A few weeks ago there was a report of an entire horse genome that was sequenced from a fragment of a horse preserved in permafrost sediments buried in the Yukon region in Alaska. The fossil was estimated to be 500 thousand years or more old and thus this represented one the oldest DNA sequences yet produced. I have written a whole series of posts about the origins of horses and how the discussion of horse evolution has been a source of both angst and use of considerable ink among young earth creationists. I didn’t have much to say about this genome sequence even though I did find it every interesting but then Elizabeth Mitchell at Answers in Genesis recently commented on this news report. The title of her article is A horse is a horse, of course, of course. I wish she would have read my article of a similar title (A horse is a horse, unless of course it isn’t a horse) that I started my series with, as she seems to have completely missed much of the significance of the genome to the young earth genetics model that I detail in that series.
Preservation of DNA: Mitchell brings up the usual issues of DNA preservation and supposed expectations that DNA should not be able to survive as long as it said to have existed in this horse tooth. But as I have said before, even if this were a problem for old-earth biology, and it doesn’t appear to be, this ancient DNA should be very perplexing to Mitchell’s views as well. If the world is so young why then is DNA not found in abundance in all fossil teeth. Rather than abundant in fossils, DNA is very difficult to find intact and having read the paper on this ancient horse genome the DNA 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 one was also sequenced as part of the same study 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 much older had DNA that was much much more degraded just as expected/predicted by models based on an old 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 many fossils that are from ice-age period bones that YEC would believe are from just after the Flood that 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 to explanation/mechanism to explain why DNA is not found in all or most fossils. There are huge inconsistencies in the stories that AIG is telling its audience about DNA and its implications. Really, 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.
This horse is a horse and was a horse long ago: What is more relevant to my past discussion of horses is that the genetic variation in horses is far too great to fit the simple explanation that Mitchell and AIG in general. The following quote regarding horse evolution from George Purdom, AIG’s resident geneticist, 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.
So here we have more confirmation that AIG’s current thinking is that all horses (donkeys, asses, zebras, domestic horses and wild horses) are all the evolved 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 three. Purdom calls this genetic sorting of raw material. Sow 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 recent study of genome sequence provides us with some clues about how long the different horse species have been distinguishable as horse lineages. Looking at the figures I have included you can see that the Thistle Creek ( the permafrost fossil sample) is more different genetically (ie. more DNA differences) than all the other horses though it is still clearly more of a horse than anything else the Donkey is still very different than these ancient horses. Just like domestic dog breeds which are found in early times, horses that are like today’s horses has been around as long as modern man has.
While this might sound like something that creationists want to be able to say, this is really not a help. If a horse has been a horse for thousands of years how can creationists claim that horses have a common ancestor with donkey’s, zebras etc… just a short time ago? The second figures 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 and 34,000 year old bone show sequences that are significantly divergent from all other horses. Many horse bones from sites dated more than 5000 years old still have sequences that are comparable to living horses. The creationists hypothesis of rapid divergence over 4000 years would predict archaeological sites they date as being right after the flood and thus the “oldest” should be far more divergent than are observed. Instead these results are perfectly consistent with predictions of how rates of genetic change over hundreds of thousands of years. 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 his rapid divergence has actually occurred in the last 4000 years.
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/nature12323