In 2013 a remarkable DNA sequence was revealed by geneticists studying ancient DNA. It was the nearly complete genome extracted and decoded from the remains of a tooth from a horse preserved in permafrost sediments buried in the Yukon region in Alaska. This partially fossilized bone was estimated to be more than 500,000 years old. This was the most complete sequences of an ancient sample yet produced.
I have written a series of posts about the origins of horses in the context of how young earth creationists (YECs) have sought to understand the origins of equine biological diversity. We have observed that many YECs have moved from denying the “horse sequence” of evolution to accepting that all living species of equines along with nearly 100 species of extinct horse-like species are all descendants of a common ancestor horse “kind.” But rather than this ancestor living 40 to 50 million years ago they believe this ancestor lived just 4500 years ago.
Given this YEC view of biological ancestry and what we might call rapid or hyper-evolutionary model we might ask: does this ancient horse DNA sequence might prove helpful to the YEC model or does it provide another problem, among countless others, that the YEC faces in their desire to draw up an alternative explanation for the observed biological diversity on earth?
Not long after the genome of this ancient horse was published Elizabeth Mitchell writing for the chief YEC apologetics ministry, Answers in Genesis, commented on this story. The title of her article is A horse is a horse, of course, of course. I wish she had read my article of a similar title (A horse is a horse, unless of course it isn’t a horse) which was originally published a few weeks before hers. She seems to have completely missed much of the implications of the horse genome with respect to young earth genetics model that I detail in my series of articles about horse origins (see links in the “Additional Reading” sidebar).
Let’s look at some of the implications of this ancient horse genome to the creationist’ model of biological origins and the age of the earth:
This horse is a horse and was a horse long ago: Here we have the sequence a horse that died long before the most recent Ice Age (we know this from the geological evidence were it was found) and that sequence clearly shows that this horse was a horse. By this I mean that this horse could easily be assigned the same species of horse, or very close sibling species, that we have today. This suggests that the species of horse from which domesticated horses are today was already distinct from other horse species (donkeys, zebras etc..) as long ago as 500,000 years. This is not what the YECs would predict about a horse sample found form before the last Ice Age.
Let’s start by looking at quote regarding horse evolution from George Purdom, AIG’s resident geneticist, which is included in Mitchel’s article:
While we would disagree that the horse ancestor lived millions of years ago (based on radiometric dating which uses unverifiable assumptions about the past), we would agree that all horses came from a common ancestor which, according to the Bible, was on the ark only around 4,300 years ago. The similarity of this fossil horse DNA to modern horse DNA further confirms that God created animals according to their kind (Genesis 1). There is variation within the kind, but even after the proposed hundreds of thousands of years the fossil and modern horse DNA are still very similar. We don’t observe the types of changes necessary for a horse to evolve into a different kind of animal.
A pair of the equine kind got off Noah’s ark about 4,300 years ago, and genetic information in that pair provided the raw material for all the equine varieties we see today. Speciation mediated through natural selection and other means enabled their descendants to adapt to many environments in the post-Flood world.
First, lets observe the obvious by important point that what we have here is more confirmation that AIG’s current thinking is that all horses (donkeys, asses, zebras, domestic horses and wild horses) are all the descendants of a pair of equine ancestors on Noah’s ark. So at one time there were no zebras, donkeys or horses but some sort of combination of all of them into just two individual animals that are the common ancestors of all of them.
Second, Dr. Purdom is very confused about the meaning of the lack of sequence divergence in this fossils horse. Elsewhere, Purdom calls this diversification from a common ancestor “genetic sorting of raw material.” So how much raw variation was there in this pair and where is the evidence that only a short time ago donkey’s, domestic horses, zebras, etc.. didn’t exist but only a single ancestral equine-like pair? This ancient DNA sequence of a horse provides us with some clues about how long the different horse species have been distinguishable as separate horse lineages/species.
Examining the figures I have included you can see that the Thistle Creek (the permafrost fossil sample we are focused on here) horse exhibits the greatest genetic differentiation (ie. more DNA differences as visualized as longer lines connecting them to other horses) than all the other horses though it is still clearly grouped with domesticated horses and the wild horse (Przewalski’s horse) rather than the more genetically distinct donkey and not shown zebras.
At first sight the YEC including Dr. Purdom, may think that a horse sequence that hasn’t changed much over thousands of years might support their view of lack of ability of species to change much today. But taking a minute to reflect further it quickly becomes clear that this ancient horse is of no help to the YEC. If a horse has been a horse for thousands of years how can the YEC claim that horses have a common ancestor with donkey’s, zebras etc… just 4500 years ago?
The second figure shows genetic variation in mitochondrial DNA for many living horses and quite a few “ancient” horses sample (bones from archaeological sites). Only the Thistle Creek, labeled TC, and 34,000 year old bone show sequences that are significantly divergent from all other horses. Even so these fossil sequences along with many other horse bones conventionally dated to more than 5000 years old still have DNA sequences that are clearly very similar to living horses.
In the YEC chronology the 5000 year, 43000 year and 500,000 year old samples would all be less than 4500 years old. But we have a reference point that YEC should agree limits the age of the fossils. The later two samples are found underneath Ice Age deposits. Therefore in the YEC chronology these bones must be older than 4000 years. If this is the case when the ancestor of all horse species got off of Noah’s Ark 4350 years go it must have diversified into horses, horses, donkeys, zebras and all species of extinct horses in just a few hundred years. How did the genomes of the two common ancestors on the ark get “sorted out” into the very distinct genomes we find in horses, zebras and donkeys today in just a few hundred years? Why are there no ancient horses with genomes that are mixed between donkeys and horses? And why, even if they were changed quickly, have horse genomes barely changed in the past 4000 years after undergoing radical change in just a few hundred in their model?
The ancient DNA sequence of this ancient horse is perfectly consistent with the expectations of modern genetics. It is consistent with the rate of genetic change we observe in the present and thus fit the conventional dating of the fossil being hundreds of thousands of years old.
Creationists believe is ultra-high speed evolution of species from a common ancestor but they have yet to provide any evidence (genetic models or ancient DNA samples) that provide any hint that this rapid divergence has actually occurred in the last 4500 years.
Does DNA preserved for 500,000 years support a young-earth or ancient earth?
A second questions is raised about the report of this ancient DNA genome sequence. Mitchell is quick to cast doubt on the conventional ancient age of the horse fossils. She references what she thinks is a problem with DNA preservation and her expectation that DNA molecules should not be able to survive 500,000 years and so she thinks this is evidence that these fossils are young. But as I have written before many times, (see: Where’s the DNA? Young Earth Creationism and the Search for Ancient DNA) even if ancient DNA were a problem for an ancient earth, and it doesn’t appear to be, this ancient DNA raises a significant problem for Mitchell’s young-earth viewpoint.
If the world is only a few thousand years old why is DNA not found in abundance in all fossil teeth not just ones from the very top of the fossil record? Rather than abundant in fossils, DNA is very difficult to find intact. No dinosaur teeth have DNA and yet we could pull the entire genome of mammoth from nearly every mammoth tooth we have every found. What Mitchell doesn’t tell her readers is that the DNA from the 500,000 year old horse was not in good shape at all but was fractured into mostly small 10-50 base pair fragments for which fancy repair enzymes had to be fashioned to “fix” DNA damage before even those short fragments could be sequenced. This is exactly what would be expected if this DNA was very old! Even in permafrost which is the ideal environment to preserve DNA this horse DNA was degraded quite extensively.
Contrast this to the 43,000 year old fossil horse which Mitchell does not mention in her article. This horse was also sequenced as part of the same study as the 500,000 year old horse and it was obtained from bones that were not preserved under ideal conditions and yet the DNA was in far better shape! So the fossil estimated to be much older had DNA that was much much more degraded just as expected/predicted by those who assume an ancient earth. However, in the YEC model these two sub-fossils (not completely fossilized technically) were found in sediments that young earth creationists would have to believe were laid down immediately after the flood and probably within just a few years of one another. If this is the case why does the one that is preserved in the best conditions have the worst DNA and why is the DNA really all that decayed at all. There are thousands of fossils that are from bones preserved during the most recent Ice Age that YECs would believe are from a time just after the Flood. These fossils have DNA that is in very good condition and easily sequenced. Why do these bones not have highly degraded DNA? According to AIG dinosaurs died during Noah’s Flood just 4300 years ago why is DNA not found in abundance in them when they were quickly preserved just a few hundred years before these horse fossils. YECs have provided no explanation/mechanism to explain why DNA is not found in all or most fossils.
There are large inconsistencies in the stories that AIG is telling its audience about DNA and its implications. Charitably, I don’t think they even think about the ramifications of their own claims when they are trying to discredit mainstream science but they should consider how their claims would affect their own hypotheses. If they did they might see that what they are saying is mostly nonsensical.
Ludovic Orlando, et al. Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse. Nature499,74–78(04 July 2013) doi:10.1038/nature1232