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."
This post should be tagged for “evolution” territory.
Always feel free to add any keyword you deem appropriate.
If, after studying all of this, they admit that there is not much variation or difference in the two horses ... stop the funding and go find YETI
“... I see no point in the research other than curiosity.”
Exactly. Much government-funded research is playground stuff. Scientists having fun with other people’s money, but realizing no tangible benefit to society.
Eohippus (meaning "dawn horse") was the earliest-known horse ...I assume 4 in the front and 3 in the back doesn't meet your high standards.This primitive horse had 4 hoofed toes on the front feet and 3 hoofed toes on each hind foot.
People said the same thing when a few people started playing with radium containing rocks in the 1800’s
Well, this research was not done here, it was Denmark. This type of research is not necessarily “playground” stuff either. This could lead to extraction and characterization of extremely ancient human DNA as well. Being able to track, characterize and understand changes and mutations in a species genome across the span of history can lead to insights that could identify reasons for certain diseases and lethal mutations in humans today and possibly provide a path for correcting those problems and/or curing some diseases. Basic research is the groundwork for more specific and useful research and breakthroughs.
“Basic research is the groundwork for more specific and useful research and breakthroughs.”
Understand your thoughts, fully. I have a basic science PhD in molecular biology, and an MD. But it’s impossible to refute your argument except to say one can always claim every seemingly trivial or esoteric discovery could change the world. But 99% won’t. Your argument cannot justify unlimited funding for very average ideas and scientists. There has to be a limit.
I would if I could, but ... can’t seem to do it. Moderator might do it for us.
If indeed horse DEvolved from 4 to one toe ... and it's ANY indication of anything ... I'd get on my knees and ask Jesus to save me before I lost my mind.
and what does radium do today ???
Could, maybe, might ... what makes anyone think we’re going to be around the hundreds of years (from now) when it all MAY come to fruition ?
From Jones' "Introduction" we have ...
"For the past two decades the nation has lived through an episode that has, with extraordinary speed, laid bare the argument of The Origin of Species. The organism involved was unknown in the ninteenth century, but is now familiar. It is the AIDS virus."
The rest of the book is a modern update of every chapter in Darwin's "Origin."
Hmmmm. I simply clicked on “Click to Add Keyword” and typed it in.
I didn’t see any particular need to attract the “but but but the entire universe is only 6016 years, 6 months, 22 days and 37 minutes old” crowd.
They and their anti-science/Luddite ilk seem to have no difficulty finding these threads without any additional help.
That's a surprise.
If indeed horse DEvolved from 4 to one toe
It did.
... and it's ANY indication of anything ...
It is.
I'd get on my knees and ask Jesus to save me before I lost my mind.
No comment.
The study of radium containing rocks lead to a few useful things.
I bet you don't know of a single one, do you?
An old man should never plant a tree.
The fruits won't appear until he is dead.
Useful lumber won't be available until his children are old.
No point. No point at all.
False alarm. It’s just Hillary. All that horse manure fooled us.
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