Friday, 27 February 2015

Limpets and F1 cars

An article on the Sky News web site had the headline: Does Humble Limpet Hold Key To Future F1 Cars? It referred to the findings of Asa Barber and colleagues on the strength of limpet teeth (there were many other reports of this work in the Media, most with catchy headlines). Intrigued, I read the original publication describing the detailed studies and the comparisons made by the authors between the strength of limpet teeth and strong, Man-made materials. In the paper [1], there was none of the colourful reporting that I had seen in newspapers and on the web.

The teeth of limpets are set on the radula (see above), a rasping tongue, used to scrape rock surfaces and thus acquire food from attached algal and microbial biofilms. In moving over stone surfaces, the teeth “need to be extremely strong and hard to avoid catastrophic failure” although the scraping action does cause them to become worn [1]. Strength comes from a mineral, goethite (iron oxy hydroxide), that is formed in filaments within a matrix of protein with the “mineral nanofibres typically many micrometres in length but only a few tens of nanometers in diameter” [1]. In non-technical language, the strengthening filaments are long and very thin and this provides the optimum arrangement for resilience.

Limpets are very common around shores and are certainly successful snails (members of the Class Gastropoda). As I was brought up by the sea, I became fascinated by marine organisms and their habits and, like many children, was intrigued by the ability of limpets to cling on to rocks and thus resist any amount of kicking by me. I learned that this attachment was made possible by the muscular foot and was not related to suction as I had thought. The foot has numerous minute extensions over its base and these interface with the (microscopically) rough surface to which the limpet is attached, a thin film of mucus ensuring good contact. This tight attachment serves not only to prevent limpets from being removed, but also allows a near perfect match between the shell and the rock, minimising water loss when the tide is out. The attachment is so close that the rock can become eroded into “home scars” and the margin of the shell follows contours, like those created by the barnacles in the illustration below.

Everything changes when the tide comes in. The tight hold is relaxed and the limpets now use their foot, and secreted mucus, to glide over the surface, just like other snails. It is then that they feed by movements of the radula and this leaves a characteristic trail of removed biofilm (see below - and for further, excellent pictures see As some limpets are territorial, it is thought that local areas of biofilm is then “farmed” by individuals and their excretions may well act as fertiliser, as it is known that biofilm components are highly adsorptive [2]. Algae also grow on the home scars [3] and these will again be fertilised by the limpet during attachment; exposure to light allowing the algae to photosynthesise when the limpets forage away from the home scar.

The findings of Barber et al., and our knowledge of the Natural History of limpets, bring to mind many questions: “How did the structure of limpet teeth evolve?”; “How did mineral fibres become embedded in a protein matrix?”, “How did teeth become arranged on a radula?”; “How was a radula formed?”; “How did the structure of the foot develop?”; “How did limpets become territorial and develop the habit of gardening?”; etc. These questions have no easy answers.

We tend to regard animals like limpets as being mundane and lacking in interest, although they are valued as food, especially in Madeira, where an annual festival is held in their honour. This doesn’t extend to considering the welfare of the limpets, especially as they are fried alive in butter, before the addition of a little garlic and lemon juice makes them a tasty treat. Their use as food, and as examples of useful bioengineering, emphasises our anthropocentric approach and we rightly continue to have this attitude. However, we should also step back and admire how evolution has resulted in such an impressive array of adaptations to life on the rocky shore. The child in me has a sense of awe at the selection of mutations that allowed all the changes that have occurred through time to produce such wonderful creatures. I’m not suggesting that limpets should be regarded as honorary humans, in the way that we regard our pets, but these splendid snails are not just around for our purposes, whatever the sentiments of the Book of Genesis, or the impressions provided by headlines in the Media. All the adaptations referred to in the questions above were in place long before humans appeared and limpets deserve our respect.

[1] Asa H. Barber, Dun Lu and Nicola M Pugno (2015) Extreme strength observed in limpet teeth. Journal of the Royal Society Interface 12: 20141326.

[2] Roger S Wotton (2004) The essential role of exopolymers (EPS) in aquatic systems. Oceanography and Marine Biology, An Annual Review 42: 57-94.

[3] Gray A Williams and Colin Little (2001) Preliminary observations on algal growth under limpet (Patella vulgata) home scars. Journal of the Marine Biological Association of the United Kingdom 81: 175-176.

Monday, 16 February 2015

Giotto, Angels, and Heaven

Giotto broke with the Byzantine tradition and used “naturalness” and 3-dimensional portrayals in his work. The sixteenth century biographer Giorgio Vasari writes colourfully about Giotto and his status in the History of Art [1]:

The gratitude which the masters in painting owe to nature - who is ever the truest model of him who, possessing the power to select the brightest parts from her best and loveliest features, employs himself unweariedly in the reproduction of these beauties - this gratitude, I say, is due, in my judgement, to the Florentine painter, Giotto, seeing that he alone - although born amidst incapable artists, and at a time when all good methods in art had long been entombed beneath the ruins of war - yet, by the favour of Heaven, he, I say, alone succeeded in resuscitating art, and restoring her to a path that may be called the true one.

Vasari goes on to describe how the young Giotto, drawing on stones while looking after his father’s sheep, was seen by Cimabue who marvelled at his natural skill and took him into his studio. Giotto soon eclipsed his master and later became much in demand as a painter of religious subjects in chapels and other holy places, among the most famous works being the frescoes in the Capella della Scrovegni (Arena Chapel) in Padua [2]. 

Although the main human figures in each of the frescoes demonstrate the ability of a great artist, I am drawn to the angels (some of which are shown below), especially those described by Anne Holmes that “float like modern hang-gliders” [3].

Having discussed the inability of angels to use flapping flight (unless they fly by mystical forces) [4], Giotto’s hang-glider angels are of special interest to me, as it is implied that they use gliding flight. Their costumes break up around their base as the angels fly rapidly toward Earth and this was probably intended to convey speed and not, as one wag suggested, the first signs of burning up on entry into the Earth’s atmosphere. Giotto liked “jests and witty retorts” [1] but this is unlikely to be one of them. He was a close observer of the sky and “painted the first naturalistic depiction of a comet in his scene of the Adoration of the Magi [see below]” [5], so it is not inconceivable that his idea for the breaking up of the angels’ costumes came from observations of meteors.

The late Sidney J. Blatt, the distinguished psychologist at Yale University, turned a psychoanalyst’s eye on the Giotto frescoes in Padua and on the artist’s use of naturalness [6].  He writes:

Giotto was influenced by the Franciscan Weltanschauung, and his narrative frescoes in the Scrovegni Chapel present biblical stories as human situations with which the viewer could identify. Saints were portrayed not only as remote, transcendental spirits but as people who experienced a wide range of emotions, from pleasure to anguish, joy to despair.. ..Giotto’s figures have depth and volume, are presented from various vantage points including profile, rear, and three-quarter views, and express vivid emotion in their gestures and facial expressions.. ..Giotto’s visual narratives enabled the illiterate to become more familiar with biblical stories. His realism reduced the distance between man and God by representing religious narratives not as sacred stories but as natural, spontaneous interactions among people.

The main focus of our attention in the frescoes are the events unfolding on Earth, but the angels also show facial expressions, albeit not in the detail of the figures on the ground. If Giotto was trying to convey emotions, what was going through the mind of the angel that seems to show pain, or horror, at having to pull up near vertically (see below)? The wag mentioned earlier suggested it might be because the angel was going into a dangerous stall and needed to recover, but this facetious comment does little to answer the question.

Further in his article, Blatt [6] points out that:

..Giotto alluded to infinity.. using celestial blue as the background color of his Padua frescoes rather than the reflective, impenetrable gold used so often in medieval art.. ..The suggestion of infinity of nature in Giotto’s Padua frescoes was an important step in the replacement of the closed world of the ancients by the open world of the moderns. The Giotto frescoes implicitly encourage man not to be terrified of infinity or to leave it to God but to try to comprehend and use it as a fundamental concept in the study of nature, not only in art, but in literature, philosophy, mathematics, and science as well.

This is a profound comment and ties Giotto to the beginnings of the “Scientific Revolution” at the beginning of the Renaissance. However, religious subjects provide a challenge. For example, where was Heaven? The idea of angels with bird wings makes Heaven feel close to the Earth, and angels could then commute relatively easily. Winged angels appear in art from ancient times and Giotto continues that tradition, as did subsequent artists, and we are still happy with this imagery today. Does that mean we feel that Heaven is a real place - and are comforted that it is nearby? If so, where is it?

[1] Giorgio Vasari (2005) Vasari’s Lives of the Artists (translated by Mrs Jonathan Foster). New York, Dover Publication, Inc. [Ooriginal from 1550, with a revised Second Edition in 1568]

[3] Anne Holmes (1996) Giotto’s Angels. The Times Literary Supplement 4880:19

[5] Roberta J. M. Olson and Jay M. Pasachoff (2001) Moon-struck: artists rediscover Nature and observe. Earth, Moon and Planets 85-86: 303-341.

[6] Sidney J. Blatt (1994) A psychoanalytic appreciation of Giotto’s mode of artistic representation and its implications for Renaissance Art and Science. The Psychoanalytic Study of the Child 49: 365-393.

Sunday, 8 February 2015

Crows and impending doom

We project emotions on to crows. Being black, their feathers have the Western colour of mourning and they have become associated with impending doom.

Two paintings sum up this projection. In the first of these, Van Gogh’s Wheatfield with Crows of 1890 [1] the colouring is sombre and crows are flying towards us. Although I am not a fan of most of van Gogh’s work, this painting had a powerful impact on me when I first saw it and it is the crows, painted with crude strokes, that carry most of the threat of something bad about to happen. There are more than 40 of them (were they rooks, the close relatives of crows and known to be more social?) and they fly obliquely towards the observer from a distant point in the dark and threatening sky.

The second painting, Boy with a Crow, was completed in 1884 [2], six years earlier than the work by Van Gogh, when the artist, Akseli Gallen-Kallela was just nineteen years old. This painting is less well known than Wheatfield with Crows but it matches it, or even surpasses it, for the threat of bad times, especially as the victim of potential misfortune is also included. A young boy looks over a small patch of ground to something in the distance, but out of the picture. Meanwhile, a solitarily hooded crow is pecking at the ground and looking at the boy with its left eye. That patch of land, probably part of a larger plot, may be essential for grazing by animals and thus survival of a young family, for the climate in Finland is harsh for half of the year and the barefooted boy’s clothes show that his parents are poor.

It is not only the black colour of crows that provides a sense of threat, but knowing that they, and their close relatives, feed on carrion, although this is only part of the diet [3, 4]. We have an aversion to carrion, and to animals that feed on dead bodies, while recognising that carrion feeding is an essential part of the normal functioning of ecosystems. Our feelings about feeding on already dead bodies is not confined to crows: compare our admiration for eagles capturing, and killing, their prey with our view of squabbling vultures at the remains of a lion kill and, while mentioning lions, compare our reaction to seeing these big cats bring down a zebra, or wildebeest, with our attitude towards hyenas finishing off the carcase and eating the bones. Eagles and lions are considered noble and powerful (they are even combined in mythical gryphons), whereas vultures and hyenas are somehow skulking and despicable.

Crows are intelligent and successful birds and, like vultures and hyenas, do not deserve their reputation. However, that reputation sticks. Imagine our reaction to Van Gogh’s painting if it was parrots flying towards us, or, in Gallen-Kallela’s masterpiece, if it was a duck that was looking askance at the boy?

[3] J.D.Lockie (1956) The Food and Feeding Behaviour of the Jackdaw, Rook and Carrion Crow. Journal of Animal Ecology 25: 421-428.

[4] Roger Tory Peterson, Guy Mountfort and P.A.D.Hollom (1993) Collins Field Guide to the Birds of Britain and Europe. London, HarperCollins.