Isotopes and red herrings: comments on Milner et al. and Liden et al.

Isotopes and red herrings: comments on Milner et al. and Liden et al. These comments are primarily in response to the paper by Milner etal. who argue in favour of a far less clear cut interpretation of thebody of isotopic data of human bone collagen isotopic composition at theMesolithic--Neolithic transition, and, if applying the interpretationaccording to according toprep.1. As stated or indicated by; on the authority of: according to historians.2. In keeping with: according to instructions.3. current assumptions, to give more cautious generalisationsabout the main dietary sources. The argument is driven by perceiveddiscrepancies between estimating the major dietary resource fromisotopic evidence and from field excavation data. However, it is difficult to document the discrepancies unless thedifferent kinds of evidence are available in the same place. Forexample, where Neolithic shell mounds and/or evidence for fishing arevery clear, there are virtually no human isotopic data available thatconflicts with. a marine dietary resource. Furthermore it is not at allclear how one might assess the contribution of marine resources (definedas fraction of dietary protein, for the sake of argument) from suchevidence as the quantity of surviving fish bones, or shells in mounds.Moreover, Milner et al's argument is based most strongly on thesituation around the Baltic and North Sea, while the isotopic evidencethey discuss is from sites mainly in the western UK. However, thoseisotopic results could be expanded to include data from the ChannelIslands, Brittany and the W coast of France, arguably ar��gu��a��ble?adj.1. Open to argument: an arguable question, still unresolved.2. That can be argued plausibly; defensible in argument: three arguable points of law. the coast ofPortugal, and in fact the same picture is also applicable to thoseNeolithic sites studied in the Mediterranean e.g. (Richards et al. 2001;Papathanasiou 2003). My main purpose, however, is to reflect on the interpretation ofthe isotopic evidence from human bone. Part of the argument of Milner etal is based on there being too few human individual results from whichto generalise with certainty. This can only be countered at a verydetailed level--but the fact is that scores of human Neolithic bonesfrom dozens of coastal sites over a very wide range of Europeancoastline contain, without exception, terrestrial-value isotopiccollagen. It is quite safe to assert that Mesolithic human bonefrequently exhibits collagen isotopic composition enriched in [sup.13]Ccompared to accepted terrestrial values, which can be interpreted, asexplained by Milner et al, as due to the consumption of between 25 and90 per cent protein--depending on the value measured but often in thehigher range--from marine sources. In contrast, all Neolithic--periodhuman bone so far measured, from coastal sites, although comparativelyuncommon, exhibits collagen isotopic composition which does notsignificantly differ from terrestrial values. There is no dispute in Milner et al concerning results whichexhibit high marine resources. The problem really arises for thesituation where, on non-isotopic evidence, significant marine protein isapparently consumed, but is not registered as a detectable enrichment of[delta][sup.13]C in human bone collagen, and it is this point which isthe crux of the matter Noun 1. crux of the matter - the most important pointcruxalpha and omega - the basic meaning of something; the crucial partpoint - a brief version of the essential meaning of something; "get to the point"; "he missed the point of the joke"; "life . There are four main issues that bear on the interpretation ofpartial marine diets: 1. How well the terrestrial "end point" can be defined(in terms of [delta][sup.13]C values). Put very roughly, a change of 1[per thousand] corresponds to about 10 per cent change in marine intake.If the terrestrial end-point is uncertain to [+ or -] 1 [per thousand],this allows a difference of about 20 per cent in deciding what is aminimum detectable level of marine consumption. This is likely to be aworst case--but points up the need to present relevant data and considerthe errors involved, when aiming for quantitative statements at dietswith a minor marine component. 2. Variation in the enrichment of [sup.13]C in food chains. Milneret al present data which show that estuarine es��tu��a��rine?adj.1. Of, relating to, or found in an estuary.2. Geology Formed or deposited in an estuary.Adj. 1. estuarine - of or relating to or found in estuariesestuarial foodchains are liable to beless enriched than offshore and/or high energy littoral littoral/lit��to��ral/ (lit��ah-r'l) pertaining to the shore of a large body of water. littoralpertaining to the shore. environments.This could apply to molluscs, crustacea and detritivorous fish. This maywell apply in specific cases, but could not do so on the rocky shores ofthe Atlantic coast. It is certainly a point to be investigated further,but can hardly be used as a general argument for re-interpreting theoverall picture. 3. Radical re-interpretations of collagen isotopic composition.There is very little room for manoeuvre here (and none is suggested byMilner et al). The general interpretation ("you are what youeat", etc) is so well supported in so many different scenarios asto be unassailable, even if real limitations in our knowledge remain.One such is knowing how well collagen registers the average orintegrated diet. Most bone collagen is laid down during adolescence, andthen remodelled throughout later life. So, for example, fish eaten onlyin adult life may nor be fully represented (remodelling rates especiallyfor compact bone are not at all well known). Nor can we be sure aboutthe representation of fish eaten seasonally, or perhaps in theoccasional feast--although these effects are likely to be small. A glut glutpronounced as rut, slut Vox populi An excess of a service or skilled labor in a particular area. See Physician glut. might lead to higher representation in stimulating turnover, and inconstituting a high protein diet; although the acidotic ac��i��do��sis?n.An abnormal increase in the acidity of the body's fluids, caused either by accumulation of acids or by depletion of bicarbonates.ac (and potentiallybone resorptive) effects of a high protein diet have also been cited(Parkington 1991). 4. Does collagen represent dietary protein or dietary total carbon?This simple question (also raised in Milner et al) does not (yet) have asatisfactory answer. The point is recognised to be a major issue inpalaeodietary reconstruction, and these remarks are a very briefsummary. At high protein intakes the consensus is that, for humans,collagen represents mainly dietary protein. The issue is lessstraightforward at low protein intakes, and might also be furthercomplicated by "low quality" protein intake, in which theamino acid amino acid(əmē`nō), any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins. balance from plant-derived protein leads to relativelygreater immediate amino acid catabolism. There is no fundamentalmetabolic reason why dietary carbohydrate cannot be used to synthesize To create a whole or complete unit from parts or components. See synthesis. the non-essential (dispensible) amino acids, and this can be seen infeeding experiments on pigs, (whose metabolism is not so far fromhumans) where analysis of individual amino acids shows a clear but notovelwhelming contribution of carbohydrate to bone collagen in severalamino acids (Howland et al. 2003). Therefore the proposition has to betaken seriously. The effect of protein versus whole diet representations may beexplored in the following scenario. Consider four human groups consuming four different diets, namelyhigh and low protein, and either all-terrestrial food or where 20 percent of protein is from a marine source. Consider also that each group could be synthesizing collagenaccording to one of two extremes. Either where only dietary protein isrepresented (the "protein routing" extreme); or alternativelywhere all digested carbon is equally represented (the"scrambling" extreme). We now evaluate the expected collagen [delta][sup.13]C for alleight cases. For this we need to define suitable [delta] values for thefoodstuffs foodstuffsnpl → comestibles mplfoodstuffsnpl → denr��es fpl alimentairesfoodstuffsfood npl → , and the degree of isotopic fractionation fractionation/frac��tion��a��tion/ (frak?shun-a��shun)1. in radiology, division of the total dose of radiation into small doses administered at intervals.2. in converting afoodstuff to collagen. This scenario is easily modelled as a spreadsheet and readers might like to verify that the main feature of theoutcome does not depend on any particular choice of values from within areasonable range. The interesting point is to note the change in [delta] between theterrestrial and 20 per cent marine situations. This is 1.8 [perthousand] for direct routing, whether or not the diet is a high or lowprotein one. A similar value, of 1.3 [per thousand], is achieved for thescrambled routing, for a high protein diet. However, a scrambled lowprotein diet shows five times less difference, i.e. only 0.34 [perthousand]. These are admittedly extreme cases--although such high andlow protein quantities can be found in contemporary human diets. Thetypes of protein routing are no doubt also exaggerated. The importantpoint is that this model shows that a low protein diet (where scramblingis most likely) may not be as sensitive to a minor quantity (i.e. 20-30per cent) of marine protein, as is implied in the simple linear model(exemplified in the high protein or in the direct routing scenarios).These are models only-there is no decisive evidence for what actuallyhappens. But a low protein diet is probably significantly lessisotopically sensitive to a small percentage level of marine proteinthan the straightforward linear interpolation Linear interpolation is a method of curve fitting using linear polynomials. It is heavily employed in mathematics (particularly numerical analysis), and numerous applications including computer graphics. It is a simple form of interpolation. implies. Conclusion and summary I am not convinced that there is a conflict between any of theisotopic results, as standardly interpreted, and the archaeologicalevidence. In any case, the isotopic results under discussion, at anylevel of interpretation, show marked changes in their average valuesbetween Mesolithic and Neolithic skeletons in Britain (Richards et al2003) and along the NW Atlantic generally, and this remains the strikingfeature of the data. It is in keeping with the drastic changes incultural assemblages, and also in the distribution of human presence, inthe Neolithic. However, the change in geographical distribution the natural arrangements of animals and plants in particular regions or districts.See under Distribution.See also: Distribution Geographic of theskeletal evidence potentially invites a circular argument, and if theissue is to be discussed as a general whole, the approach needssubtlety. Once the transition is examined closely, and we demand to knowexactly how important marine resources were for the Neolithic humans whomight have benefitted from the sea's resources, the absence of amarine signal in bone collagen carbon isotopes may not be suchincontrovertible evidence incontrovertible evidencen. evidence introduced to prove a fact in a trial which is so conclusive, that by no stretch of the imagination can there be any other truth as to that matter. for absence of a partially marine diet. Thatis, we cannot, on current understanding, rule out that the level ofmarine resource consumption which is indistinguishable from terrestrialvalues from a bulk collagen measurement may, under some conceivablecircumstance, be as high as 30 per cent. This possibility brings someinteresting archaeological science Archaeological science (also known as Archaeometry) is the application of scientific techniques and methodologies to archaeology.Archaeological science can be divided into the following areas: into play, and the issue requiresmore research before it can be resolved. Additional evidence, forexample from relevant analyses comparing essential and non-essentialamino acids, would help throw light on this.Diet Compositions Considered Terrestrial 20% marine high highWeight (g/day) protein proteinTerrestrial animal protein 180 140Marine protein 0 40Plant protein 20 20Terrestrial animal fat 90 72marine fat 0 18plant fat 5 5plant carbohydrate 100 100Total calories 2105 2105Total protein (g/day) 200 200% Protein as marine 0 20 terrestrial low 20% marineWeight (g/day) protein low proteinTerrestrial animal protein 30 18Marine protein 0 12Plant protein 30 30Terrestrial animal fat 10 6marine fat 0 4plant fat 10 10plant carbohydrate 400 400Total calories 2220 2220Total protein (g/day) 60 60% Protein as marine 0 20Isotopic Values Used change in delta delta ([per ([per thousand]) thousand])Terrestrial animal protein -24Marine protein -15Plant protein -25Terrestrial animal fat -29marine fat -21plant fat -30plant carbohydrate -26enrichment to collagen 4.5Outcome Collagen delta Collagen ([per delta thousand]) ([per direct thousand])Diet routing scrambledHigh protein, terrestrial -19.6 -21.9High protein, 20% marine -17.8 -20.5Low protein, terrestrial -20 -21.6Low protein, 20% marine -18.2 -21.2 (1) Research Laboratory for Archaeology, 6 Keble Road Keble Road is a short road running east-west in Oxford, England. To the west is the southern end of the Banbury Road with St Giles' Church opposite. To the east is Parks Road with the University Parks opposite. Blackhall Road leads off the road to the south near the western end. . Oxford, UK Received: 21 October 2003; Accepted: 3 November 2003 References HOWLAND, M. R., L. T CORR CORRUsed on the consolidated tape to indicate a correction in a reported transaction : CORR.LAST.GY 50 WAS 51. , S. M. M. YOUNG, V. JONES, S. JIM JimMiss Watson’s runaway slave; Huck’s traveling companion. [Am. Lit.: Huckleberry Finn]See : Escape , N. J.VAN DER DER - Distinguished Encoding Rules MERWE, et al. 2003. Expression of the dietary isotope signal inthe compound-specific [delta][sup.13]C values of pig bone lipids andamino acids. International Journal of Osteoarchaeology 13:54-65 PAPATHANASIOU, A. 2003. 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