It used to be so uncomplicated. DNA is the stuff that makes you who you are. It’s what makes you look the way you do, makes you susceptible or resistant to certain types of illnesses, even sets your biological clock. DNA is the stuff of life.
Except when it’s not. As science probes the depths of the genomes of all forms of life on Earth, we are confronted with an increasingly-convoluted relationship between DNA and it’s expression – nature and nurture, in other words – that in turn makes our previous use of DNA increasingly dubious.
It isn’t all bad news: our more sophisticated understanding of genetic information means we’re getting close to finding cures for disease, genetically-tailored health care and amazing discoveries in the worlds of biology and anthropology. But our colloquial understanding the nature of DNA has not caught up to the scientific understanding. The result of this gap can often be abusive at best and flat out destructive at it’s worst.
Nowhere is that fact more certain than in the world of forensics. As DFE discussed last year, local law enforcement has seen the same forceful push-back on DNA evidence presented in criminal cases that has swept the nation in the last few years. The assumption most of the public has in the infallibility of DNA to finger guilty parties is entirely wrong. And whether intentionally or not, many cases have been tried and many people convicted on evidence that is nowhere near near as declarative as prosecutors would have you believe.
A new grant to Syracuse University is aimed at finding a solution to a fundamental problem in forensic DNA evidence-gathering: mixed DNA samples. Regardless of what type of tissue law enforcement is sampling from – blood, semen, hair, skin – it’s still just a pile goo at a crime scene. That pile of goo is a bit of a hothouse flower: organic chemicals don’t last long outside the body. And biological evidence can easily get mixed up with other that of individuals not even involved in the crime. Taken together, you can see that this is a bit of a dumpster dive.
So clearly, the biggest challenge in DNA forensics is getting a clean, uncontaminated and complete sample of DNA. How challenging? Basically, the odds of meeting all three criteria are just a few degrees north of ever french kissing a unicorn. Pretty low.
The SU plan is to light up cells with dyes and black light in a way that lets them tell whether the two cells contain the same DNA. The next step would be to extract them by DNA signatures: all of Specimen X, followed by Specimen Y and so on. That’s where SU’s brain power is supposed to hopefully kick in.
And even as the scientific community grapples with the problem of commingling DNA and incomplete samples, a novel and highly-dubious use of DNA evidence is being tested in law enforcement, winkingly called “Familial DNA.” This concept means that, even if you’ve never been DNA tested for any reason, your DNA may get linked to a crime, simply because there is DNA in a database from a cousin or other relative.
What? That’s right. If a DNA sample taken at a crime scene is similar enough to a relation of yours, police may use this fact to posit that the DNA must be yours. In a Six Degrees of Separation type of scheme, you are implicated to be involved in the crime simply because you have similar DNA to what was found on scene.
This deeply-troubling practice runs directly afoul of the Birthday Paradox, a statistical quirk that radically and unexpectedly reduces the odds that a match will be found in a group, rather than individually. For a much more elegant explaination than I might summon forth, read Southern Fried Science. This statistical fact makes DNA databases generally misleading in the first place, but once you expand the search to include people who aren’t even in the database, the potential results are genuinely disturbing.
In the world of anthropology (the science, not the store), our deepening understanding of mitochondrial DNA is completely redefining our understanding of human migration. Perhaps not for the better, depending on your favourite theory.
At issue is the long-held belief that those who would become Native Americans traveled across the Land Bridge and very quickly populated the whole of the Pacific shore. This fairly linear theory of American anthropology has brought multiple theories and timelines into clash for decades. Are the Clovis points really the most ancient relics? No. But are the Clovis people still the oldest people in the Americas? Well, maybe…
What the newest mitochondrial DNA evidence, taken from the bones of a mother and child discovered near the Bering Sea, suggest that perhaps part of the problem with identifying the path of Native Americans is that there simply isn’t just one path.
Instead, the mitochondrial evidence points to a highly-diverse group of Asian immigrants coming across the famed land bridge. Rather than a single set of tribes or related individuals crossing the great divide, it may have been hundreds. This new evidence suggests that the reason archeological evidence of human inhabitation seems so scattered is because human habitation was in fact very scattered.
If there is a lesson in the week’s DNA news stories, it is that science is a double edged sword for those that would hold onto it’s truths too tightly. However reliable a scientific fact has seemed in the past, there is always new research that casts doubt upon it.
