Why did it take so long before DNA was used in forensics?

Okay, so it was fifty years ago that Crick and Watson* determined the structure of DNA (with help, credited or uncredited, from Pauling, Franklin and Wilkins). AFAIK, and I could very well be wrong, it wasn’t until the early '90s that it became possible to use DNA to determine identity :::cough:::OJ:::cough:::. Why did it take so long to get to that point? And what other uses were found for this knowledge in the interim?

I’m wording this all wrong, I know, but I hope some medical-science-type-person can understand what I mean.

*And Watson was only 25 at the time, which might partially explain why he was such a jerk. Although he was 40 when he wrote his book.

Although Crick and Watson made their discovery in 1953, it wasn’t until the 1980s that it was determined that most DNA varied from one person to another. In 1983, Sir Alec Jeffreys developed the first DNA profiling test, and it all went from there.

Some of the other milestones in the DNA story are here.

It also needs to be noted that there was a great deal of political pressure against forensic DNA analysis, using the exact same arguments that were used against fingerprints a century or so before.

One of the big breakthroughs was the invention of the Polymerase Chain Reaction, which allowed small samples of DNA to be multiplied to give sufficient quantity to be able to analyze. This technique became usable in about 1990-91.

Two factors related to the development of the tests: their cost, and what I’ll call the parameters of the tests (not being a science type, I don’t know if that’s the right term).

On the first point, I remember in the early nineties when DNA tests were starting to be considered. The tests were very expensive, so as a practical matter could only be considered for a major case, because it would have been too easy to blow the police budget if a lot of tests were ordered.

The second was the parameters of the tests: the time it took, the nature of the sample, and so on. The first tests that I remember reading about needed samples over a certain size, had to be of a certain freshness, and for best results, from certain body sites (e.g. - hair roots). As well, the tests took a long time to do. All of those parameters reduced the practical utility of the tests in crime investigation and courtroom proof.

What changed? the tests themselves. Over the past decade, the tests have got better and better. Ways have been found to “culture” the DNA, so that a small sample can be magnified to allow testing. Ways have been found to extract DNA from even very old samples, and from a wider range of bodily substances. The tests are now much quicker. And, as is the constant trend in applied science, just like computers the costs of the tests have dropped steadily. All of these changes add up to the tests becoming more practical and useful in a much broader range of cases.

Dogface, I’m not familiar with the political pressure you mention. Could you elaborate?

Purely speculating, I wonder if use of DNA was slowed by the idea, perceived or real, that such evidence might not be easily understood by a jury. Or course, even if that were the case it shouldn’t have had an effect on its use in the investigative process.

amarone has got it. The development of PCR enabled the testing of trace quantities of DNA. It was invented in the mid-1980’s and really only started taking off in the early 1990’s. As Northern Piper has said, techinques have gotten better over the past decade, allowing ever-smaller and older samples to be tested.

Of course that bit of technology would have been pretty useless without the discovery and exploitation of sequence specific restriction endonucleases from the 1970’s onward.

Thanks for the info!

And I would also like to know about the political pressure to which Dogface refers.

I know of no such political pressures which retarded DNA testing. It was always an issue of technology as far as I am aware.

A summary of the fight (now pretty much over) can be found in the first chapter of Coleman & Swenson. 1994. DNA in the Courtroom: A Trial Watcher’s Guide.

Can you summarize it even further, for those of us who don’t have time to find that book and read it? (Please?)

I thought all the major steps in discovery and application (in the criminal field) happened not a million miles from me, so I’d also be interested in Dogface’s “political pressure" as I’m not aware of any.

I guess if he’s being US-centric then there’s the usual Darwin vs. Creationist stuff to contend with - is that what you mean Dogface ?

I don’t know what sort of blind ignorance is driving the “Darwin vs. Creationist stuff” comment.

The opposition involved defense attorneys opposing the practice with prosecutors approving of the practice. More liberal press outlets (like the NY Times) presented the technique as fraught with so much uncertainty that it virtually guaranteed that the innocent would be convicted. That all opposed were defense attorneys definitely smacked of politicization. It never seems to have occurred to them that the technique could also be used to exclude the innocent from conviction or even exonerate the wrongly-convicted. This controversy was pretty much over by 1995 and all serious opposition stopped once the Innocence Project started using the technique to exonerate people.

As for not remembering any controversy–I refer folks to the notable short memory of the public. If a matter does not directly impinge on our lives, we forget it after a decade or so.