More to the point is that we are recapturing million year old
genomes. This implies that our efforts in the Yukon Placers will
likely provide the entire Pleistocene menagerie for reconstitution.
This is an amazing advance and first on the agenda will be the
mastodon of course.
It may turn out to be harder to recover isolates from islands only a
couple of centuries extinct than the whole Pleistocene.
This whole field is on the verge of becoming extremely popular. One
mastodon or mammoth should suffice. We will not want huge gherds of
these creatures, but they also have their place as we know from
Africa.
First horses arose
4 million years ago
The oldest full genome
sequence, recovered from ancient horse bone, pushes back equine
origins by 2 million years.
Erika Check Hayden
26 June 2013
The Przewalski’s
horse, recently brought back from the brink of extinction in
Mongolia, is truly the last remaining wild horse, suggests the new
study.
The
humble horse has provided the oldest full genome sequence of any
species — from a specimen more than half a million years old, found
frozen in the permafrost of the Canadian Arctic. The finding,
published in Nature today1, pushes back the known origins
of the equine lineage by about 2 million years, and yields a variety
of evolutionary insights.
The
sequence was extracted from a foot bone of a horse that lived between
780,000 and 560,000 years ago. By sequencing the animal's genome,
along with those of a 43,000-year-old horse, five modern domestic
horse breeds, a wild Przewalski’s horse and a donkey, researchers
were able to trace the evolutionary history of the horse family
in unprecedented detail. They estimate that the ancient ancestor of
the modern Equus genus, which includes horses, donkeys and
zebras, branched off from other animal lineages about 4 million years
ago — twice as long ago as scientists had previously thought.
“We have beaten the time barrier,” says evolutionary biologist Ludovic Orlando of the University of Copenhagen, who led the work with colleague Eske Willerslev. Noting that the oldest DNA sequenced before this came from a polar bear between 110,000 and 130,000 years old2, Orlando says: “All of a sudden, you have access to many more extinct species than you could have ever dreamed of sequencing before.”
“We have beaten the time barrier,” says evolutionary biologist Ludovic Orlando of the University of Copenhagen, who led the work with colleague Eske Willerslev. Noting that the oldest DNA sequenced before this came from a polar bear between 110,000 and 130,000 years old2, Orlando says: “All of a sudden, you have access to many more extinct species than you could have ever dreamed of sequencing before.”
The team was able to
sequence such old DNA partly because of the freezing ground te
But the researchers
were also successful because they had perfected techniques for
extracting and preparing the DNA to preserve its quality for
sequencing. They targeted tissue within the fossil which has high DNA
content, such as collagen. They also combined DNA sequencing
techniques to get maximum DNA coverage — using routine
next-generation sequencing with single-molecule sequencing in which a
machine directly reads the DNA without the need to amplify it up
which can lose some DNA sequences.
Now, a major challenge
for the field is to apply these techniques to other species such as
ancient human species, including Homo heidelbergensis and Homo
erectus, which lived hundreds of thousands to more than 1 million
years ago. But such specimens are unlikely to be found buried in the
DNA-preserving permafrost.
”The real challenge
right now in the field is combining these next-generation sequencing
technologies with the possibility of analysing non-permafrost
samples,” says Carles Lalueza-Fox, a palaeogeneticist at the
Institute of Evolutionary Biology in Barcelona, Spain.
Wild horses
Orlando and
Willerslev's paper hints at the other types of discovery that these
technologies can enable. Their team, for instance, was able to
support the contention that the Przewalski’s horse (Equus ferus
przewalskii), which was brought back from near-extinction in Mongolia
by captive-breeding programmes, is truly the last remaining wild
horse when compared genetically with domesticated horses.
The researchers were
also able to trace the size of the horse population over time by
looking for genomic signatures of population size, and were thus able
to show that populations grew in periods of abundant grassland, in
between times of extreme cold.
But that is not
surprising. Other researchers say that it is a proof of principle for
how similar studies can be used to explore the factors that have
driven evolution and speciation. “This kind of study is giving us
novel views that show us the nuts and bolts of how evolution is
working,” says Alan Cooper, director of the University of
Adelaide's Australian Center for Ancient DNA.
Although Willerslev and Orlando say that it would theoretically be possible to resurrect the ancient horse by implanting a modern horse egg with the ancient DNA, they have no plans to do so. They say that it has been a formidable task just to assemble the genome from many small fragments of DNA. For now, they prefer to focus on further improving their techniques, before testing them on other samples.
When they have
mastered the technique, Willerslev predicts that it will have a huge
impact on evolutionary biology. “Ancient genomics will change a lot
of the ways we look at evolution to date,” he says.
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