Saturday 25 August 2012

The Paleo Diet and the Question of Cooking at El Sidrón Boils Down *cough* to n-alkanes. Who Could've Predicted?

Allright! Allright! I was wrong. The last words out of my mouth on this matter were that they would be my last words on the matter. Well, I was wrong. 
     I'm talking about the Neanderthal dental calculus chemical characterization undertaken by Stephen Buckley, and which was published under the title of 'Neanderthal Medics?' [catchy title] by Hardy et al. 2012. Certain organic compounds led the authors to infer that cooked vegetables were the source. Neanderthal chefs?
     Stephen was kind enough, and a responsible enough scientist [are you listening, all who're guilty of avoiding the Subversive Archaeologist?], to confront my suggestion that he and his colleagues may have overlooked some alternative sources for the organic compounds they found adhering to the El Sidrón Neanderthals' teeth [in the form of calculus--hardened plaque]. His comments on my previous attempts, herehere, and  here, are to be found by clicking here, here, and here. [It's all enormously edifying and entertaining. You should go.]  
     Today Stephen responded to what was to have been my last word, and in his characteristically mild and amicable way, he acknowledged that insects do indeed produce hydrocarbons. Then he said something odd. Even after I quoted from a scholarly paper that mentioned finding 'a homologous series of n-alkanes (n-C21 to n-C31) [graphically cited below],

Would I Lie to You? Click here for web access.

Stephen, maven of mass-gas chromato-stratigraphic-oscopy [or something equally unpronounceable and technically so far beyond my abilities as to be completely embarrassing ], states that insects are capable of producing hydrocarbons [well known to everyone else, it would seem, besides me], however 
'...[insects] 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)...' [comment on Buzz Off!]
'Bummer,' I said to myself. Another beautiful theory bapped in the face by a brutal fact. I was just about ready to slink off and back into the intertubes where I belong, when it hit me. Not the fact; the anomaly. Stephen was writing as if the species of parasitic wasp about which my article was talking contained only 'branching' alkanes. ]The anomaly, by the way, is that Stephen seemed to be making a rare slip.] 'What's up with that,' I asked myself. [Such protracted conversations with myself are occurring with frightening regularity, nowadays. Maybe I'm spending too much time alone. Ya think, Rob?] 
     So, I went to check. There they were. Branching alkanes. [Who'd've thought this archaeologist would one day find himself talking about branching organic molecules?] Undaunted [or so I'd want Stephen Buckley to believe] I soldiered on. And, my perseverance paid off. I wasn't imagining it! That pesky wasp was making n-alkanes, too. 'What a trooper,' I thought to myself [more concerned, this time, that I was personifying a wasp than that I was talking to myself again]. I have the proof right here. And, it's even more exciting than I thought it was the first time!
     Immediately below I'm reproducing the table showing the actual values, by weight, of each of the compounds that were found in the wasps' Dufour glands. BEFORE you go all weird about the size of the type, chill. The table is just for show. I'll extract the important data for you. But don't be surprised by the miniscule quantities reported. Wasps are small, mind you. So their little Dufour glands don't hold much of anything--according to this table, ~332 nanograms of organic compounds [that's billionths of a gram to the SI-challenged among you]. The truly gloatable bit from this table is that ~30% of the stuff in each gland should be sitting down, Stephen...n-alkanes. They run the gamut from n-C21 through n-C31. 30% by weight! Wriggle out of that one, Mr. biochemically savvy El Sidrón dental calculus man! 
Not bad, eh? Perhaps those El Sidrón Neanderthals weren't eating cooked plants after all. [crickets chirping]
     Moving on. Even if the vegetable-cooking inference of Hardy et al. falls flat on its face when faced confronted by the alternative, my efforts haven't made so much as a dent in their other major conclusion--that the Neanderthals were inhaling a lot of wood smoke. Gimme a break! I'm workin' on it. Let's see... Those Neanderthals prolly expired from smoke inhalation while huddling in their cave until the palaeo-firestorm was over, only the cave just concentrated the smoke and bits of it got stuck to the teeth of the Neanderthals, who were by think time gasping, mouths agape, for the last nanogram of breatheable air... [Hey, I'm allowed to make up stuff, too! Ain't I?]
     I'd like to acknowledge the patience and persistence that you're demonstrating, Stephen, in this protracted conversation with a total know-nothing-about-organic-chemistry type. Thanks. As for the other stuff--philosophy and absent evidence and all that--maybe some day soon we can sit down over a pint No! a Pimms No. 1 Cup in the back garden at the Wheat Sheaf in Oxford. That'd be perfect. Later.

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  1. Er..., I've no wish to wriggle out of anything, but you are right Rob, that insect waxes contain significant amounts of n-alkanes - 30% in the case you cite, as you say. The 'problem' is the fact that this same wax (and typical of insect waxes) is also accompanied by 31% of branched alkanes, according to the table (so about the same). IF it was an insect wax in the dental calculus of the El Sidron Neanderthals then we would also expect to see significant amounts of branched alkanes TOO. The fact that branched alkanes are absent and we ONLY see n-alkanes IS typical of 'boring' plant waxes, but NOT the 'crazier' insect waxes, where their chemistry is much more interesting (well to me, anyway...!). One could try to suggest that the branched alkanes degrade much more easily compared to the n-alkanes, so it could still be an [albeit degraded] insect wax. Unfortunately, that's not the case; they degrade at a similar rate and are normally fairly resistant to decay (this 'diagenesis' is a key part of our approach).

    IF this wasn't about Neanderthal diet there would be a general agreement between the scientists on 'plant'. But of course it is! I would say that scientists like myself SHOULD be questioned about our results, rather than be seen as 'all-knowing beings' [we're NOT!], and people swallowing the science whole - this DOES happen far too often. We find true understanding by asking 'why?', NOT by looking at how big the name is and deciding whether to 'trust it'. In this respect, I'd like to thank Rob for questioning the science. Science can be powerful, but it is certainly not infallible, and nor does it have all the answers. In my PhD thesis (some time ago now) I had a quote I felt was apt - 'Believe those who are seeking the truth; doubt those who find it.' (Andre Gide). Indeed!

    I'm not sure about the Pimms, but I'd be happy to discuss the wider significance at the Wheat Sheaf in Oxford, one day... S

  2. I confess I’m beginning to find our conversation a bit frustrating, SB. By the way, all those comments about you wriggling, being a maven and so on are meant to be good-humoured teasing. In anthropology it would be considered a sign of what’s called a ‘joking relationship,’ which itself indicates a good-natured cameraderie. I hope I wasn’t being too presumptuous in defaulting to such jests, given that we’ve never actually met!

    As for the frustration. I’m feeling a little like a mushroom. By that I mean I feel as if I’m being kept in the dark, with the only light the occasional visit by the farmer to nourish me with something that most would consider less-than palatable. ;-)

    Let me explain using your latest comment, in response to which I’m writing at the moment. In your paper you publish reconstructed total ion chromatograms, and not the original data, as is the case with the Howard, et al. paper on insect paraffins. Compounding my confusion is the way in which you've chosen to report on what’s revealed by your analyses. In your Fig. 1, for example, you name a few unique compounds, while referring to others by their group names, such as alkanes. In your supplementary material you publish a table, which you freely admit is selective. ‘We have given likely credible sources based on the chemistry and botanical and archaeological context; we do not suggest this list is exhaustive.’ I could find nowhere in your paper where you state that branching alkanes were totally absent. My latest blog post was predicated on your earlier statement that, while insects ‘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.’ I had another look and saw that the insect paraffin contained heaps of n-alkanes. As a reader of your paper and of the supplementary material, and like most of your readers in no way an expert on plant and insect paraffins, how was I to know that your samples contained NO branching alkanes? I hope you can understand why I find this frustrating, at the same time that, I fear, you’ll be finding this quite tedious.

    In this, perhaps my last gasp in the life of this conversation, I would like to comment on your statement that both types of alkane degrade at a similar rate (and my recent research reveals that the branching form are slightly less susceptible to biodegradation than their straight counterparts). However, that same research has discovered that branching alkanes are highly susceptible to fragmentation.’ And, although you don’t refer to this process in your paper, the insect paper than I’ve been referring to, in stating the methods, makes this statement, which I find interesting only because it relates to a process that for all I know could result in differential visibility of straight and branching alkanes. Here is what the insect people say: ‘Hydrocarbon components were identified from their characteristic EI-MS fragmentation patterns..[references]…in conjunction with equivalent chain length values.’ I must show my gross ignorance, once again, but I must ask you if this was a standard step that your analyses included, and as such you saw no need to report. Or, is there something special in what Howard et al. did, perhaps to reveal the fragments of branching alkanes that would otherwise have been invisible?
    I’m sorry to have to be such a bother, SB. It’s not that I don’t trust you, or think that you’re being in any way disingenuous; I simply need to know for my own peace of mind.

    By the way, I’m choosing not to erect another blog post with these additional comments, to spare you the need to respond simply because I’ve broadcast my labyrinthine thoughts to the e-world. Nor am I concerned that I might look like a complete ninny if I were to have posted this on my blog. No, I’ll be quite happy just to hear what you think right here on LinkedIn. Thanks for being such a sport! RG

  3. It's the veggies that make you healthy!

    The Paleo Diet Is Uncivilized (And Unhealthy and Untrue).

    Seven Reasons Why We Have NOT ‘Evolved’ to Eat Meat


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