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Air is full of DNA

nature.com

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Re: Air is full of DNA

#51

Post by NoMoreNicksLeft »

chiph wrote: post #35
ch4s3 wrote: post #34

Earlier quoted context omitted.

But we’re they at the scene or did they just bump into someone or something that was there?

That's something that would have to be addressed at the trial by the defense attorney raising challenges. If the DNA is present, it's present - barring any procedural mistakes by the forensics technicians (mislabeled sample, dirty lab equipment, didn't follow manufacturers instructions, etc). Or deceit by one or more members of the forensics team to implicate the suspect.

>That's something that would have to be addressed at the trial by the defense attorney raising challenges.

This is the wrong point at which to correct the problem. When prosecutors are allowed to introduce "science" as their evidence, jurors give this way too much deference. It's the prosecutor basically saying "you're too stupid to understand it, so indulge my appeal to authority" and jurors tend to happily acquiesce. This is why judges are supposed to gatekeep expert testimony and not just let any quack step in and make outrageous claims... and despite their attempts, quacks have repeatedly done just that these past few decades.

If is true that the presence of DNA means essentially nothing, then it shouldn't be permitted to be introduced at trial. Protection from wrongful conviction shouldn't rest on someone having an attorney expensive enough to be able to unsway too-easily-swayed jurors with counter-specious arguments.

Re: Air is full of DNA

#52

Post by russdill »

dkobia wrote: post #24

This always blows my mind. We are currently breathing in the DNA of the trees, animals, and people around us—and we’re leaving ours behind for them, too. We’re all one big genetic soup.

The world of the very small is a very strange place https://en.wikipedia.org/wiki/Disappearing_polymorph

We can't make a certain HIV drug anymore because after 2 years, a lower energy crystal state formed, and that state isn't as effective. Now anytime we try to form synthesize the drug it finds a molecule of the lower energy crystal state which causes the crystal to also form in the lower energy state.

Re: Air is full of DNA

#53

Post by pfdietz »

throwaway27448 wrote: post #48
pfdietz wrote: post #27

Earlier quoted context omitted.

> birds are dinosaurs Not that I doubt that, but how does DNA help, when we have no DNA samples from dinosaurs?

Birds are dinosaurs because they are in the clade dinosauria. Their closest living quadrupedal relatives by genetic distance are indeed crocodiles. But you're right, it is the fossil record that provides the strongest evidence.

I meant, "we have no DNA evidence from non-avian dinosaurs".

Saying that birds have the same DNA as birds is not evidence of much of anything. :)

Re: Air is full of DNA

#54

Post by throwaway27448 »

pfdietz wrote: post #53
throwaway27448 wrote: post #48

Earlier quoted context omitted.

Birds are dinosaurs because they are in the clade dinosauria. Their closest living quadrupedal relatives by genetic distance are indeed crocodiles. But you're right, it is the fossil record that provides the strongest evidence.

I meant, "we have no DNA evidence from non-avian dinosaurs". Saying that birds have the same DNA as birds is not evidence of much of anything. :)

I think the genetic distance from crocodiles is still pretty strong evidence.

Re: Air is full of DNA

#55

Post by ksaj »

azalemeth wrote: post #19

I do often wonder about stories like this in the context of forensic science – my (incomplete!) understanding a lot of the time suspect DNA samples are taken from small areas and amplified significantly with high-cycle count PCR. I'd worry that any jury presented with a statistical argument about a fragment of somebody's DNA being very unlikely ("1 in 100 million") to be different to the sample found at the scene wou…

Forensics never relies on a single piece of evidence. It takes several corroborating accounts and pieces of evidence to reach "beyond reasonable doubt."

This is why even breathalyzers have to be done twice, with a gap in between (and preferably with different sensors). It's also why several witnesses are examined. It's why fingerprints and lie detectors alone don't pass the muster. Nearly anything can be faked, or misinterpreted. All these things have to be used together to create an unbreakable story.

So there is next to no risk with DNA in the air.

As an example, there recently was a guy who went into a police station and claimed that he was relocating there from another province. The officer on duty was suspicious, and found there was no record of this officer in the entire country, and arrested him. In court, the guy got off the hook, even after impersonating a police officer and trying to infiltrate a station, because the officer on duty did not collect the appropriate evidence. The camera footage looked entirely normal. It became entirely hearsay.

You can pretty much expect him to charge that officer with wrongful arrest now.

We may never know what that guy was up to. But he certainly had chutzpah!

Re: Air is full of DNA

#56

Post by ksaj »

People thinking how complicated this must be to filter through for forensics, forget that during and following the Covid lockdown, cities monitored sewage water for Covid viral load. They even recognized and reported the specific strains and their dominance in the samples. This includes finding "new" strains, and all this among all the other DNA/RNA bits to be found in city sewage.

So the technology is indeed there to find the needle they're after in the haystack they're provided.

Re: Air is full of DNA

#57

Post by SiempreViernes »

etiam wrote: post #47
cwmoore wrote: post #43

Earlier quoted context omitted.

No need to wonder if you study the lymphatic system.

Maybe so, but also maybe not quite my point, unless you know something I don't about it. Sure, some samples will be off to antigen presentation, but does that inform more than this is an encountered foreign substance and this is how to bind to it for neutralization ? Seems like in principle you could take the overview picture and have something like olfaction, but for things that hadn't been sufficiently cracked open…

If the quantities are too low for the nose to pick them up I think nature has converged on "too noisy to bother with".

Re: Air is full of DNA

#58

Post by pfdietz »

throwaway27448 wrote: post #54
pfdietz wrote: post #53

Earlier quoted context omitted.

I meant, "we have no DNA evidence from non-avian dinosaurs". Saying that birds have the same DNA as birds is not evidence of much of anything. :)

I think the genetic distance from crocodiles is still pretty strong evidence.

That just shows they diverged from crocodilians after that clade diverged from turtles. It doesn't show birds and dinosaurs are more closely related to each other than birds are to crocodilians (but the fossil evidence shows that.)

Re: Air is full of DNA

#59

Post by duped »

ksaj wrote: post #55
azalemeth wrote: post #19

I do often wonder about stories like this in the context of forensic science – my (incomplete!) understanding a lot of the time suspect DNA samples are taken from small areas and amplified significantly with high-cycle count PCR. I'd worry that any jury presented with a statistical argument about a fragment of somebody's DNA being very unlikely ("1 in 100 million") to be different to the sample found at the scene wou…

Forensics never relies on a single piece of evidence. It takes several corroborating accounts and pieces of evidence to reach "beyond reasonable doubt." This is why even breathalyzers have to be done twice, with a gap in between (and preferably with different sensors). It's also why several witnesses are examined. It's why fingerprints and lie detectors alone don't pass the muster. Nearly anything can be faked, or mi…

> Forensics never relies on a single piece of evidence

An uncharitable characterization is that forensics relies on many pieces of _stuff_ that cops and attorneys can reasonably convince a judge meets the rules of evidence and a jury that it is in fact evidence, while hoping the defense can't afford an expert (mind you, almost never a practitioner, but a professional legal consultant) to convince the jury it isn't evidence.

Most forensic analysis is complete bullshit, and it takes decades to convince judges to forbid the junk science.

So I wouldn't say there's "no risk." There's tons of risk.

What I would add is that you almost never have to worry about forensics if you're committing crimes, because the forensics are only going to be used to prove your guilt in court should you choose to fight it. If you're not committing crimes and become the focus of an investigation, you should be terrified of forensics.

Re: Air is full of DNA

#60

Post by etiam »

SiempreViernes wrote: post #57
etiam wrote: post #47

Earlier quoted context omitted.

Maybe so, but also maybe not quite my point, unless you know something I don't about it. Sure, some samples will be off to antigen presentation, but does that inform more than this is an encountered foreign substance and this is how to bind to it for neutralization ? Seems like in principle you could take the overview picture and have something like olfaction, but for things that hadn't been sufficiently cracked open…

If the quantities are too low for the nose to pick them up I think nature has converged on "too noisy to bother with".

Are the quantities too small though? Really foul-smelling small molecules can be sensed at least down to ppb concentrations. And the recent technical use of "eDNA" demonstrates there's signal to be had.
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