Palaeogeneticist Morten Allentoft used the bones of extinct moa birds to calculate the half-life of DNA.
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From Nature magazine
Few researchers have given credence to claims that samples of dinosaur DNA have survived to the present day, but no one knew just how long it would take for genetic material to fall apart. Now, a study of fossils found in New Zealand is laying the matter to rest — and putting paid to hopes of cloning a Tyrannosaurus rex.
After cell death, enzymes start to break down the bonds between the nucleotides that form the backbone of DNA, and micro-organisms speed the decay. In the long run, however, reactions with water are thought to be responsible for most bond degradation. Groundwater is almost ubiquitous, so DNA in buried bone samples should, in theory, degrade at a set rate.
Determining that rate has been difficult because it is rare to find large sets of DNA-containing fossils with which to make meaningful comparisons. To make matters worse, variable environmental conditions such as temperature, degree of microbial attack and oxygenation alter the speed of the decay process.
But palaeogeneticists led by Morten Allentoft at the University of Copenhagen and Michael Bunce at Murdoch University in Perth, Australia, examined 158 DNA-containing leg bones belonging to three species of extinct giant birds called moa. The bones, which were between 600 and 8,000 years old, had been recovered from three sites within 5 kilometres of each other, with nearly identical preservation conditions including a temperature of 13.1 ºC. The findings are published today in Proceedings of the Royal Society B.
Diminishing returns
By comparing the specimens' ages and degrees of DNA degradation, the researchers calculated that DNA has a half-life of 521 years. That means that after 521 years, half of the bonds between nucleotides in the backbone of a sample would have broken; after another 521 years half of the remaining bonds would have gone; and so on.
The team predicts that even in a bone at an ideal preservation temperature of −5 ºC, effectively every bond would be destroyed after a maximum of 6.8 million years. The DNA would cease to be readable much earlier — perhaps after roughly 1.5 million years, when the remaining strands would be too short to give meaningful information.
“This confirms the widely held suspicion that claims of DNA from dinosaurs and ancient insects trapped in amber are incorrect,” says Simon Ho, a computational evolutionary biologist at the University of Sydney in Australia. However, although 6.8 million years is nowhere near the age of a dinosaur bone — which would be at least 65 million years old — “We might be able to break the record for the oldest authentic DNA sequence, which currently stands at about half a million years,” says Ho.
The calculations in the latest study were quite straightforward, but many questions remain.
“I am very interested to see if these findings can be reproduced in very different environments such as permafrost and caves,” says Michael Knapp, a palaeogeneticist at the University of Otago in Dunedin, New Zealand.
Moreover, the researchers found that age differences accounted for only 38.6% of the variation in DNA degradation between moa-bone samples. “Other factors that impact on DNA preservation are clearly at work,” says Bunce. “Storage following excavation, soil chemistry and even the time of year when the animal died are all likely contributing factors that will need looking into.”
This article is reproduced with permission from the magazine Nature. The article was first published on October 10, 2012.
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23 Comments
Add CommentI don't know if I'm relieved or disappointed.
Reply | Report Abuse | Link to thisI'm a little disappointed, but at least we can still obtain viable DNA from creatures that have gone extinct relatively recently. I believe we should do research to find out what the best conditions are for preserving DNA, as that may become valuable information in the future.
Reply | Report Abuse | Link to this"The team predicts that even in a bone at an ideal preservation temperature of −5 ºC, effectively every bond would be destroyed after a maximum of 6.8 million years."
Reply | Report Abuse | Link to thisWell, that still leaves us hope for restoring many other critters like the wooly mammoths etc. GK
I hate to pick a nit, but I was stuck on trying to understand what was meant by the last sentence of the opening paragraph:
Reply | Report Abuse | Link to this"Now, a study of fossils found in New Zealand is laying the matter to rest — and putting paid to hopes of cloning a Tyrannosaurus rex."
I'd never heard the phrase "putting paid to" & had to search to find that it's primarily a British & New Zealand colloquialism...
Editors: this article may have originated in Nature, but this is Scientific American, correct?
Welcome to the Internet, where you're exposed to more culture than your own...
Reply | Report Abuse | Link to thisIf that bone he is drilling is from a bird; that would be one really “Big Bird”.
Reply | Report Abuse | Link to this@ jtdwyer
Reply | Report Abuse | Link to thisFor your information:
"Nature is the world's most highly cited interdisciplinary science journal, according to the 2010 Journal Citation Reports Science Edition (Thomson Reuters, 2011)."
You're seriously suggesting that Nature magazine publish a separate issue translated for American readers? Perhaps we English speakers outside the US should expect the same of Scientific American?
Get real! (for Non Americans, "get real" is an American expression meaning "be sensible").
So what? so called "scientists" can still read the DNA code, we don't need viable DNA to copy it, we can still make a "pursuadosaure" by backward genetically engendering, devolving birds to recreate dinos.
Reply | Report Abuse | Link to thisHey, this means that we've got a shot at fixing the screw-up that we made of this planet and all of the recently extinct Holocene and latest Pleistocene species that we ate! Awesome!
Reply | Report Abuse | Link to this"The team predicts that even in a bone at an ideal preservation temperature of −5 ºC, effectively every bond would be destroyed after a maximum of 6.8 million years. The DNA would cease to be readable much earlier — perhaps after roughly 1.5 million."
Reply | Report Abuse | Link to thisWhile this might mean that dinosaurs won't ever be cloned, it is reassuring to know that there are many very interesting organizations that are well within this range, such as ground sloths, mammoths or Paraceratherium rhinos, which went extinct well within that range and include some of the largest known mammals in history.
Also, this article seems to indicate that enzymes will unavoidably break down bonds, but microorganisms speed decay and in the long run "reactions with water are thought to be responsible for most bond degradation."
Reply | Report Abuse | Link to thisMost critically, the study seems to presume that
"Groundwater is almost ubiquitous, so DNA in buried bone samples should, in theory, degrade at a set rate."
While these conditions may be "almost ubiquitous", it seems there may be some conditions that could preserve DNA for much long periods, especially those that may exclude microorganisms and water. In particular, I wonder whether these results apply at all to, for example, tar pits? Perhaps there are some special preservation conditions that could sustain DNA bonds for several million years...
Useful information. They were extremely fortunate to have found the samples as they did for study. It is too bad scientists can not recreate Rex and Jurassic Park, but as an author such technicalities won't.
Reply | Report Abuse | Link to thisSlight correction necessary: Paraceratherium went extinct in the mid-Miocene, *around* 15 MYA (I can't remember exactly). Also, what about the recently extinct species (those that went extinct after the close of the Ice Ages)? I don't know about you, but if I could clone a dodo, or a death-eagle (*Harpagornis moorei*), or a bunch of moas, or even one of the Mascarene tortoise species, or any other species that was driven extinct directly by humans, I would do them first and look into ground sloths and mammoths later.
Reply | Report Abuse | Link to this@jtdwyer
Reply | Report Abuse | Link to thisGiven the choice between the Sci Am editors tidying up unfamiliar colloquialisms, or leaving them intact and allowing me to not only learn the information presented but also the richness of the common language we share with the authors, I would opt for the latter.
Passenger Pigeon anyone?
Reply | Report Abuse | Link to thisYeah, my mind went to passenger pigeon, dodo bird, moa bird, and then any of the hominids from up to 1 million yeas old. I think the ethics of such an endeavor are probably questionable to say the least, but it would be amazing to see Homo Neanderthalensis and Homo Erectus alive and available for study.
Reply | Report Abuse | Link to thisHere is a nut to ponder for you all:
Reply | Report Abuse | Link to thisIf anyone was so inclined why not De-evolve the genetic material which survives in beasts around the world and that within ourselves for that matter. We have the tech now do we not? Gene expression, Mendelian genetic, Darwinism ...go go gadgets. All of the past is within the gene codes every living thing has on this planet.
I still have the hallmarks via this Neanderthal-ish forehead I sport today.....just say'in...
Umm...You seem to be harboring the misconception that evolution is a "ladder of progress" with humans at the top. It is currently impossible to "de-evolve" species as you say, and in any event most if not all of the best targets for revivification were not the ancestors of extant species.
Reply | Report Abuse | Link to thisAlso, Neandertals were not "primitive" modern humans, but a wholly different species that was well-adapted for hunting large prey, as opposed to the mid-size ungulates favored by early modern humans.
For several reasons, most importantly their likely inability to comprehend abstractions and likely difficulty inventing and accepting new tools and ways of doing things, Neandertals would not fit in well in modern society. The most progressive ones would be the people just getting their first cordless phone as the iPad2 comes out.
Finally, if you want to try to revivify something like a saber-toothed cat, be my guest, but remember "Jurrasic Park". It would probably be smarter to do Reunion starlings (*Fregulipus varius*) and make a fortune in the pet bird market (the starling was easily tamed, easily fed, and sang sweetly).
Hmmm, several genera of the saber-toothed cat fall within the range of viability. Let's get on that, shall we?
Reply | Report Abuse | Link to thisRaphus cucullatus might also be an interesting species to bring back. But they were such dodos. They'd probably go and make themselves extinct all over again.
Yeah, it would be a whole lot of fun to have *Homotherium serum* wandering the praries. Hillbilly-B-Gone Maximum! They can't deny evolution if they're literally seeing part of the past.
Reply | Report Abuse | Link to thisAs to your second para; decent joke, but dodos weren't stupid, just not used to humans.
So did the canary, sing sweetly, that is, until the government ordered the cannabis seed removed from its bird seed. That may be an urban myth, but I like it anyway.
Reply | Report Abuse | Link to thisThe aseveration that DNA has a 521 years half-life may be in conflict with some info published before, for example, an important part of the Neandertal and Denisovians non-sapiens human beings genome having been identified and sequenced; even more, one never knows (Or somebody already knows this?) how the substances and materials DNA may be wrapped in, for example amber, influence its preservation. You get surprises in this field in unexpected places, probably the subject deserves a deeper and less pessimistic approach.
Reply | Report Abuse | Link to thisThat's a nano-nit. And yep, you sure did have to pick it.
Reply | Report Abuse | Link to this