Pyrene, Good Night, Pyrene…With Apologies to the Immortal Lead Belly

Huddie William Ledbetter (January 20, 1888 – December 6, 1949)

[Update: Stephen Buckley continues his riposte in the Comments. Just click on the link at the foot of this post. 2012.08.21]

The other day I wrote about fact-checking Hardy et al.‘s recent treatise ‘Neanderthal Medics?‘ I pointed out that there was no substantive reason to accept their claim that the presence of four carbon compounds–flourene, fluoranthene, pyrene and phenanthene–implied that the El Sidrón Neanderthals had inhaled wood smoke. 
     Tonight I’d like to take up another of their conclusions, that several other chemical compounds indicated the presence, in dental calculus, of bitumen or oil shale. I should remind you that dental calculus largely comprises dead oral bacteria. As the authors put it

Also identified were a series of hopanes (carbon numbers C29 to C33), indicative of an oil shale or bitumen and corroborated by the presence of the isoprenoid hydrocarbon biomarkers phytane and pristane … (p. 620)

Hopanes? Hopanoids. According to my favorite encyclopaedia, Wiki, the main function of hopanoids ‘is to improve plasma membrane strength and rigidity in bacteria.’ Hmm. Bacteria. Arrrr, Jim. Bacteria be the creaturs that make the biofilm that forms dental plaque, first off, and then calculus. Arrrr. It may well be the case that hopanes occur in bitumen or oil shale, but that may well be because both substances are the end-product of organic decomposition, decomposition that would in all likelihood have involved bacteria and other microorganisms. 
     ‘Pristane is a natural saturated terpenoid alkane obtained primarily from shark liver oil, from which its name is derived (Latin pristis, “shark”). … It is also found in mineral oil and some foods. Biosynthetically, pristane is derived from phytol.’ Among other sources of phytol, ‘… [i]n ruminants, the gut fermentation of ingested plant materials liberates phytol, a constituent of chlorophyll, which is then converted to phytanic acid and stored in fats.’ Phytane is a diterpenoid alkane that’s formed by the breakdown of phytol. 
     Granted, as Hardy et al. mention, these are all products that might be found in bitumen or oil shale. But, as I’ve pointed out, there’s nothing unambiguous about the source of these compounds in the Neanderthal dental calculus at El Sidrón. And, for all we know, the (stable isotopically characterized) carnivorous Neanderthals, along with the meat and connective tissue, were consuming the contents of the rumen of their prey, much in the way the !Kung men on the hunt once did as a way of acquiring water where none occurred on the landscape.
     I find it really hard to believe that the editors of Naturwissenschaften gave more than a second’s thought to the authors’ interpretations, so taken must they have been by the study’s results. After all, it’s not every day that you get to see a report based on sequential thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), such as that of Hardy et al. Only problem is, when an archaeologist fails to rule out natural occurrences before imputing Neanderthal behaviour, it’s like popcorn without butter. It’s indigestible.
     For my part, I’ll go back to imagining the Neanderthals occasionally inhaling the smoke of wildfires, and waiting for extinction while they fed on whatever they could of the animals they brought down or scavenged.
     Do I really need to go on in this manner? Or, have I satisfactorily demonstrated the wrong-headedness of Hardy et al. I don’t see the point. Anyone care to take the wheel?
    

     

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2 thoughts on “Pyrene, Good Night, Pyrene…With Apologies to the Immortal Lead Belly

  1. Hi Rob,

    I think it’s useful to quote you here:

    ‘Their inference here – that the Neanderthals were inhaling smoke – depends ENTIRELY on the erroneous claim that the four compounds are present in the Neanderthal’s dental calculus because of smoke inhalation. I have to ask, ‘How likely is it that a group of Neanderthals inhaled smoke from charcoal production or salmon smoking in a reducing environment, tobacco smoke, vehicle exhaust or hazardous waste?’’

    To answer the first part, it does NOT depend ENTIRELY on the four compounds, as I made clear in my posts. To answer the second part, well it’s not at all likely, in fact, the suggestion is silly, as Rob rightly implies. Perhaps a point of clarification is useful here; inhalation or ingestion are the two possible routes.

    To quote Rob again:

    ‘The authors have done NOTHING, not a thing, to rule out the natural sources of the chemicals they report on.’

    Well actually, ensuring that the biomolecules identified came from INSIDE the mineral-based calculus goes quite some way, so let’s go through the possibilities:

    Suggested alternative sources:

    Tobacco smoke – despite the possibility that they may have been a little more advanced than we previously supposed, it seems unlikely that Neanderthals smoked tobacco (even if it was indigenous to Spain, rather than the Americas).

    Coal-burning appliances/coal – again, I don’t think Neanderthals would have exploited coal in this way.

    Coal tar asphalt: unlikely that they were heating this – I agree with Rob here.

    Vehicle exhausts: Neanderthals didn’t drive, as far as we are aware.

    Agricultural burning: I don’t think anyone is suggesting that Neanderthals invented farming, with, or without, purposeful burning.

    Hazardous waste sites: these are a recent human ‘development’ so Neanderthal s having and using them seems unlikely.

    Wildfires: a possibility (the first), perhaps, but to see the quantity we see in dental calculus it would suggest these were common events and Neanderthals were exposed to very significant amounts of smoke from these regular wildfires.

    An alternative hypothesis:

    1. Acyl lipids: the presence of cooked plant material (from plant oil, so NOT from wildfires)
    2. Alkyl phenols: the presence of wood smoke/wood smoked foods (+ wildfires), or formation of gas, coal or oil
    3. PAH’s (pyrene, etc): combustion markers: e.g. wood fires (+ wildfires), cooked food, or volcanoes, formation of gas, coal or oil

    These three disparate chemical groups are collectively consistent with the smoking or roasting of plants (and animals) for food. This can be combined with it being highly unlikely that the Neanderthals were exposed to enough wildfires for the amount of PAH’s (pyrene, fluorathene, fluorene and phenanthrene (and others)) to show up at all in the dental calculus, rather than these airborne molecules being inhaled into the lungs, as would be most likely (these play a huge part in lung cancer). In contrast, regular INGESTION of cooked (‘burnt’) food – chewing with teeth – would seem the most likely reason for finding these molecules WITHIN the dental calculus of these individuals. They would be part of the consumed food – compare to well-done/burnt toast, which also contains PAHs. Inhalation of smoke from regular fires could perhaps do similar if the individual was often in close proximity, but ingestion perhaps makes most sense (although I’m not the archaeologist/anthropologist!!). S

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  2. Part 2
    Sorry, but it’s worthy of comment:

    ‘According to my favorite encyclopaedia Wiki…’ – are you being ironic?? Wiki is full of absolute ‘no polite words’ – some are very good, but the quality is so variable, and the content often so politicised, that no one should allow students or children (or others) to use them as a primary sources, if they want them to be genuinely well educated (though they can be a useful starting point if one realises their major shortcomings). Sorry, but it’s – still (though better) – full of junk.

    Shark attack?

    Bacteria and other microorganisms are indeed believed, with good scientific justification, to be the original source of the hopanes (and steranes) present in natural petroleum sources such as bitumen (asphalt) and oil shales. The bacterial hopanoids are familiar to organic geochemists (my doctorate, which included organic geochemistry, was carried out in the University of Bristol’s Organic Geochemistry Unit), as are their resulting defunctionalised ‘biomarkers’ (essentially what they become as they degrade over time), the hopanes.

    But for some context: dental calculus samples from both humans and animals were analysed in this study (see ESM), and although it is perhaps reasonable to expect to observe bacterially-derived hopanoids, or their resulting biomarkers, the hopanes, these were not present in any of the samples analysed. Instead, the organic components were dominated by the food they consumed (see ESM). The bacterially-derived hopanoids do NOT disappear into thin air, to then reappear ‘Star Trek-style’ as hopanes, so it is reasonable to assume they at least might have come from a bitumen or oil shale/seep source (read on).

    On the pristine and phytane – and you can extend it to many, many, many compounds – you are right that there are other sources (as is often the case – what is important is the context):

    Unfortunately, the pristane and phytane was ONLY observed in the pyrolysis-GC-MS, which is typical of petroleum oil-based kerogen, i.e. these are bound up in the polymeric part of the natural petroleum product and only released when this bound fraction is broken apart by strong heating. More importantly, perhaps, this means that the pristane and phytane cannot derive from ingesting them from consuming rumen (though it’s a reasonable idea if one doesn’t know this), or any other part of their diet (e.g. shark!).

    I would be the first to say that bitumen or similar is very surprising, but the biomarker approach, which looks at ALL the biomolecules, not just one, would seem to point to bitumen/oil. Moreover, natural bitumen has been found on 70,000 BP Neanderthal stone tools from Syria (where there is no natural bitumen/oil) and was assumed – reasonably, but not conclusively, to have been used as hafting. The source of the natural bitumen on the stone tools was ~40km away. It the case of El Sidron the nearest source is ~15km, so feasible. Using their mouth (and teeth) as a tool would also be reasonable – no, that doesn’t make it so, although it might make it plausible.

    Speaking for myself, I would have liked to include more in the Naturwissenschaften paper, but we were limited by space in the print version. I would also say – typical scientist! – we need to do more research, but within the constraints of the study and the evidence currently available, the conclusions were reasonable, particularly given the seemingly even less likely alternatives! – cf. Sherlock Holmes quote (I note yours, Rob).

    A final point: In the UK/Europe the possibility that Neanderthals had what we might describe as modern human behaviour is not such a big deal. Books written by academics as far back as 1973 cite such evidence (I’m sure it can be – is!! – disputed). Perhaps this also says something…?

    Stephen

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