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Posts Tagged critical thinking

oxygenated food for the brain? Alison Campbell Aug 18

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I was reading a couple about ‘raw foods’ today. This is ‘raw foods’ as in ‘foods that you don’t heat above 40oC in processing them.’ It’s also as in, a vegetarian diet. (I do rather enjoy vegetarian food & when we had a French exchange student staying with us that was pretty much all we ate, because that was what she ate & it must be hard enough being half a world away from home without having to live in a house of voracious carnivores. But I don’t think I could eat nothing but, all the time; I like meat too much.) Anyway, what caught my eye wasn’t so much the diet program itself but the mis-use of science to promote it. That did rather get my goat brocolli.

Apparently you should get your kids to eat their greens (along with the rest of the diet) by telling them that plants do this wonderful thing: they turn sunlight into chlorophyll & when you eat it – it will give you extra oxygen. Sigh… This concept was repeated in the second article, which told me that raw (but not cooked) foods are ‘oxygenated’ & thus better for your brain, which needs to be fully oxygenated to work properly. Well, yes, & so do all your other bits & pieces, & they don’t get the oxygen from food. As Ben Goldacre once said, even if chlorophyll were to survive the digestive process & make it through to the intestine, it needs light in order to photosynthesise, quite apart from the fact that you don’t normally absorb oxygen across the gut wall. And it’s kind of dark inside you :)

The second shaky claim related to digestive enzymes. Because raw foods are ‘alive’ then they are full of enzymes. And so we’re told that eating them will help you to digest your meals better.

Er, no. FIrst, because when said enzymes – being proteins - hit the low pH environment of your stomach they are highly likely to be denatured. This change in shape means that they lose the ability to function as they should, & in fact they’ll be chopped up into amino acids like any other protein in your food, before being absorbed & then used by your cells to make their own enzymes.

And second – the raw foods diet is plant-based. Yes, plants & animals are going to have some enzymes in common. I’d expect that those involved in cellular respiration & DNA replication/protein synthesis would be very similar, for example, because these are crucial processes in any cell’s life & any deviations in form & function are likely to be severely punished by natural selection. But we already have those enzymes; they’re manufactured in situ as required. In other words, even if the plant enzymes somehow made it into cells intact & capable of functioning, they’d be redundant. However, with a very few exceptions, plants aren’t in the habit of consuming other organisms so, in regard to plant cells being a good source of the digestive enzymes required to for the proper functioning of an omnivore’s gut – no, I don’t think so. No.

You might say, why on earth do you bother about this stuff? After all, it’s not doing any harm. But the thing is – science is so cool, so exciting; it tells us so much about the world – why do people have to prostitute it in this way? Kids (& others) are fascinated by the way their bodies’ organ systems work, and I can’t see why there seems to be a need to provide ’simple’ – and wrong! – alternative ‘explanations’ when the real thing is so wonderful.

but surely if it does no harm… Alison Campbell Aug 16

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ResearchBlogging.org

There’s a lot been written in the blogosphere around what’s known as ‘complementary & alternative medicine.’ (I would argue that there’s no such thing – if it works ie improves/cures the patient’s health, then it’s medicine). In any debate around the use of CAM someone is likely to say that at least it does no harm. For things like homeopathy you could argue that since the client is swallowing only water or sugar pills, with no active principle present, then they’re highly unlikely to come to harm (witness the 10-21 homeopathic ‘overdose’). The counterargument here is that if the patient relies solely on homeopathy for anything beyond self-limiting conditions then there is in fact considerable potential for harm.

With other ‘treatments’ the potential for harm is more apparent. And in some cases the harm can be real. In the latest issue of the New Zealand Medical Journal, Brian Kennedy & Lutz Beckert report on the case of a woman whose acupunturist  left her with a case of pneumothorax. This is not a trivial problem: pneumothorax is where air builds up within the chest cavity, in the space round a lung, as the result of chest trauma or due to a spontaneous breach in the lung itself – or in this case, because an acupncture needle pierced the lung. This puts pressure on the lung, & as a result the lung collapses. (Pneumothorax has also had medical applications – in Sonja Davies‘ autobiography, Bread & Roses, she describes it as a treatment for tuberculosis. Apparently collapsing the affected lung makes it more difficult for the tuberculosis bacilli to survive & grow, so the lung has a chance to recover.)

In the case described by Kennedy & Beckert, the patient “became acutely short of breath, following introduction of an acupuncture needle into the right side of her chest posteriorly. She developed ‘tightness’ … and associated chest pain” & very sensibly left the clinic, went home, & called an ambulance when her symptoms (typical of pneumothorax) got worse. An X-ray showed that her lung has collapsed, & doctors used a needle to remove 450ml of air from the pleural space around the lung. The next morning the pneumothorax had recurred, which meant surgery to inset a ‘drain’ into htr chest wall. After the lung reinflated the drain was removed (& presumably the opening was sealed) & she went home a day later.

Madsen, Gotzsche & Hrobjartsson (2009) performed a meta-analysis of clinical trials looking at acupuncture as a treatment for pain. They looked at data from a total of 3025 patients who received either ‘real’ acupuncture, ’sham’ (placebo) acupuncture, & no treatment. Their conclusions: there was “a small analgesic effect of acupuncture …, which seems to lack clinical relevance and cannot be clearly distinguished from bias. Whether needling at acupuncture points, or at any site, reduces pain independently of the psychological impact of the treatment ritual is unclear.” (As Orac comments, on a related study, “the larger and better designed the study, the less likely it is to find a treatment effect greater than placebo due to the treatment.”)

Given the following that acupuncture appears to have, people will no doubt continue to seek it out for various ills, regardless of the fact that it performs no better than placebo. In which case, they need to be aware that adverse events like the one described by Kennedy & Beckert, although very rare, can still occur. (These authors list ”transmission of diseases, needle fragments left in the body, nerve damage, pneumothorax, pneumoperitoneum [air in the abdominal cavity], organ puncture, cardiac tamponade [accumulation of fluid around the heart] and osteomyelitis [a bone infection]” as major adverse events, albeit extremely rare ones.) They conclude that as these events are generally associated with poorly-trained practitioners, if people do seek out acupuncture treatment they should choose their practitioner carefully – and if treatment involves acupuncture of the chest wall, then the client should be warned about the risks of pneumothorax by the practitioner concerned.

But as Darcy says over on SciBlogs, why go down this route at all?

Brian Kennedy, & Lutz Beckert (2010). A case of acupuncture-induced pneumothorax The New Zealand Medical Journal, 123 (1320) http://www.nzma.org.nz/journal/123-1320/4258

M.V.Madsen, P.C.Gotzsche & A.Hrobjartsson (2009) Acupuncture treatment for pain: systematic review of randomised clinical trials with acupuncture, placebo acupuncture, and no acupuncture groups. BMJ 338: a3115

MMS – continued health claims for an industrial bleach Alison Campbell Aug 15

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I’ve written a couple of times about the so-called ‘Miracle Mineral Supplement’, aka MMS. A recent post over on Science-Based Medicine looks at some of the claims made for this stuff, which is simply sodium chlorite, ‘activated’ by being mixed with citrus juice – and at some of the potentially serious side-effects associated with its use. And just now one of my readers has e-mailed me:

I know you’ve covered the Miracle Mineral Supplement hawkers before. It’s fascinating how this particular dealer exploits the Medsafe NZ non-compliance letter to *enhance* their marketing! Indeed – how else could you read the following?:

Therefore, regardless of the many thousands of success stories worldwide; this website cannot and will not make any claims that MMS assists in the treatment of serious diseases or conditions; such as asthma, diabetes, heart disease, HIV/AIDS, cancer, leukaemia, malaria, hepatitis and others.

Have you been following the case of 15-year-old skeptic Rhys Morgan who got into a spat over MMS at a Crohn’s Disease support forum and has since been banned? He’s an articulate, brave young man. It’s an interesting story and got me digging back to look at your old posts. The comments surprised me. ..(I hadn’t heard of Rhys before, but now I’ve looked him up. He’s posted an excellent TwitVid here.)

There are some horrific threads on MMS by NZers that I’ve found while browsing this morning. This one makes me shiver.

I shivered too. As one writer on that particular thread points out, “MMS is a 28% sodium chlorite (NaClO2) solution that you are activating with 10% citric acid,” a process that releases chlorine dioxide. This last is not nice stuff at all (taken by mouth, high doses can result in nausea, vomiting, diarrhea, & if all this continues there’s the potential for severe dehydration. In fact the US Food & Drug Administration has put out an advisory warning against taking MMS, noting that “the product, when used as directed, produces an industrial bleach that can cause serious harm to health.”  Yet the purveyors of this stuff make all sorts of claims for it, including that it cures AIDS, for goodness’ sake!

And they support their claims with all sorts of pseudoscientific nonsense. The NZ dealer that my correspondent linked to claims that MMS isn’t really a miracle, it’s “just plain chemistry!” and states that

when a chlorine dioxide ion contacts a harmful pathogen, it instantly rips up to five electrons from the pathogen, in what can be likened to a microscopic explosion… harmless to us, but terminal for pathogens. The pathogen – an electron donor – is rendered harmless due to the involuntary surrendering of its electrons to the chlorine dioxide – an electron acceptor – and the resulting release of energy. Oxidised by the chlorine ion, the former pathogen becomes a harmless salt.

This isn’t chemistry at all: a) while ClO2 can dissociate in water to form ions, there’s no such thing as a ‘chlorine dioxide ion’; b) how, exactly, does ClO2 differentiate between harmful (pathogenic) and ‘friendly’ bacteria? They don’t have little labels identifying them, & in many cases an organism may be ‘friendly’ in some contexts & definitely disease-causing in others; and c) ClO2 is an oxidising agent & thus, indeed, an electron acceptor. But how the removal of any electrons from a bacterium – a complex living organism – would produce a ‘harmless salt’ is beyond me & would in fact require a rewriting of the rules of chemistry. (A ’salt’ is an ionic compound that get when you react an acid eg hydrochloric acid with a ‘base’ eg sodium hydroxide.)

The dealer also claims that chlorine dioxide is carried around the body by red blood cells, which supposedly make no distinction between this compound & oxygen. In fact, what this oxidising agent does is oxidise haemoglobin (the protein complex in red blood cells that carries oxygen) to produce methaemoglobin. Methaemoglobin cannot bind to oxygen, so high levels of ClO2 would reduce your blood’s ability to carry oxygen to your tissues – not good for you at all (headaches, shortness of breath, & fatigue are some of the symptoms of a high methaemoglobin titre in your blood).

I have to say, all this both saddens & puzzles me.It puzzles me, because I can’t understand how it is that people will accept marketing claims like  this. Is it because the snake-oil statements cast the world in black & white, while science (& science-based medicine) simply can’t, & won’t, guarantee a result? Is it because the snake oil offers an easy fix (albeit a potentially costly one – in more ways than one! - if you keep on using the stuff)? Is it symptomatic of a wider distrust of science itself?

learning in lectures is a two-way street Alison Campbell Jul 27

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I really enjoy my first-year bio classes, & one of the reasons for this is that the students respond to my questions and ask questions of their own. I’ve just read Marcus’s excellent post on what he’s learned from his students & it’s spurred me to write a bit about this too.

So, what’s so good about student questions? Well, as Marcus says, those questions, & the students’ responses to our own probing, can combine to tell us (ie the teachers) a lot about our students’ current understanding of a particular topic. And if it turns out that they don’t follow it, or have particular misconceptions, then there’s not really any sense in going on to the next topic regardless. You’d just be muddying the waters further. Unfortunately there’s a tendency to push on anyway; after all there’s so much other material to get through & surely the students can read up about the bits they don’t get, after the lecture’s over? But it doesn’t work like that, so heaps of kudos to Marcus for throwing out 3 of the ’set’ tut questions so that he & the class could focus on coming to terms with one key issue. (& if students in his class are reading this – you’ve got a really good teacher.)

The other thing is, you can just about guarantee that students’ questions will lead to me learning something new :-) Take moss, for example – a student question in a botany lecture led to my learning something quite fundamental about moss biology. So do bear with me while I set the scene…

You’ll sometimes see moss described as a ‘lower’ plant: mosses don’t have any xylem & phloem (the vascular tissues that transport water & nutrients around the plant. Their leaves generally lack a cuticle, which along with the lack of internal plumbing makes them very susceptible to dehydration; they don’t have roots, just ‘rhizoids’; and they use spores for dispersal.

By the way, mosses can tolerate extended periods of dehydration just fine. They go brown, shrivel up, to all intents & purposes look dead – but rehydrate them & bingo! they spring back into life. This poikilohydric lifestyle means that mosses can live in some pretty extreme environments, including mainland Antarctica (not the Antarctic peninsula), where they’re the most complex plant around. A bit like the plant equivalent of tardigrades, really :-)

Anyway, back to the spores. Mosses, like all plants & in fact like algae as well, have a life cycle that’s characterised by something known as ‘alternation of generations’. In algae, mosses & ferns this manifests itself as 2 separate plants: a gametophyte generation, which produces the gametes, and the spore-producing sporophyte. (In the gymnosperms & angiosperms you never actually see a separate gametophyte, it’s tucked away inside the tissues of the sporophyte, which is the familiar pine tree or rose bush.) This is quite a complex way to do things, & among the bits which my students struggle with, & which we consequently spend a bit of time on, is the number of chromosomes in the gametophyte & sporophyte.

Because plants ‘do it’ differently from animals. In terms of chromosome number, gametes are haploid - they contain just a single copy of each chromosome. In animals, gamete production & the type of cell division that produces them, meiosis, are very closely linked. But that’s not the case in plants. Here, meiosis takes place in the sporophyte & produces, not gametes, but haploid spores, which are then shed & dispersed by the wind. When they germinate, they grow into the gametophytes, which are thus also haploid. Some gametophytes are female, & produce eggs; others are male & produce sperm (but by mitosis, not meiosis, so there’s no further change in chromosome number). When a sperm fertilises an egg, this produces a diploid zygote (ie two copies of each chromosome), which goes on to grow into the sporophyte. (Hopefully there’s an embedded video here, but if that doesn’t show for you, you’ll find it here on Youtube.)

 

Well, we’d spent quite a bit of one lecture going through this (& subsequently spent a fair bit of 2 more), & then someone said: but what determines whether a gametophyte plant is male or female? And do you know, I didn’t have a clue. It just wasn’t a question that I’d thought to ask myself, & maybe you can put that down to the fact that I’m really a zoologist by training rather than a botanist, & maybe I’d just never thought about it :-) But my goodness, once that student woke me up to the fact that here was something fairly central to the subject we were talking about, I went off & found the answer.

It turns out that in moss, all sporophytes are XY. This means that meiosis will produce 2 types of spore: half of them will carry a Y chromosome, & grow into male gametophytes. The other half have an X chromosome & become female gametophytes. Said like that, it seems quite straightforward, & I was mentally kicking myself for not having thought about that earlier. And when I went to the next lecture & shared what I’d found out, I also made a point of thanking the students for asking that key question in the first place. Because without that I might still be blissfully ignorant on that question (& yes, I’m sure there are many others!).

Learning in lectures does indeed go both ways.

the implausibility of possum peppering Alison Campbell Jul 17

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This morning’s Waikato Times carried the following headline: Heavens aligning for fiery possium cure. Now, there’s a lot of pressure on to find viable alternatives to 1080 as a means of controlling possums, but somehow I don’t think the method described in the Times story is going to take off.

The news item tells us that possum skins burnt to ashes under the right alignment of the Moon and stars could be an alternative to 1080 – & the group promoting this is asking for $330,000 of Environment Waikato funding to demonstrate it. My first thought, on reading this, was ‘you have to be joking!’ Subsequent thoughts were much the same. Why? 

Well, the Times story goes on to quote the funding application:

The method requires an understanding of how energies from the universe affect life on Earth. The appropriate alignment of Earth, Moon, Venus and Scorpio at the time of burning is necessary if the method is to work well and possums are best harvested at this time. The carbon from the burnt skin interferes with the reproductive energy of the possum.

(And aparently the soil has to be damp when this mix is broadcast over pastures & forests.) Now, this is nothing more than a mix of pseudoscience & magical thinking; science it is not. The mention of planetary alignments & a sign of the zodiac signals that we’re hearing about astrology. The idea that the position of the planets & their alignment with arbitrarily-named random patterns of stars can have any influence on life on Earth has been tested - & found wanting. (You can read an extended summary of the original research here). To suggest that the same factors would have any impact on possums is to demonstrate magical thinking.

The vague, generalised mention of ‘energies’ is another clue that we’re dealing with pseudoscience. As Brian Dunning says, terms like energy fields, negative energy, chi, orgone, aura, psi, and trans-dimensional energy are utterly meaningless in any scientific context. Claims about ‘energy fields’ & their therapeutic application in humans have been debunked on more than one occasion (see here & here, for example), & there’s no good reason to expect that these nebulous constructs should exist in possums.

In other words, there’s no plausible mechanism by which ‘possum peppering’ might work. Tellingly. the  article tells us that a 1998 trial of possum peppering saw an increase in possum numbers, & a study published in the New Zeland Journal of Ecology similarly found no deterrent effect of the ‘treatment’.. It should be fairly straightforward to test ‘peppering’ in the lab (& for rather less than $300,000), but given that the results of previous studies are negative, any new trials should be funded by the method’s proponents, & not by EW ratepayers.

of octopodes & clever horses Alison Campbell Jul 13

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Over on SciBlogs Aimee has started a discussion around the apparent psychic powers of Paul, the octopus who’s claimed to have predicted the results of several games in the just-ended soccer World Cup. (Actually, if he could predict the outcomes of games, this would make him prescient, not psychic. Once a pedant, always a pedant, alas!)

This octopode seer has supposedly picked the correct outcome for (if I remember rightly) 7 games in a row. The odds of getting this by chance are 1 in 128, which sounds rather good really. But ‘runs’ of 7 in a row are not actually unusual if you toss a coin often enough. They just look spectacular if they happen when you begin tossing (or picking mussels in a box) - & even more special if you then stop tossing while you’re ahead…

But I wonder if we’re not looking at an example of the ‘clever Hans’ effect. Clever Hans was a horse who amazed German audiences in the 1890s with his ability to count. If his trainer/owner, Wilhelm Von Osten, asked Hans for the sum of 3 + 4, the horse would tap his forefoot on the ground 7 times; no more, & no less. Apparently he could also tell the time, & identify people by name… Anyway, Von Osten – & those in the audience – firmly believed that the animal was the Mastermind of the equine world, not least because Clever Hans performed just as well when his trainer was out of the room. However, psychologist Oskar Pfungst eventually demonstrated (on the basis of careful experimentation) that Hans was instead responding to unconscious cues from those asking the questions. For instance, when those present didn’t know the answer to a question, the horse was equally stumped. It turned out that the animal was responding to changes in posture or expression: the questioner would tense up as Hans’s foot-tapping approached the correct answer, & relax when he reached it. The horse was certainly intelligent, but not a mathematician :-)

Now, cephalopods are also intelligent. The ‘clever Hans’ effect is a much more parsimonious explanation for Paul’s apparent predictive powers than the suggestion that a tentacled mollusc with a completely different brain (&, presumably, experience of the world) might be capable of predicting the outcome of a game played by a bunch of ball-kicking bipeds :-)

the skills of critical thinking Alison Campbell Jul 11

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Those of you who are thinking of entering for the Scholarship Biology exam at the end of the year may have had a look at the statement of just what is expected (the ‘performance descriptors’). If you have, you’ll have seen that one of the key attributes you need to demonstrate is an ability to think criticaly: about the question; about the supporting materials that the examiner may have provided; about your own knowledge (you don’t want to do a brain dump, after all – this will not impress the examiner one bit!).

I’ve written quite a bit about this in the past (here, here, & here, for example). Today I thought I’d add to that, with a closer look at some of the questions that you, as a critical thinker, might ask about a topic. (This is a modified version of something I’ve posted on the ‘other’ blog, Talking Teaching, wihich I share with my colleagues Marcus & Fabiana.)

At the end of my last Talking Teaching post I mentioned critical thinking – & said I’d leave that topic till later. This is ‘later’ :-)

If you ask a teacher to list the attributes that they’d like to see in their students when they move on to further education, then ‘critical thinking’ will feature somewhere on that list. It’ll probably be in most tertiary institutions’ ‘graduate profiles’ as well. What I’d like to consider is, do our students measure up to that aspiration? How well do we help them to become critical thinkers?  (That last means, not just talking about it, but modelling critical thinking skills for our students - & giving them the opportunity to practice! They’ll only learn by doing.)

What is a critical thinker, anyway? I’ve heard it said that a critical thinker is someone who has an open mind on issues under discussion - but not so open that their brains fall out! When faced with a given position statement (‘therapeutic touch really works’; ‘intelligent design explains biodiversity better than evolution’; ‘scientists are wrong about global warming’; & so on), someone who thinks critically will ask things like:

  • What is the source of your information?
  • What assumptions are you making?
  • Is a different conclusion more consistent with the data?
  • What is an alternate explanation for this phenomenon?

These are ‘Socratic questions’ (if you’re working towards Schol exams, I’d suggest following that link & having a look at the entire list). Over at Skeptoid, Brian Dunning offers a good introduction to the use of these questions. And he makes a very important point. The end point of critical thinking (skepticism, if you like) should not be simply the debunking of a particular point of view. That’s not exactly helpful (even if it does provide temporary satisfaction to the debunker!) As Dunning says, “Skepticism is about applying the scientific method to arrive at a conclusion that is evidenced to be beneficial…” In other words, it’s not enough to demonstrate why a point of view is incorrect – you need to produce an interpretation or explanation that better fits the available evidence, and ideally one that can be usefully applied to solve a problem.

And learning to do that takes time. And practice.

And maybe listening to some of the Skeptoid podcasts - I know I’ve learned a lot from those myself :-)

are octopuses really psychic? Alison Campbell Jul 09

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If, like me, you enjoy soccer you’ll have been excitedly following the World Cup games. You will probably have caught some of the other hoop-la – including the ‘news’ coverage of an octopus that purportedly ‘predicted’ the outcome of games involving the German team. Now, I’ve been bemused by the coverage accorded to this cephalopod ‘psychic’ – does the press really think Paul the octopus can predict the outcome of a soccer game? I’d like to be charitable & think it’s just reporters looking for a ‘feel-good’ story, or misunderstanding the nature of probability…

After all, let’s look at what the octopus is doing. Offered 2 flag-bearing boxes (one with the German flag, one with the opponent’s), each containing a mussel, he chooses one of them. For the 6 matches involving the German team he appeared to select the winner of each game, including the one that saw Germany go home & Spain progress to the final of the world cup. (A rather tedious game, I have to say…)

Gasp! Surely this is due to more than chance? Well, no. If you toss a coin & record whether it comes up heads or tails, over (say) 100 tosses you’ll see ‘runs’ of several heads or several tails. But each time you toss, regardless of what’s gone before, there’s a 1 in 2 chance of coming up heads. And that’s probably what we’re seeing here. Offer Paul the same choices, multiple times, & I’d predict that you’d see similar results – sometimes he’d be right, & sometimes wrong, & sometimes there’d be a run of correct ‘choices’. (But no-one’s going to do that, of course, because they don’t see a story in it.) However, humans are pattern-seeking creatures & we seem predisposed to imbue mere coincidence with far more meaning than it actually has. And given the amount of press coverage given to self-proclaimed psychics of the human variety, perhaps I shouldn’t be too surprised that the octopus, too, has gained his moment of fame.

positive allometry & the prehistory of sexual selection Alison Campbell Jul 06

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ResearchBlogging.org

Thanks to herr doktor bimler & the University’s science librarian, I now have my hands on two copies of the paper I mentioned a couple of posts ago: Positive allometry & the prehistory of sexual selection (Tomkins et al., 2010). The term ‘allometry’ refers to the relationship between the size of an organism & the size of various parts of that organism. When scientists study allometry, they might do this for various stages in the growth of an individual, or they might compare different organisms of the same species, or individuals from separate species. ‘Positive’ allometry means that as body size increases, so does the size of whatever other feature’s being examined. (The Panda’s Thumb has an example of this, for body size: brain size ratios in primates.) The paper by Tomkins et al. looks at the spiny ’sails’ on the backs of pelycosaurs & the crests on pterosaurs’ heads, and suggests that differences in size between male & female individuals is related to sexual selection.

When I first saw the newspaper report on this article, I wondered: just how did the authors identify male & female pelycosaurs & pterosaurs? With modern reptiles size can be a cue, as can colours & crests & inflatable throat pouches. (Sexual dimorphism is widespread in reptiles, but unfortunately it’s not consistent: in some groups the males are larger, but in others it’s the females.) And of course, hypotheses about which sex you might be looking at can be confirmed by watching to see who’s on top during mating. And also by dissection: the ‘who’s on top’ method wouldn’t work for some whiptail lizard species, where all individuals are female & reproduction is by parthenogenesis. In these species, individuals take on the ‘male’ or ‘female’ role during mating depending on the levels of oestrogen & testosterone in their blood.  So I was interested to know how the authors determined whether they were looking at a male or female in dealing with any particular indivdiual.

The ’standard’ explanation for pteranodon crests & pelycosaur sails is that they were related to thermoregulation. Pelycosaurs were unlikely to be endotherms, generating heat internally as a side-effect of a high metabolic rate, & so like modern reptiles would have had to bask in the sun to warm their bodies before dashing around chasing prey (or avoiding being prey). As Tomkins & his colleagues point out, a ’sail’ of tissue supported by vertebral spines, with blood vessels running through it, could have warmed the animal’s blood more rapidly – a bit like a solar panel used to heat water. It could equally have acted like a car radiator & shed excess heat. (I need to add that not all pelycosaurs had these sails.) Something similar’s been proposed for pteranosaur crests, although here there are other hypotheses, including acting as rudders in flight, or in courtship displays - in which case there could have been sexual selection operating. Certainly sexual selection can generate some quite extreme traits – the peacock’s tail is just one example. Tomkins et al. comment that “[p]ositive interspecific allometry occurs in the sexually selected traits of a range of [living species]“, & hypothesise that significant allometry in these two extinct taxa may also be explained by sexual selection.

For their examination of allometry in pterosaurs they used 9 skulls from Pteranodon longiceps - none of these skulls were associated with other skeletal bits & pieces from which to obtain a measure of body size. So the assumption here must be that the bigger heads/crests came from bigger-bodied individuals. Some support for this assumption came from an examination of the size of the eye socket: as you might expect this increased in size as the skulls got bigger – but in living reptiles the diameter of the eye socket is directly correlated with an increase in body size as well. However, as herr doktor pointed out in my earlier post’s comments, the individual pterosaurs are described as ‘putative’ males (N = 6) & females (N = 3) i.e. they’ve been tentatively classified as male & female on an unspecified basis. If the classification was based on size, then this is something of an a priori assumption that could colour the results. In addition, the smallest ‘putatively male’ skull is the same size as the 3 ‘putatively female’ skulls, with the same sized crest. It’s hard to see strong evidence of sexual selection in these data. I wonder if an alternate possibility could be an age series? Reptiles do increase in size as they age, within species-specific limits, so smaller skulls & crests could simply be those of younger indivdiuals.

In their analysis of Dimetrodon, the team didn’t have access to enough individuals of one species to look at intraspecific allometry. Instead, they used data from 7 Dimetrodon species, & found that the sail size did increase with an increase in body size from one species to another. But sexual selection – again, I’d like to see an explanation of just how the authors determined the sex of the individual animals concerned, & how they ruled out the possibility that they were looking at age-related size differences within particular species. Having said that, the authors do note that the sails of smaller dimetrodonts would not have had much positive effect on thermoregulation & might actually have been a thermoregulatory liability, radiating heat so fast in cooler conditions that the animals would have chilled very rapidly.

Basically, the sexual selection hypothesis as an explanation for the adornments of Dimetrodon & Pteranodon is an interesting one, but we need to see data from many more specimens, & a clear method of sexing the remains, to test it further.

Tomkins JL, Lebas NR, Witton MP, Martill DM, & Humphries S (2010). Positive Allometry and the Prehistory of Sexual Selection. The American naturalist PMID: 20565262 doi:10.1086/653001

And I see that Brian Switek has beaten me to it… 

another early hominin specimen, & other things to read Alison Campbell Jun 27

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I’m catching up on my reading of other people’s blogs, so here are some interesting posts to share with you.

At Laelaps Brian Switek has commented on the latest fossil hominin find. Dubbed ‘Kadanuumuu’ (or ‘Big Man’), this is a partial Australopithecus afarensis skeleton.Kadanuumuu was much larger than the more familiar (& more recent) ‘Lucy’, & because of this & because of features of the pelvis, the scientists who described the remains feel they were probably those of a male. There’s also the suggestion (see the comments thread for Brian’s article) that these remains may overturn the current hypothesis that afarensis’s ribcage was funnel-shaped. Or may not – we probably need more data on this one.

There’s an interesting discussion on Pharyngula  around the separation of science & belief. Part of the post, & the ensuing comments thread, focus on a post by another blogger that appears to be making an argument for students’ personal beliefs to count as valid answers in science exams. Every now & then I’ve seen a student answer a question in this way, rather than giving a reasoned scientific response to said question. In each case I have marked them down, & it’s not because I deny students the right to personal belief systems. It’s because the question has been science-based, & that’s what I expect the answer to be as well. Anyway, the post & discussion are interesting & thought-provoking.

And the Silly Beliefs team have taken a critical look at a recent item on ‘60 Minutes’ that took an extremely credulous stance on the issue of UFOs & alien visitations. I had wondered whether to watch the program but the promos made me think that this would do damage to my blood pressure. Presenting information that turns out to be at least a decade old as something new & exciting doesn’t strike me as particularly good journalism…

Enjoy :-)

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