The beginning and the end of the Anthropocene

Is there an Anthropocene? This question is being debated currently and a report is to be published in 2016 on whether a geological epoch created by the transformative activities of Homo sapiens should be defined, and what should mark its beginning. According to Richard Monastersky [1]:

A committee of researchers is currently hashing out whether to codify the Anthropocene as a formal geological unit, and when to define its starting point.. .. The push to formalize the Anthropocene upsets some stratigraphers.. ..One major question is whether there really are significant records of the Anthropocene in global stratigraphy.. ..Some researchers argue that it is too soon to make a decision – it will take centuries or longer to know what lasting impact humans are having on the planet.

Monastersky then quotes from Erle Ellis, a Geographer at the University of Maryland:

"We should set a time, perhaps 1000 years from now, in which we would officially investigate this.. ..Making a decision before then would be premature."

Discussion about the Anthropocene thus reflects a typical debate among scientists and other academics having different views of what marks a definable stratigraphic boundary.

As Monastersky points out, markers could be from the Industrial Revolution, or from the radioisotope signatures resulting from atmospheric testing of nuclear weapons that ceased in the 1960s. While supporting the case for 1964 as the beginning of the Anthropocene, Lewis and Maslin [2] also put forward a strong argument for using the measurable decrease in atmospheric carbon dioxide between 1570 and 1620 (with a minimum in 1610), something that they relate to the effects of New World colonisation and dramatic changes in human population density, changes in diet and agricultural practices brought by new foods, and the development of increased trade based on industrial production. Their selection of 1610 adds another part to the Anthropocene debate, but their paper also contains an interesting review of human impacts in the very short time that Homo sapiens has been the dominant species on the Earth.

In conclusion, Lewis and Maslin write [2]:

Past scientific discoveries have tended to shift perceptions away from a view of humanity as occupying the centre of the Universe. In 1543 Copernicus's observation of the Earth revolving around the Sun demonstrated that this is not the case. The implications of Darwin's 1859 discoveries then established that Homo sapiens is simply part of the tree of life with no special origin. Adopting the Anthropocene may reverse this trend by asserting that humans are not passive observers of Earth's functioning. To a large extent the future of the only place where life is known to exist is being determined by the actions of humans. Yet, the power that humans wield is unlike any other force of nature, because it is reflexive and therefore can be used, withdrawn or modified. More widespread recognition that human actions are driving far-reaching changes to the life-supporting infrastructure of Earth may well have increasing philosophical, social, economic and political implications over the coming decades.

Whether the Anthropocene should be defined, and what its definition should be, seem trifling issues compared with those raised in that last paragraph. Whether the Anthropocene began in 1610 or 1964, it has the potential to be one of the shortest epochs thus far. The end of a geological time period is usually marked by large-scale events such as asteroid impacts, widespread upheavals in the Earth’s crust, or dramatic changes in climate. We don’t know how the Anthropocene will end and it may be from one of these causes and thus be outside human control. Alternatively, the epoch may end as a direct result of human actions. We know how destructive we have already been, and continue to be; with wars, global warming, widespread removal of forests, extinction of populations, introduction of poisons and antibiotics, etc. all being major impacts. There are those who feel that we should be able to overcome the many difficulties we face using technological solutions but, while I admire human invention, I do not feel optimistic about the future. The dominant economic system is based on growth and growth cannot be sustained indefinitely, so those of us in the Developed World will no longer be able to cocoon ourselves in warmed (or cooled) buildings and we may need to hunt and forage to obtain food. The social crises that result from a catastrophic fall in living standards can be imagined.

This is preachy, but our way of life, and its characteristic complacency, is highly damaging for other organisms on Earth and, like all the others, our epoch will end. The Anthropocene will be followed by another epoch, but what organisms will dominate? After our controlling influence is no longer present, the environment will again be the main vehicle for selection of changes in genes (a natural mechanism that we override). Bacteria and other unicellular organisms are sure to survive the cataclysmic events at the end of the Anthropocene, but what about other organisms? Will evolution result inevitably in a dominant form that makes drastic changes to its surroundings, or will there be a less destructive solution to the relationship between organisms and their environment?

[1] Richard Monastersky (2015) The human age. Nature 519: 144-147.

[2] Simon L. Lewis and Mark A. Maslin (2015) Defining the Anthropocene. Nature 519: 171-180.

Eating limpets

In my last blog post, I wrote an appreciation of limpets and the extraordinary adaptations that they show for life on rocky marine shores [1]. As I pointed out, that should not prevent us from using these molluscs as a source of food and that is something that fits with contemporary debates about sustainability and the need for animal protein. We are now much less resourceful than our ancestors, and are dependent on what is available in stores or on market stalls, with the latter often showing a more local approach than the former.

To gain an historical perspective on eating limpets, I read Lovell's The Edible Molluscs of Great Britain and Ireland with Recipes for cooking them [2] and he describes their consumption by some communities:

"In many places limpets are used for food, especially on the Continent, where they are oftener eaten than the periwinkle. At Naples they make them into soup, and I am told it is an excellent dish.. ..The poorer classes at Eastbourne eat them constantly.. ..At Plymouth they gather great numbers of them, especially from the breakwater, as well as in the Isle of Man, where they are known by the name of "flitters"; and in Scotland the juice of these shellfishes is mixed with oatmeal.."

In addition to this background information, Lovell also gives recipes [2]:

"Limpet Soup – Wash them, and free the shells from seaweeds etc.; put them into a saucepan and parboil them. Take them out of the shells; chop up some parsley, and put it, with a tablespoonful of oil, or an ounce of lard or butter, into a saucepan, and fry until it becomes brown. Add a pint of water, and, when boiling, throw in the limpets, with a teaspoonful of anchovy sauce, some pepper, and boil again for half an hour; or, if preferred, stew them before putting them into the soup.

Limpet sauce – Choose clean-shelled limpets, not covered with barnacles, steep them in fresh water, and then heat them in a close covered saucepan until they part easily from the shells. They yield a rich brown liquor, in which, after being shelled, they may be stewed for half an hour. Thicken the liquor with butter and flour; strain and season with pepper, cayenne, and salt, and a slight flavouring of lemon-juice or vinegar. The limpets, being tough and indigestible, are not returned into the sauce."

The latter comment reminds us of the common failing of over-cooking seafood of all kinds, something that one learns by trial and error.

Lovell [2] also gives a more rustic approach to cooking limpets, originating from the island of Herm in the Channel Islands, and reported by Jeffreys in Volume 3 of his British Conchology:

"Roasted limpets - The limpets were placed on the ground, and laid in their usual position, and cooked by being covered with a heap of straw, which had been set on fire, about twenty minutes before dinner."

To these recipes can be added others from different parts of the World (illustrations of each dish are given, with the URL to the web page for each recipe):

Hawaiian grilled limpet: http://www.cookingchanneltv.com/recipes/grilled-fresh-opihi-limpet.html

Limpets with spaghetti: http://www.ideapesce.it/ricetta/spaghetti-con-patelle

Limpets with rice: http://www.easyportugueserecipes.com/wordpress/azorean-clams-and-rice-lapas-com-arroz/

Grilled Limpets in the Azores style: http://myrestaurant.pt/en/recipes/grilled-limpets-azores-style

It is only possible to eat limpets as a regular part of the diet if one lives at, or near, the coast. For those who are landlocked, Lovell guides us to Garden Snails, together with their close relatives, including the Roman, or Vine, Snail (and who doesn't like Escargots à la Bourguinonne?). Limpets and land snails are both sustainable foods and provide good sources of animal protein. Although I don't feel comfortable about roasting them alive, placing the molluscs in boiling water kills them rapidly and they can also be kept in a deep freeze for a short time to reduce their metabolism severely before they are cooked.

Mark Zuckerberg became famous not only for Facebook, but also for his statement that killing animals oneself is better than willingly being ignorant of how we obtain the meat we buy from butchers or supermarkets [3]. For those that would like to follow Mr Zuckerberg's example, but cannot face the prospect of cutting the throat of a pig or a goat, killing snails of various kinds provides rather less of a challenge.   

[1] http://rwotton.blogspot.co.uk/2015/02/limpets-and-f1-cars.html

[2] M. S. Lovell (1867) The Edible Molluscs of Great Britain and Ireland with Recipes for cooking them. London, Reeve & Co.

[3] http://www.theguardian.com/environment/green-living-blog/2011/may/27/mark-zuckerberg-kill-animals-meat

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 https://natureinfocus.wordpress.com/category/seashore-creatures/limpets-seashore-creatures/page/2/). 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.

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.. ..by 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]

[2] http://www.cappelladegliscrovegni.it/index.php/en/

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

[4] Roger S. Wotton (2009) http://www.opticon1826.com/article/viewFile/opt.070906/54

[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.