Photograph by Michael Nichols, National Geographic
Posted on 06/28/2013 8:13:52 AM PDT by null and void
Well-preserved specimen pushes back the timing of modern horse evolution.
A group of Przewalski's horses, once considered extinct in the wild.
Photograph by Michael Nichols, National Geographic
Photograph courtesy D.G. Froese via Nature
DNA shines a light back into the past, showing us things that fossils can't. But how far back can that light extend?
Some of the oldest DNA sequences come from mastodon and polar bear fossils about 50,000 and 110,000 years old, respectively. But a new study published online today in the journal Nature reports the latest in the push for recovering ever more ancient DNA sequences. Samples from a horse leg bone more than 700,000 years old have yielded the oldest full genome known to date.
"We knew that sequencing ancient genomes as old as 70,000 to 80,000 years old was possible," said Ludovic Orlando, an evolutionary geneticist with the Natural History Museum of Denmark at the University of Copenhagen. "So we said, why not try even further back in time?"
The Pleistocene horse genome Orlando and colleagues pieced together helped them determine that the ancestor to the Equus lineage—the group that gave rise to modern horses, zebras, and donkeys—arose 4 to 4.5 million years ago, or about two million years earlier than previously thought. (Learn more about the evolution of horses.)
The ancient horse genome also allowed the team to determine the evolutionary relationship between modern domestic horses and the endangered Przewalski's horse, a native to the Mongolian steppes that represents the last living breed of wild horse.
The team found that Przewalski's horses were an offshoot of the lineage that gave rise to domestic horses. The two groups diverged around 50,000 years ago.
Once considered extinct in the wild, Przewalski's horse was re-introduced into the wild from a captive population of only a few dozen. While this number suggests that the genetic diversity of the species might be too small to support, the study shows that Przewalski's horses are in fact more genetically diverse than domestic breeds such as Arabian and Icelandic horses.
"We think that there's enough genetic diversity within the Przewalski's horse to keep conservation efforts viable," Orlando said.
Cold Storage
Extracting ancient genomes from long-dead samples is labor intensive, and there is a limit to how far back one can go.
Studies on the half-life of DNA suggest that even under ideal circumstances, DNA sequences older than 1.5 million years will be too short to be readable. So it's highly unlikely that DNA will be recovered from dinosaurs, since they disappeared 65 million years ago, except for the lineage leading to modern birds.
But the preservation environment of an ancient sample can help extend the amount of time DNA has before it degrades past the point of being recoverable.
"Cold is good," said Orlando. Frozen is even better, because liquid water isn't present to degrade DNA molecules.
The six-inch (15-centimeter) horse leg bone the team analyzed originated in the Yukon Territory of western Canada. Permafrost kept the remains in a kind of cold storage for about 735,000 years until scientists dug it out in 2003.
To determine whether there might be any biological molecules left in the sample, Orlando and colleagues first looked to see if they could spot amino acids from collagen—a protein found in bone—in the specimen.
Once they identified and successfully sequenced those proteins, the researchers moved on to trying to extract DNA from the ancient leg bone.
As is the case with the majority of ancient fossils, most of the DNA they found was from bacteria that had populated the bone after the horse died. Using DNA from modern horses as a reference, the team was able to identify "endogenous" DNA that belonged to the ancient horse itself.
"We sequenced 12 billion DNA molecules, of which 40 million [were of] horse origin," said Orlando. "There was a bit of horse DNA in an ocean of microbial DNA."
A New World
The recovery of a genome almost an order of magnitude older than any previous genomic information opens up a wide range of new targets for studying fossils at the genetic level, possibly including ancient human species, if they lived in cooler environments.
"You name it—what are your favorite Pleistocene beasts?" wrote Hendrik Poinar, an evolutionary geneticist at McMaster University in Ontario, Canada, in an email.
Poinar, who was not involved in the current study, would like to see this applied to elephant evolution. "This should address issues related to the origin of hair and size plasticity and how they adapted to very different ecologies."
He was not surprised that researchers were able to sequence a complete genome from 700,000 years ago. It just takes time and money, Poinar said.
But he also points out that sequencing ancient genomes is more about preservation in various environments than the age of a specimen. "I am sure there will be older genomes soon enough."
Radiate?
That was last week. They've evolved since then.
Nope ... I only knew about radium watch dials that were found to be dangerous and it was stopped.
If basic research adds to our stock of knowledge it is worthwhile. That’s why you do basic reserch even if the knowlege doesn’t make a whit of practical difference.
I really shouldn’t have to explain that to a PhD in molecular biology.
So you’ve never had a broken bone x-rayed, never needed radiation therapy, never had a radio iodine uptake test, or a thallium heart scan, never been on an airplane whose critical turbine parts were inspected with x-rays, never used a single watt generated in a nuclear power plant, never been defended by a nuclear powered submarine, know no-one descended from a serviceman who would have died on the Japanese mainland had they not surrendered?
Each of those is a direct result of a useless, purely academic 19th century study of radium.
And radium itself? It still sees some use in treating metastasized bone cancer.
Nonsense!
Last week it was:
“but but but the entire universe is only 6016 years, 6 months, 15 days 1 hour and 16 minutes old”
When I was born 59 years ago I had a birth mark on by one of my knees. I’ve been told they put radium needles on the site to, well, I’m not sure what they were thinking.
I have a small scar there now. No adverse consequences yet that I know of.
“but but but the entire universe is only 6016 years, 6 months, 15 days 1 hour and 16 minutes old”
How can you be sure it was last week? All dating methods have been proven to be unreliable.
Except Primate of All Ireland Ussher, of course...
:)
Obviously a sober and studious man...
Well, it is business hours.....
Not in Ireland, unless your business is a pub...
Unfortunately, I’m not, and it isn’t, so back to my studies I go.
“If basic research adds to our stock of knowledge it is worthwhile. That’s why you do basic reserch even if the knowlege doesn’t make a whit of practical difference. I really shouldn’t have to explain that to a PhD in molecular biology.”
Of course many great discoveries resulted from trivial investigations. But, there is enormous waste in academic research. Very few within these disciplines are willing to state this. Resource allocation is an important issue in an era of limited resources. We simply cannot study anything and everything for the sake of adding to our “stock of knowledge”. If you don’t agree then you sanction departments of women’s and Africana studies, or BS investigations into environmental studies that are more political then scientific. Even basic molecular biology is laden with silly and unimaginative projects.
'COURSE I've had an x-ray ... but as far as I know, none of the rest.
I have no idea (nor do you) WHERE my electricity comes from .. and you somehow think I'm an enemy of research?
This all started with the genomes of ancient horses and you've got me denegrating WW2 vets and their offspring?
GFY, n&v.
Any hard science research that adds to our understanding of the physical world has merit. None of it is silly. How you evaluate any piece of research in the scheme of things depends on your intests.
And even if you insist on judging research by what useful technology it spawns, you can never tell. A seemingly insignificant finding might be the first link in a long chain that ends in a world changing finding. Or a piece of research might sit on a shelf for a century until some new discovery makes it vital.
In mathematics (not physical but a hard science) boolean logic was a pure abstract concept with no practical use in the real world. Any layman looking at Boole's work would have called it silly, a waste of time. Until people started thinking about automatic computing. Then it became core of the technology that civilization is built on.
No, no hard science research is silly.
About what I’d expect from someone who boasts that they didn’t read the article.
You did manage to read quite a few things that were not in my reply, and attribute what you read into it as my malice.
Have a nice day.
(s) offspring of a WWII vet, Pacific theater, Okinawa, Semper Fi!...
Note: this topic was posted 6/28/2013. Thanks null and void.
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