a rare case when court cases get to invoke DNA (EDIT: or in this case, I suppose RNA) evidence and high-tech lab work. Most of that is relegated to the realm of fantasy, rather than actual criminal justice. But when it does happen...it is really, really awesome. I can think of few more heinous crimes than that of Anthony Eugene Whitfield, and I am so happy that science was able to provide supporting evidence to put him behind bars.

Quote
To demonstrate Whitfield’s guilt, the prosecution had to show that he had wilfully exposed women to HIV, that his five HIV-positive partners contracted their infections from him. Fortunately, David Hillis from the University of Texas and Michael Metzker from Baylor College of Medicine knew exactly how to do that. They had evolutionary biology on their side.

Hillis and Metzker knew that HIV is a hotbed of evolution. The bodies of HIV carriers produce around a billion new virus particles every day, and their genomes change and shuffle at furious speeds. But when infections pass from one person to another, this viral variety plummets. Thousands of genetically distinct viruses might jump into a new host, but usually, only one of these managed to gain a foothold and set up a new infection. Every time it moves from host to host, HIV passes through a genetic bottleneck and that provides a massive clue about who passed an infection to whom.

Armed with this knowledge, Hillis and Metzker analysed HIV genes from six anonymised blood samples – one from Whitfield and five from the women he allegedly infected. They had no way of knowing which was which. The genes revealed that the viruses were all closely related to each other, and more so than to viruses from other HIV-positive people in the local area.

Using these sequences, Hillis and Metzker constructed a family tree for the viral genes (a ‘phylogeny’), to show their evolutionary relationships and, more importantly, to work out which sequences came first. The tree was damning – one group of viruses was clearly the ancestor of at least four of the others, and probably the fifth. The owner of these viruses, known only as ‘WA04cd’, must have been the source of the related infections. Once the study was complete, the prosecution revealed that the identity of this mystery carrier was none other than Anthony Eugene Whitfield. Once the defense saw the evidence, Whitfield admitted to being the source of the infections.
http://blogs.discovermagazine.com/notrocketscience/2010/11/15/evolutionary-trees-help-to-convict-men-who-knowingly-infected-women-with-hiv/
« Last Edit: November 20, 2010, 11:57:05 PM by DarklingAlice »

Offline Oniya

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Re: Phylogenies in the Courtroom
« Reply #1 on: November 20, 2010, 11:35:38 PM »
I used to work IT support in an HIV research lab.  I got to see some of the DNA sequencing (not that particular case, though - it's been over 9 years ago.)

But actually, DNA evidence is getting far more common, especially through the efforts of groups like The Innocence Project, and as a consequence of the 'CSI Effect'  (Jurors virtually expect the high-tech forensics, after having seen them in popular dramatic series.)
« Last Edit: November 20, 2010, 11:37:14 PM by Oniya »

Offline mystictiger

Re: Phylogenies in the Courtroom
« Reply #2 on: November 21, 2010, 09:41:12 AM »
Quote
It is a rare case when court cases get to invoke DNA (EDIT: or in this case, I suppose RNA) evidence and high-tech lab work

Except for most sexual assaults, paternity issues, identification matters, or medical negligence...

Offline DarklingAliceTopic starter

Re: Phylogenies in the Courtroom
« Reply #3 on: November 21, 2010, 12:39:23 PM »
But actually, DNA evidence is getting far more common, especially through the efforts of groups like The Innocence Project, and as a consequence of the 'CSI Effect'  (Jurors virtually expect the high-tech forensics, after having seen them in popular dramatic series.)

This is true. Although (unfortunately) the Innocence Project moves fairly slowly, and could really use more manpower and funding. However, that DNA analysis (for all that it is 'high-tech') usually amounts to little more than fairly shallow 'genetic fingerprinting'. What we are dealing with in this case is more complex.

It isn't enough to merely demonstrate that Whitfield had slept with these women. That was taken as granted. What had to be shown was that: of the 17 women he had slept with, the 5 that become HIV positive had become HIV positive through infection by Whitfield specifically. Which is a fair bit more impressive than matching a hair found at a crime scene to a specific blood sample.

Offline Oniya

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Re: Phylogenies in the Courtroom
« Reply #4 on: November 21, 2010, 01:07:35 PM »
Far more impressive, I agree.  As I pointed out, I've seen the sequences and parts of the 'family tree' of the HIV virus.  Unfortunately, the same hyperactive evolution that makes identification like this possible is the same thing that makes finding the cure so difficult.

Offline DarklingAliceTopic starter

Re: Phylogenies in the Courtroom
« Reply #5 on: November 21, 2010, 01:24:57 PM »
No kidding. The virus strain you are infected with initially can have a 5-10% (at a conservative estimate) variation in structure over the ~10-12 years that it takes to progress to AIDS. It's one of the reasons that I lament ever finding a traditional vaccination method, although alternatives (such as CCR5 manipulation) are showing some real promise these days.

Offline mystictiger

Re: Phylogenies in the Courtroom
« Reply #6 on: November 22, 2010, 05:56:22 PM »
From a purely legal perspective, there are rarely 'exciting' biological things that can determine a case one way or the other. This is rather a factor of the rules of evidence in most jurisdiction - there has to be corroboration. To find someone guilty you need to establish the actus reus, the mens rea, and the absence of a defence in as many different ways as possible. It is 'just another' piece of evidence. I'm reluctant to comment on the specific case without having read the case-report, but from a purely legal stand-point, there would be plenty of other evidence. Without establishing that the accused had actually had sex with these women, it would be a possible defence that they contracted it from another source. You'd need to prove this beyond reasonable doubt, meaning that the defence would probably have their own genetic experts to show that this is the most common strain in a given locality. And so on.

One thing that I was working on relatively recently is an example of high-tech genetics being absolutely crucial. We were presented with a man who died of anthrax. This is ... somewhat uncommon. The knee-jerk reaction of the security services was that this was some kind of bioterrorist attack gone wrong! Especially when we found out that the strain of anthrax was a West African one (e.g. not one native to Scotland, therefore one that could have been contracted in the 'normal' fashion). We then dug deeper and could find no links with any terrorist organisation or plot or extremists of any kind. It turns out that our chap had contracted anthrax from an untreated drum-skin. It was therefore a perfectly possible explanation for how we found African anthrax in a small, quiet suburb without any foul play. It was just a one-in-a-million chance kind of thing. Poor chap - he was severely immuno-compromised and what offed him was the drum he played in his support-group meeting.

It is easy to say that the courts rarely get to play with the high-tech toys. The truth is that it all depends on how much money the parties are willing to throw at a given court-case. I've seen CERN physicists advising on radiation matters, leading geneticists on matters of identification, nobel-prize winning physicians on medical causation, and so on.

I would expect that as genetic technologies become cheaper and easier, biotech evidence will become far more common. We can step beyond the often risky science of fingerprint evidence and the always-biased recollection of expert witnesses. Such a development is always to be welcomed - House got it right when he said that people lie. They don't necessarily do it deliberately, but it is rarely the case that a witness doesn't screw something up. This is absolutely to be welcomed in terms of sexual assault. There are few things crueler than the way the legal system currently expects victim-witnesses to confront their accusers. Ideally, we wouldn't have to call them. We have semen samples, we have evidence of bruising, tearing, elevated cortisol levels, and so on. This way we don't have to sacrifice the poor victim's sanity and self-respect in order to nail the attacker.

In this regard, I think the whole CSI-myth is unhelpful. There's a great deal we can do with biotech evidence, but it is a long way in the future that it is all that we can rely on. At the same time, the Court doesn't really cover itself in glory (at least in this country) in the way that they respond to expert evidence - the British courts have explicitly rejected Baysian probability. I'm kind of glad that they have because I've not understood it on the several times it's been explained to me.