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Tuesday 2 October 2018

More on the strontium isotope "West Wales connection."

I forgot to mention that when I wrote to Christophe Snoeck about that famous (infamous?) paper published in early August, I did get quite a prompt reply not from Dr Snoeck but from Dr Rick Schulting from Oxford University.  So I have to thank him for that.

He addressed the points raised as follows:

1. I can see no evidence of any sort in your research which supports the contention that some of these individuals came from West Wales rather than any other part of Palaeozoic Britain. Have I missed something?

Apparently you have. "Those with the highest values (>0.7110) point to a region with considerably older and more radiogenic lithologies, which would include parts of southwest England (Devon) and Wales (parsimony making locations further afield – including parts of Scotland, Ireland and continental Europe – less probable).”

“While strontium isotope ratios on their own cannot distinguish between places with similar values, this connection suggests that west Wales is the most likely origin of at least some of these individuals…”

So we fully acknowledge that the Sr isotope results on their own are not sufficient to make a specific link with west Wales, and that this relies on accepting that the archaeological connection implied by the bluestones being transported by humans, which obviously you don't accept. That is a separate issue.

2. Why have you simply accepted Mike PP's contention that there are bluestone quarries in West Wales without acknowledging that there is a major dispute about the reliability of his evidence?

We chose not to enter into this debate in this paper, since it has been discussed elsewhere, and the format of this kind of paper is by its nature very brief.

3. Why have you marked Craig Rhosyfelin on Figure 2 when it has no relevance whatsoever for the data shown on the map?

It is marked as one of the proposed sources for some of the bluestones. It is also the location for some of the plant samples taken for the Sr baseline for this part of west Wales. So it has relevance for both points.

4. I can see no evidential basis for the "geographical assignments" chosen in Figure 3. The individuals chosen could just as well have come from a multitude of other places.

No, they could not have. The assignments shown on the map for the left-hand figure are the only locations in Britain that are consistent with the Sr isotope result for that particular individual (and you’ll note that the locations are not limited to west Wales), to the specified degree of confidence. These are based on spatial statistics using the most complete Sr baseline map currently available for Britain.

5. I'm not convinced by the "local" and "far travelled" designations either. Is there really any significance in your "cut-off point" of 0.7090?

"The strontium isotope ratios for modern plants clearly distinguish the Ordovician and Silurian lithologies of west Wales (0.7095–0.7120) from the Cretaceous chalk of Wessex (0.7074–0.7090), which extends for at least 15 km around Stonehenge in all directions."

The use of a 0.709 upper cut-off for the Cretaceous Chalk is if anything rather conservative, as no values this high on plants have been reported. We can and do support its significance using spatial statistics as reported in the paper and in supplementary information. A comparable range has been used in other strontium isotope studies in the Stonehenge region.

6. The isotope ratios for modern plant materials from West Wales -- why are there apparently no controls from other sites as well? This is another example of a strong -- and very unfortunate -- bias in the research.

This is inaccurate. We used the most up to date Sr baseline map available for Britain, from Evans et al. 2010 with additions. This provides the characterisation (‘controls’) for the rest of Britain shown in Figure 2, with the right hand side showing the corresponding uncertainty, which takes into account the lower sampling resolution of many parts of Britain. We specifically sampled and measured additional plants from west Wales to be able to characterise that area more thoroughly and thus better understand the range of variation there. We also provide new values from the Berkshire Downs to the north, bordering the Vale of the White Horse, obtained as part of another project, but again supporting the cut-off value of 0.7090 for the Chalk. 



Dr Schulting accepts here -- in several places -- that  there is no scientific basis for the assignment of one or more individuals to West Wales -- or more specifically to the area near Rhosyfelin.  Their thesis is based on the acceptance of the idea that there was an "archaeological connection" between Stonehenge and West Wales, involving the human transport of the bluestones.  The authors do not even discuss that idea -- they simply accept it to be true.  (Classic "assumptive research", to use the phrase of my old friend Prof Brian Roberts.)  That is in itself bad science, especially since the quarrying hypothesis, at both Rhosyfelin and Carn Goedog, is falsified by the radiocarbon dates obtained by the researchers themselves.   The authors of this Nature paper must have known that.  

I do not accept the line that Snoeck et al chose not to enter into that debate simply because it has "been discussed elsewhere".  Where has it been discussed elsewhere in the scientific literature?  Not in a single paper by MPP and his colleagues  -- they spend their time on promotion, not discussion.  Only two papers have discussed the quarrying theory -- and both of those (by Dyfed, John and me) show that the theory is fundamentally flawed.  Schulting and his colleagues have simply chosen to ignore our published work because it is inconvenient.

The choice of Rhosyfelin as a key location?  Again guided by MPP, without any questioning, and again demonstrating unacceptable bias in the work.

On point 4, could the individuals examined have come from multiple other locations?  Schulting says: ...The assignments shown on the map for the left-hand figure are the only locations in Britain that are consistent with the Sr isotope result for that particular individual (and you’ll note that the locations are not limited to west Wales), to the specified degree of confidence."   Notice the very careful wording!  What is bizarre in this case is the assumption that the individual in question lived a static life, and acquired the strontium signature by staying in the same place.  We know that people moved about -- indeed, this one (individual 288) ended up in Stonehenge!  The authors fail to recognize that he or she could have acquired the high value signature by moving from an even higher value signature area to an area with a lower signature -- or vice versa. The value is an average value, not a value that demonstrates a fixed place of residence.  So to talk about "statistical probability" or "high degrees of confidence" is -- with all due respect -- nonsensical.  It's like saying "It is statistically probable that there is a remote possibility that this is the case"...........

On the matter of the cut-off point between "local" and "far travelled" designations, Dr Schulting does not answer my point.  I don't care about spatial statistics and supplementary data sets --  nothing has been done in the work to show that the wood used in the cremations came from any further away than (for example) Frome or the Mendips.

On point 6, asking why there were no control site tests to justify the choice of Rhosyfelin and West Wales as the home patch of individual 288,  there is again no answer.  Additional samples taken on chalklands do not constitute proper controls to test the reliability or usefulness of the samples taken at Rhosyfelin.  Samples should have been taken from other areas OFF THE CHALK AND REMOTE FROM WEST WALES. 

As I noted before, this paper is so biased and unreliable that it should never have been published. 

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