Thursday, 21 May 2015

Old Dog Teaches Science New Tricks

Ancient DNA suggests dogs split from wolves 40,000 years ago - life - 21 May 2015 - New Scientist

Here we have a very nice example illustrating why science gets it mostly right most of the time in contrast to religions which, if it ever gets anything right, it gets it right by accident. This is something that people like creationists and religious fundamentalists who seek certainty in everything, above even truth, find confusing. They seem to confuse certainty with knowledge and uncertainty with not knowing.

For these people, religion has obvious attractions and science is dismissed as worthless. What's the point of only thinking you know something when with religion you can claim to know everything with comforting certainty? God did it! As we say, religion is unreasonable certainty; science is reasonable uncertainty.

As I reported just last month in How Wolves Evolved Into Dogs, despite almost universal agreement that the domestic dog is a subspecies at best of the wolf (Lupus canis) and growing concensus about exactly how wolves evolved into domestic dogs, there was still no concensus about where and especially when this occurred.

The best estimates are based on an assumed genetic clock. This is the rate at which certain key parts of the genome are believed to mutate so, by counting the differences in these key areas between two populations or related species, it is possible to estimate how many years ago the two populations split. This method appeared to give a likely date of between 11,000 and 16,000 years ago.

But, and this is something that everyone working in this field or having an interest in it will realise, this all depends on getting the genetic clock right in the first place. For this reason no one in this particular field would ever claim with certainty that dogs and wolves split 'x' thousand years ago. Moreover, additional uncertainty comes from the fact that the genetic clock and the known archaeology seem to disagree. The evidence of changes in skull morphology from the available archaeology suggest a much earlier divergence at about 35,000 years ago.

Now, an examination of the DNA recovered from an extinct wolf that lived in Taimyr, northern Russia, 35,000 years ago by a team led by Love Dalén of the Swedish Museum of Natural History, Stockholm, has enabled the wolf/dog genetic clock to be recalibrated. It seems very likely now that wolves split into two lineages, one of which was the ancestor of domestic dogs between 27,000 and 40,000 years ago - entirely in line with the archaeology. They also showed that some northern varieties of dog interbreed with the Taimyr wolf so probably acquiring adaptation to a cold northern climate. These varieties include the husky.

  • An ancient Siberian wolf yields a first draft genome sequence of a Pleistocene carnivore
  • The 35,000-year-old wolf genome allowed recalibration of the lupine mutation rate
  • Dog ancestors diverged from modern wolf ancestors at least 27,000 years ago
  • Ancient Siberian wolves contributed to the ancestry of high-latitude dog breeds

The origin of domestic dogs is poorly understood, with suggested evidence of dog-like features in fossils that predate the Last Glacial Maximum conflicting with genetic estimates of a more recent divergence between dogs and worldwide wolf populations. Here, we present a draft genome sequence from a 35,000-year-old wolf from the Taimyr Peninsula in northern Siberia. We find that this individual belonged to a population that diverged from the common ancestor of present-day wolves and dogs very close in time to the appearance of the domestic dog lineage. We use the directly dated ancient wolf genome to recalibrate the molecular timescale of wolves and dogs and find that the mutation rate is substantially slower than assumed by most previous studies, suggesting that the ancestors of dogs were separated from present-day wolves before the Last Glacial Maximum. We also find evidence of introgression from the archaic Taimyr wolf lineage into present-day dog breeds from northeast Siberia and Greenland, contributing between 1.4% and 27.3% of their ancestry. This demonstrates that the ancestry of present-day dogs is derived from multiple regional wolf populations.*

*© 2015 Elsevier Ltd.

Of course, this tells us nothing about the process of domestication or even when it began. All it tells us is that around that time two populations of wolves diverged genetically and one went on to become domestic dogs. The process of domestication could have started some time after this divergence or even before it. It does not tell us for sure that the process of domestication itself caused this divergence.

So, we now have a more precise tool in the genetic clock which has enabled us to bring the genetic and archaeological evidence into line, and we now know that even after the split between the domestic dog's ancestors and the other wolves there was still some interbreeding.

As we would expect, given the self-correcting nature of science and the way uncertainty and doubt drive the quest for more information and better understanding, that different strands such as genetics and archaeology should eventually converge is only to be expected. In fact, as more and better information is discovered we would know there was something amiss if different strands of evidence were diverging. The simple reason for this is that science homes in on a single truth no matter what the starting point.

Using scientific methodology has taken mankind from horse, wind and water power and a life which for most people was nasty, brutish, ignorant and short, to the modern world of the Internet, the iphone, CT Scans, modern medicines, air transport, motor cars and computers. Religious fundamentalists and creationists, in their search for certainty by scrutinising very old books, have yet to progress mankind morally, scientifically or technologically beyond the Bronze Age when their old books were written. They reckon this certainty gives them the edge of scientific methodology with all its self-doubt and willingness to admit to being wrong.

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