Saturday 25 August 2012

Buzz Off! Can't You See I'm Up to My Ears in the Organic Chemistry of El Sidrón's Dental Calculus???

Hmmm. I've been struggling with Stephen Bradley's comments on my recent post about Neanderthal oral hygiene at El Sidrón. Throughout he has maintained that the most likely source for the chemical constituents revealed by sophisticated mass spectrometry is wood smoke and cooked food. I have tried to suggest alternative natural sources of some of the compounds that he and his co-authors have identified.
     I would be dead in the water after his protracted comments on my earlier efforts were it not for my determination both to overcome my substantial ignorance of organic chemistry and to extend my argument beyond Stephen's assertions and, indeed, his conclusions. I'm having some success, I think. Take, for example, his insistence that alkenes and alkanes are plant waxes: 
The thermal desorption-GC-MS (TIC) (Fig. 1 inset) is dominated by a series of n-alkanes (carbon numbers C22 to C35), suggesting a higher plant source (Eglinton et al. 1962), most probably derived from plant waxes in the original food consumed.
I'll ask Stephen or some other organic chemist to adjudicate whether or not I've discovered another natural source of these chemicals--insects. Here is a snippet regarding the Dufour gland of a wasp, Habrobracon hebetor (Say) (Hymenoptera: Braconidae). 
The hydrocarbons consist of a homologous series of n-alkanes (n-C21 to n-C31), a trace amount of 3-methyl C23, a homologous series of internally methyl-branched alkanes (11-methyl C23 to 13-methyl C35), one dimethylalkane (13,17-dimethyl C33), a homologous series of monoenes (C(25:1) to C(37:1)) with the double bonds located at Delta9, Delta13 and Delta15 for alkenes of carbon number 25 to 31 and at Delta13 and Delta15 for carbon numbers 33 to 37 and three homologous dienes in very low amounts with carbon numbers of 31, 32, and 33. [emphasis added]*
I realize that eating insects isn't as sexy as eating cooked plants, specially not wasps. But it's not just wasps. A quick check suggests that hydrocarbons of all kinds are naturally occurring substances in insects. And it wouldn't be the first time that a primate was 'caught' eating insects. I've eaten crickets many times at sushi bars.
     I don't think I'll continue in this vein, trying to ferret out alternatives to Hardy et al.'s inferences. At this point I'd just like to chill on my veranda with a cold one.
     But not quite yet. This business with the El Sidrón Neanderthals' dental calculus has made me think about the assumptions that Stephen Bradley owned up to--that as far as he knows the Neanderthals made fires and cooked food and did numerous other things that you and I might do. I think otherwise.
     I don't know which is worse: me, having lived with the Middle Palaeolithic archaeological record for going-on 30 years and spending all my time trying to pierce the inferential balloons that my colleagues set free to ascend to the scholarly firmament, or earnest peers like Stephen Buckley having taken breath from those same balloons as a matter of course in their intellectual upbringing, spending all their time inadvertently adding to the cloud of colourful spheres floating above our heads. Whadda you think? I know what I think. I think this calls for me to touch on a subject near and dear to my heart in the near future--the context of discovery versus the context of justification (or verification). I've often been accused of being 'unscientific' because I start from the assumption that the Neanderthals were dummkopfs. So, stay tuned.
Arch Insect Biochem Physiol. 2003 Nov;54(3):95-109. Novel diterpenoids and hydrocarbons in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae). Howard RW, Baker JE, Morgan ED.

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  1. You have undoubtedly discovered another source of hydrocarbons – insects. It is well known that insects produce a huge range and complexity of hydrocarbons – alkanes and alkenes. However, they are usually accompanied by branched alkanes and alkenes too – you actually quote these in your piece. Plant wax esters, on the other hand, produce n-alkanes (and n-alkenes – these are often absent in archaeological samples, where they have undergone decay), with no appreciable branching (NOTE: alkanes, whether straight chain (‘n’) or branched, are highly – and equally – resistant to decay). We don’t see this branching, which is so typical of insects waxes (even wax of the house fly has been studied – perhaps people need to get out more!), in the dental calculus. Eating insects is certainly something we should consider; as you say, many modern humans have, and do. But the evidence from the El Sidron samples is consistent with plant waxes, rather than insect waxes. And we would still then have to explain the combustion markers – cooked insects?

    No, I (ME) don’t think that Neanderthals made fires, the chemical evidence strongly suggests that this is so. Given that other forms of complex behaviour have been attributed to Neanderthals in the past, as far back as the early 1970’s, certainly on the eastern side of ‘The Pond’, it would not be surprising to me IF it was so (I understand you choose not to believe any of the supposed evidence, of course). The VAST MAJORITY of the record of the human (and other hominids) past is invisible. What we pick up is only a small part of that. Consequently, the fact that we haven’t found something doesn’t not necessarily means it didn’t exist, it could simply be that we haven’t found it yet. It might NOT, but it could be.

    On a philosophical point, and nothing to do with what I consider to have been this constructive, questioning dialogue, I have noticed that in hominid studies it is inhabited by huge egos, more concerned with the agendas they want to pursue than with new science which may (only may) enlighten. To this extent, I find my work is perhaps somewhat of a distraction from the main focus, which is ego, rather than science, driven. To be fair, that can also be true of areas of archaeology and ancient history, where politics is often far more important than the archaeologically- and scientifically-based evidence; a good example of that being the ludicrous last decade in Egyptology where we have been asked to believe in fairies, albeit by an excellent teller of fairytales. As a scientist who feels no desire to pander to any given ‘sides’, I (perhaps unsurprisingly) find this very frustrating. Perhaps a less crudely politicised view of the world might one day emerge, but I’m not holding my breath! Thanks for being a rare listener Rob; it doesn’t necessarily matter whether we agreed, but that both listened. Stephen


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