Tuesday 26 May 2015

The bones betray

I've suggested that, for about 100 years, anatomy has been considered rather old hat, all the namers-of-parts being long dead:
  • Islets of Langerhans (1847-1888)
  • Malpighian (1628-1694) pyramids
  • Purkinje (aka Purkyně 1787-1869) fibres
  • Golgi (1843–1926) body
  • Broca's (1824–1880) area
  • Fallopian (1523–1562) tubes
  • Haversian (1657–1702) canals
  • Crypts of Lieberkühn (1711-1756)
But with 3-D printing and other technologies, anatomy has moved front and centre in competition for the limelight of medical sexiness. Comparative anatomy has always been a minority sport because it's hard to find anything monetisable=useful in knowledge of the homology of a bat's wing, a whale's flipper and the hands which are now diligently hunting over the key-board.  I guess that's fair enough but I still find it all fascinating.  Perhaps it's just that I find any deep knowledge fascinating; heck, I could spend an hour listening to someone who collects match-boxes or is the county Donkey-Kong champion.

Neil Shubin is the Robert R. Bensley Professor of Organismal Biology and Anatomy [POBA?] at U. Chicago and also Provost of the Field Museum of Natural History, so he's Emilie Graslie's boss.  He's written a book Your Inner Fish and this is a review.  I'm sure you can find other reviews [Grauniad] on line and if you live in the right part of the world you can see three PBS episodes based on the book.  Or for a flavor of the issues and their resolution try this youtube lecture. It's a wonderful story of a serendipitous encounter with an atlas which sent Shubin and Co. to the Arctic to look at 350 mya tropical river sediments. There they found Tiktaalik roseae a strange Devonian lobed-finned fish (it's definitely a fish with scales and gills) that could do push-ups: it has a structural rib-cage and pectoral girdle that would have allowed its fore-fins to propel the beast across the land between ponds. The rib-cage also contained lungs Importantly, it has a neck so it can look around and admire the view from topside.  These missing links are important for understanding where we came from and the descriptive paper made Nature although not the cover. Your Inner Fish is a wide-ranging discourse on how the past can explain the present notably by using the concept of homology - the shared ancestry of structures that don't obviously look as if they have much in common.

There are three tiny bones in each of your middle ears: incus, malleus and stapes [anvil, hammer and stirrup to chaps who didn't have Latin in the education]. The incus and malleus form a hinge/lever that gives mechanical advantage to the sound waves that strike the ear-drum.  That hinge has been re-purposed from the articulation of a reptile jaw!  The hinge was too useful to discard when mammals developed a new jaw with fancier teeth stuck into a single bone called the mandible which articulates directly with the skull and so streamlines the engineering of chomp. That's how evolution works: by tinkering around with what we already have to create something new.  "Tinkering" in English implies rather feeble piffling about; François Jacob's French equivalent bricolage sounds to my ear more like giving some recalcitrant thing a few good dings with a hammer to make it fit.

Like Gollum Shubin gets weaker as he gets further from the magic seams of Devonian (420-360mya) fossil beds but he deserves credit for putting an evolutionary gloss on a great many puzzles of the vertebrate-mammalian-human condition. Coming from the United Theocracy of America scientists need to launch the SS Evolution whenever possible into the complacent warm waves of creationism. But pushing out a leaky, poorly manned vessel is just providing food for the biblefish. He 'explains' obesity and heart-disease . . . and hemorrhoids for good measure in 2.5 pages! An explanation of obesity without mentioning the gut flora is wrong inadequate. I have more to say on the nuance of obesity.  The last third of Subin's book is like a blog without a good sub-editor:  whatever-you're-having-yourself is run out into the public domain without it being properly developed and almost immediately segues into another intriguing sort-of-related topic. In Shubin's case the obesity+ chapter is followed immediately by a trivialisation of the connexion between sleep apnea (which is indeed more frequent among the obese), choking and our ability to speak. Much the same sort of problems beset The Blob but I'm not selling it (yet!) for £9.99. But it's okay in this sense: if Shubin makes you think "hmmmm, that's odd" then that makes him worth the read and he is scientist enough to have 12 tiny-print pages of references to help us follow things up at the end of the book.
"The most exciting phrase to hear in science, the one that heralds 
new discoveries, is not 'Eureka!' but 'That's funny...'"  Isaac Azimov.

One of those "can that be true??" anecdotes concerns a peculiarity of cetacea [whales and dolphins] whose ancestry we were recently reporting. All mammals have something in excess of 1,000 different olfactory receptors [proteins that sit in the membrane of cells in the olfactory epithelium] up our noses.  They are interesting because we have almost as many as blood-hounds and yet we don't consciously pay much attention to smells. Yes, yes, we all hold our noses and shriek when farmers are spreading pig-slurry and most of us respond to fresh-brewed coffee or vanilla or geraniums but we don't know when our partner is ovulating and we scrub our armpits far too much and far too often. It's probably true for many heterosexual blokes that she is receptive when he is drunk. But it's clear that some part of our brain is indeed taking in olfactory signals: mothers can identify their children's clothes in the dark; sororities synchronise their cycles or not; and apparently we sniff our hands a lot.  Nevertheless, a great many of our olfactory receptor genes have become "pseudogenes": mutations have accumulated so that the genes are no longer functional.  Shubin asserts that all the olfactory receptors in whales have become pseudogenes as their nostrils have been bricolagé into a blow-hole at the top of their heads. There is nothing useful to smell top-side and when submerged the epithelium is awash with salt-water which somehow has made the air-adapted olfactory receptors non-functional. That seems to be the argument aNNyway. I feel an under-graduate research project coming on: there are two reasonably complete cetacean genomes that have been sequenced; Dolphin Tursiops truncatus and Sperm whale Physter macrocephalus.  We can trawl through the sequence data to see just how broken their smell-repertoire is.

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