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Living light

23rd March 2021

This blog is about a form of bioluminescence known variously as ‘sea sparkle’, ‘milky sea’ or more poetically ‘mareel’, which is a Shetlandic name meaning ‘sea fire’, (from Old Norse marr (“sea”) + eldr (“fire”). Also “miracle”, “morrali”, “glimro”)  

A near miss:

I feel greedy, wanting to see sea sparkle. The sea provides us already with seemingly inexhaustible inspiration and possibility; to want it to also put on a light show seems ungrateful.  I must admit though, since I first read descriptions of night-time glowing seas, I have wanted to see them for myself.

I got quite close once. I was ‘crewing’ for the first leg (Eastbourne to Falmouth), of a sailing trip that was going to cross the Bay of Biscay, carry on down to north Africa and eventually cross the Atlantic. The skipper was to pick up different crew for the various stages and on this first leg it was myself, a friend, my father-in-law, and a young vivacious eastern European girl whom none of us had met before called Lenka1.

This was to be my first time sailing at night and I was full of romantic expectation of seeing the mast ‘stir a sky full of stars’, the ‘loom’ of the lighthouses we would pass and maybe even sea sparkle. However, although we had good wind and a fast trip2 none of this happened. The sky was overcast, and the veiled moon and shore lights reflecting from the clouds prevented it from ever getting properly dark. There was not a star to be seen and certainly no glowing seas. With a strong north wind and a rough sea, it was also extremely cold and uncomfortable3.

We arrived in Falmouth tired and the three of us were relieved to climb into the warmth and comfort of a modern car and head for home.  

Lenka was staying on for the next leg and, after a day recovering, was to be joined by two new crew members for the trip across Biscay.  We swapped email addresses so we could keep track of how the rest of the journey went and said goodbye.

A couple of days later a wonderfully joyous email arrived in my inbox. High on tiredness and excitement, writing from the plane on the way back from Spain, Lenka described, in ecstatic broken English, how they had met not only bad weather and rough conditions but large areas of sea sparkle4. As the boat had ploughed into each glowing wave, cascades of glimmering sea spray had been fired back over the deck, drenching the crew, who, excited and laughing, had also begun to glow. Lenka described how the luminous water had run into their eyes, and mouths, picking them out and making them shine with sea fire.

As you might guess, I was sorry not to have been a part of this; to be aboard a boat sailing through a spectral sea with a maniacally laughing and glowing crew is something you will not get to do every day.

While I am unlikely to get the chance of experiencing sea sparkle in quite such dramatic circumstances I would still like to see it.  I have therefore made these few notes, partly out of curiosity and partly in the hope of increasing my (and anyone else who is interested) chances of seeing it in the future.

What is sea sparkle:

Nature has learned, through the guided play of evolution, to perform various tricks with light. Some of these modify light present in the environment, while with others generate ‘new’ light. The bright blue flash of a kingfisher, the shimmer of certain butterflies’ wings or the rays of the blue-rayed limpet5 are all examples of a phenomenon known as iridescence, in which the microscopic structure of the wing, feather or shell modifies the light falling on them, and causes them to shine and shimmer. Although iridescence generates no new light the effect can be surprisingly bright; catch the sun on the back of a kingfisher as it flies low over a river and you would think it was lit from within. 

Blue-rayed limpets – an example of iridescence in marine life.

Bioluminescent creatures on the other hand generate light and hence shine or glow in the dark. 

Instinctively, forgetting science for a moment, the ability to produce light seems to be somehow miraculous. There is something elemental about light.  It seems more than just another physical phenomenon. Light and its counterpoint darkness are a primeval pair of opposites.  ‘Let there be light’, the ‘light of reason’ and the ‘dark ages’, the ‘glimmer of consciousness’, the depiction of holy people as having haloes and the very word ‘enlightenment’, all contain light at their core. In children’s books as well, the ability to generate light is depicted as magical and firmly in the domain of wizards or supernatural beings, such as Harry Potter, Gandalf, Ged8 or ET. 

Such connotations seem to give light, and the ability to generate it, a mystical or even spiritual aspect6,7.

However, despite all this, being able to generate light through bioluminescence, is in fact very natural and commonplace. Many, many creatures, especially marine creatures, bioluminesce and it is thought that nature has reinvented bioluminescence fifty or so times during the course of evolution. The tree of life is, like a Christmas tree, decorated with many twinkling and flashing lights. 

The bioluminescent creature responsible for sea sparkle is a tiny single celled organism that drifts around the oceans as a component of plankton. It has the pretty Latin name ‘Noctiluca scintillans’, which translates as ‘sparkling night light’.

Undisturbed Noctiluca produces an extremely pale glow that is hard to see, but this changes if the water is disturbed by wave action or by someone walking or swimming. The cells then flash and sparkle with a blue-green light9 as a defence mechanism, to put predators off feeding, or to attract larger predators which will, in turn, feed on the predators of Noctiluca10

Swimming dolphins stimulate Noctiluca scintillans as they disturb the water11.

The mechanism by which bioluminescence is generated is chemical and is similar across many bioluminescent species. It involves an enzyme called Luciferase, and a light emitting compound called Luciferin12,13. In sea sparkle the Luciferase-Luciferin reaction is stimulated when the shape of the cell is distorted by the forces within the disturbed water. I have read that cells only sparkle at night and that even if you take a jar of sea water containing sea sparkle into a dark room it will not sparkle unless it is also night-time. It seems from this that although only a single cell Noctlluca must contain an internal clock, (but then you wonder if they also take account of the different lengths of night and day in winter and summer in which case, they also need to keep track of the time of year as well as the time of day). 

Finding sea sparkle

To be able to see sea sparkle it is necessary for Noctiluca to be present in large numbers; the conditions for this to occur therefore provide a guide for when it might be best to go hunting for it. 

These conditions include:

  • Warmth:  Noctiluca reproduces more readily in warm water, so looking after periods of warm weather might be a good idea.
  • Shelter:  Sheltered, calm bays are good hunting grounds as here the plankton stay near the surface of the water rather than becoming distributed throughout its depth. 
  • Onshore breeze: A gentle onshore breeze may also help as this will push the surface water containing the creatures toward the shore.

Even under these conditions I get the impression that the appearance of sea sparkle is quite erratic and unpredictable. There are, however, various internet groups dedicated to reporting sightings, including one dedicated to sightings around the Welsh coast14. Keeping an eye on such sites could significantly increase the chances of catching this elusive phenomenon.

If you go hunting, good luck!

Notes:

  1. Not her real name.
  2. Approx. 280 miles in 34 sailing hours (8.3 knots approx. average).
  3. It is one of the strange things about sailing that despite uncomfortable experiences like this it draws you back time and again.
  4. I do not know how large the areas Lenka sailed through were, but I have read that sea sparkle can cover thousands of square miles and be visible from space.
  5. There is a short blog I wrote about Blue-rayed limpets here.
  6. It seems to me a particularly charming aspect of bioluminescence that it is what might be considered more lowly creatures, such as glow worms, fireflies, jellyfish, and single celled plankton drifting on sea currents, that have the ability generate light, while the ‘higher’ mammals, including man, are denied it.
  7. This aspect was nicely brought out in the Disney film ‘Avatar’ in which the fantasy world of Pandora was lush with bioluminescent plants and creatures.
  8. Ged was a wizard in Ursula le Guinn’s excellent Earthsea Trilogy (which included the original school of wizardry on ‘Roke Island’).
  9. This shade of blue-green light is the best colour for penetrating sea water, (the colour of the rays of the blue rayed limpet is a similar shade, for the same reason).
  10. It is easy, when casually browsing on the internet, to get the impression that such interpretations are established facts – but other sources indicate that such ideas are just hypothesis and that research in many areas is still ongoing.
  11. Screen capture from full video at https://www.youtube.com/watch?v=bJcTWr8-mFo
  1. This is the subject of research inspired both by curiosity and the search for possible practical applications. The American university MIT are looking into the possibility of engineering bioluminescent plants to replace electrical lighting ( https://news.mit.edu/2017/engineers-create-nanobionic-plants-that-glow-1213 )
  2. ‘Lucifer’ is Latin for ‘bringer of light’.
  3. For example,  https://seasparkle.wales

Danger barnacles!

8th February 2021

Due to lock down I have been unable to get to the beach for a while and so this blog is based on some photographs I took on an earlier visit and some bookwork. It is about barnacles.

Barnacles (Latin name Cirripedia) are those tiny, ivory coloured, volcano shaped shells you see attached, often in large numbers, to rocks along the shore. Each is only a few millimetres across, but their numbers can be as the stars in the sky, colouring the rocks and becoming part of the landscape. I like them if that is not a silly thing to say. I am not quite sure why. They seem more like a form of rock than a form of life; hard, immovable, and apparently inert, yet as much a part of the shore as the sea and the sand.

Barnacles (and a few limpets) encrusting rocks in the intertidal zone.

Although they may appear featureless, get down on your knees and really look, perhaps with a magnifying glass, and you will see there is more to them than you might have thought.  Each shell is made up of several plates1 that form a small chamber, though often the plates are fused together and the joints hard to see. The chamber has a flat top which is closed by more plates making a pair of tiny gates. These gates meet along an intricate wiggly line which looks a little mysterious, almost as if the gates are sealed with a hieroglyph or magic symbol.  

But these gates do not need a spell to open them, just a covering of sea water. When the tide is out and the barnacle is above water the gates shut, providing protection from predators and preventing the creature inside drying out, but when submerged the gates open, allowing the barnacle to feed by extending a number of feathered legs called cirri which capture tiny particles of plankton suspended in the sea water. 

If you look carefully at different groups of barnacles up and down the shore you may find some that look subtly different; particularly the detailed shape of the plates and the line along which the gates meet. This might be because you are looking at a different species of barnacle, however barnacle identification is not easy, and you will need to look closely.

Two different species of barnacle. Left: Semibalanoides balanoides, Right: Chthalamus montagui (I think!) 

But be careful! Even as you crouch down to look you should know that you are potentially in danger and that although small and apparently lifeless, barnacles can be hazardous. It is a well documented fact that at least one fully grown man was trapped and held captive by barnacles, not for a few minutes, but for a full eight years. 

This man was Charles Darwin, the world-famous scientist and author of ‘The Origin of Species’ who, having found an unusual type of barnacle while voyaging on the Beagle thought he would spend ‘some months, perhaps a year’ 2 sorting out the then chaotic classification of the world’s barnacle species. Six years and many hundreds of pages of detailed scientific publication later he would write, to a friend (with still two years’ work to go):

“I am at work on the second vol. of the Cirripedia, of which creatures I am wonderfully tired: I hate a Barnacle as no man ever did before, not even a Sailor in a slow-sailing ship”.3,4

So, what is this creature that can engage such a brilliant and hardworking mind for eight years?  What exactly is a barnacle? 

Even before Darwin gave them his attention it had taken science quite a long time to decide what barnacles are and what class of animal they belong to. Maybe we can see why.  At a casual glance barnacles look like tiny limpets, which also have hard, roughly conical shells and, at the times we generally see them are stationary and appear rigidly attached to the rocks.  Barnacles and limpets however are completely different types of animal; limpets are molluscs, which are creatures like snails, that have soft unsegmented bodies, whereas barnacles have a segmented body and a hard exoskeleton. Even so barnacles were classified as a type of mollusc until it was discovered that they pass through two free-swimming larval stages5 before they permanently attach to the rocks. It was the observation of these larval stages that led to the correct classification of barnacles in 1834, as belonging to Crustacea, the same grouping as crabs, shrimps and lobsters.    

There are two main categories of barnacle, the type we have been talking about, which attach directly to the rocks and are known as sessile barnacles and a type that attach via a stalk, which are known as pedunculate barnacles. There are over a thousand species of barnacle worldwide but around the UK we have just two or three species of pedunculate barnacles, which are usually found washed ashore attached to floating driftwood or plastics and, depending on whether you count invasive species or not, six or nine species of sessile barnacle.  However, differentiating even such small numbers of species can be tricky.  In the words of Charles Darwin again:

Whoever attempts to make out from external characters alone, without disarticulating the valves [Darwin called the shell plates valves], the species, (even those inhabiting one very confined region, for instance the shores of Great Britain) will almost certainly fall into many errors”6

The difficulty seems to arise because there is a large variation in the appearance of individual barnacles, even within one species. Books such as ‘A Student’s Guide to the Seashore’7 offer a step through guide to barnacle identification, but as alluded to by Darwin, differentiating between some species requires scraping the barnacle off the rock and dismantling it. Personally, I think I would rather live with a little ambiguity in my identifications.  

If we think classifying barnacles as molluscs was something of a scientific blunder it is as nothing to what was believed in the middle ages about a type of pedunculate barnacle known as a goose barnacle.  This type of barnacle, which was found washed up on British shores attached to driftwood, was thought to be the embryo of a black and white goose known as a barnacle goose. Because this goose only winters in the UK it was never seen to breed and as migration was not understood at that time an explanation for its seasonal appearance was lacking.  The shape and colour of the floating goose barnacle looks, if you have a good imagination, somewhat like the beak, head, and neck of the goose and so the one was assumed to be the embryo of the other.  The full supposed life cycle involved a barnacle goose tree (remember the barnacles were always found attached to wood), on which the goose barnacles grew and from which the geese hatched.

One form of the wonderful barnacle goose tree8.

There is an Anglo Saxon riddle that accompanies this story:

My beak was close fettered, the currents of ocean,
running cold beneath me. There I grew in the sea,
my body close to the moving wood.
I was all alive when I came from the water,
clad all in black, but a part of me white.
When living, the air lifted me up,
the wind from the wave, and bore me afar,
up over the seal’s bath. Tell me my name
9.

I have to say, I find this an attractive story and sometimes wonder if it might not have been fun to have lived in less scientifically constrained times, when one could be free to entertain poetic ideas like geese hatching from barnacle trees. But then maybe there is a poetry of a different and more powerful sort in the image of a man working patiently for eight years to understand these tiny creatures, while all the time devising the theory that would explain the growth, not of the barnacle tree, but of another tree, the evolutionary tree of life, among the branches of which not only barnacles and geese but man and all other creatures would be shown to have their place.

Notes:

  1. Some UK species of barnacle have four plates, and some have six.
  2. Letter to: J. D. Hooker   [2 October 1846]
  3. Letter to: W. D. Fox, [24 October 1852]
  4. This and other wonderful excerpts from Darwin’s letters at: https://www.darwinproject.ac.uk/darwins-bad-days
  5. Observations of the ‘naupliar’ and nonfeeding ‘cypris’ stages of the barnacle’s life cycle were published in 1830 by the British military surgeon and marine biologist John Vaughan Thompson.
  6. From:  A Monograph on the Cirripedia, by Charles Darwin, London: Ray Society, 1854.
  7. ‘A Student’s Guide to the Seashore.’ J. D. Fish & S. Fish (Third Edition) (301-311)
  8. From Topographia Hibernica British Library MS 13 B VIII Ray Oaks, CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons)
  9. Anglo-Saxon Riddles of the Exeter Book  (1963) translated by Paull Franklin Baum (Creative Commons Attribution-ShareAlike License)

Searching the shore

11th January 2021

I am no biologist, and I don’t really know very much about shore life.  Before retiring and moving to be near the sea I worked in physics and engineering.  The attractions of the sea were for me, like most people I would think, a mixture of fresh air, the simple pleasures of sun, sand and sea on skin and the novelty of a different environment. But the coast has also always inspired. I used to walk along the shore and use the sea and sand to spark thoughts about physics. Actual physics, such as wondering how sand ripples form or more esoteric metaphysical thoughts, inspired by the sea, about the universe or time and space. Biology was never my thing, a bit too squishy and potentially messy for my liking and, I thought, less fundamental and therefore intrinsically less interesting than the big questions of physics. 

Bird watching was the nearest I came to an interest in life sciences. I had often thought that once retired and settled in, I would look for some ornithologically themed volunteer work. I imagined myself monitoring bird numbers along some stretch of wild Pembrokeshire coast. Motivation for a regular walk and a chance to feel like I was doing something useful in the face of the constant soul-destroying news of climate change, pollution, habitat loss and declining wildlife.       

It was my son who noticed the online advert for volunteers for Living Seas Wales (https://livingseas.wales/ )   and passed it to me. Not birds, but the life of the seashore. Recording what is present, but also looking for invasive species or species indicative of climate change.  

The novelty intuitively appealed. The chance to learn something new. Not just new, but quite different. The sea, an unknown alien world to most of us, is particularly good at firing our imaginations and I enjoyed the thought of immersing myself in this new subject. I made contact and after a pleasantly small amount of admin and some online training, was ready to go. 

Since discovering it a few years ago I have greatly enjoyed the area around Dinas Island on the north Pembrokeshire coast. The walk around the head itself is beautiful and dramatic with views out into Cardigan bay and across to North Wales. There is even a small sea stack which, in the spring and summer, hosts colonies of beautiful, raucous seabirds including razorbills and guillemots.

Razorbills and guillemots on Needle Rock, Dinas Island

It was maybe natural then that I would choose a bay near the Head for my first shore search.

Picking a pleasant day, I arrived a little before low tide. It was easy this first time. I knew nothing and so everything was new. I thought the easiest thing might be just to take photographs and identify what I found back at home with books and the internet to hand. I walked over the sand, heading to the rocks that form one side of the bay, photographing the different seaweeds that were either growing on rocks or cast up on the sand as I went. 

I like the early stages of getting into a new subject. It reminds me of looking out onto a field of newly fallen snow.  You have no preconceptions or mental clutter and are free to wander where you will, think what you like and ask whatever questions come to mind. I remember wondering whether seashore life is as seasonal as life on the land and whether the types of rocks, or how exposed a shore is, has much effect on what will be found there. I also had more specific questions such as whether those little fish you sometimes find in rock pools choose to live there or just get stranded as the tide goes out and if a rock pool is simply a visible bit of the undersea habitat that lies all around or a fundamentally different and unique eco-system.

Arriving at the east end of the bay I chose a moderately sized, attractive looking rock pool and knelt for a closer look.

Rockpool

It is a cliché I know, but rock pools do look like gardens. Some look like flower gardens, full of life and colour, others are more like Japanese Zen gardens, austere arrangements of rock and light and shade. This one was of the first type, a play of weeds of different shapes and colours; greens and reddy-browns, flat, and feathery, with the rock basin below the water line covered in that pale pink growth you sometimes see; a type of under-water lichen perhaps?

There were a number of those sea anemones that look, when they are closed, like blobs of red jelly, as well as shells of various sorts, some I recognised as limpets but others I was not sure about. I took photos of all these before spotting something more unusual; a broad piece of brown seaweed covered in a fine geometric pattern. I had no idea what this was. More photographs.

I was just about to move on when I became aware of a small patch of pale star-like growth, partially hidden among the weed on the bottom of the pool. As my eyes tuned in, I realized there was quite a lot of it, perhaps it was another type of anemone.

A quick look around, followed by a cup of coffee sat on a rock and a short, shouted conversation about the pleasantness of the morning with a fisherman setting out to pick up lobster pots and it was time to go. It had been good. There is something about going to a place with a sense of purpose rather than just strolling along looking at the view. You engage with things more deeply, people come up and talk to you, interested in what you are doing.

My lasting impression was just how much life there had been. Fifteen species1 within a few square yards, some of which I had never seen before and had not known existed. Seashore life is not cosy or cute, but it is beautiful and wonderfully alien. You might as well be exploring life on other planets, Star Trek style, as delving into rock pools. Getting to know the shore is bringing home to me that Life is at least as great a mystery as the abstract questions of physics and of course, you only have to look up and the birds are there as well.

A few of the species described above (tentative ID):

  1. As of now (January 2021) this total is now 28. I have an on-going photo-record at: https://jonjamesart.com/shore-search/

Philosophy of Mind

4th January 2021

I recently completed an Oxford University short course on Philosophy of Mind. This is an area I have interested in (or maybe I should say tormented by) for a long time.

I would like to write some more on this at some point, but for the moment I have just copied the final essay of the course below. Probably it wont be of interest to anyone, but I feel it might as well go here as anywhere, or nowhere.

Can one reasonably be a dualist in this day and age?

Before attempting to answer this question, it is important to clarify what we are referring to by the term ‘dualism’ and to delineate the scope of what we are wanting dualism to be a reasonable explanation of.  For example, we might construct an argument that makes a reasonable case for dualism as an explanation of those subjective conscious experiences (such as seeing a colour), known as qualia, but that fails to account for the possibility of mental states interacting with and controlling the physical, as is required for mental causation and our apparent capacity for exercising free-will.  Whether we consider the position of the dualist ‘reasonable’ may depend on whether we consider these phenomena real and in need of explanation.

We assume here that qualia are real and so reject forms of eliminativism that conclude otherwise. Further, while we look for reasonable explanations of qualia, we leave aside, initially, questions of mental causation. In this way we allow (though do not necessarily endorse) the theory of epiphenomenalism, which holds that mental phenomena, though real, have no causal agency. This is a significant step as it removes the need to address questions of how the mental might influence the physical and whether physical events can have non-physical causes, a possibility denied if, as is often stated, the universe is ‘causally closed’.

Dualism comes in two flavours; substance dualism, as most famously expounded by Rene Descartes in 1641 and property dualism. Substance dualism suggests that there are two fundamentally distinct substances in the world; the material substance, as explored and to some extent understood by the science of physics and a mind substance, hitherto unknown, other than, it would be argued, through subjective experience.  Property dualism on the other hand holds that there is only one substance; the material substance of physics, of which mental phenomena are a property. We take the dualism of the title question to refer to either of these flavours. 

It might seem from the above that one or other form of dualism must be true.   Under the proposition that qualia exist and as they appear not to be accounted for by our current scientific understanding, they must surely be due to either a new undiscovered mind substance (substance dualism) or a new undiscovered property of material substance (property dualism).  

Contra to this impression however there are philosophies of mind that are classified as neither substance nor property dualism. For example, reductive physicalist theories are generally considered distinct from property dualist theories, even though both propose the existence of only one type of substance: physical matter.

Such distinctions seem to depend on how we define, label and group properties.  Property dualism holds that mental properties are ‘ontologically distinct’ from, or somehow ‘over and above’ physical properties, whereas reductive physicalist theories hold that all properties, including those that account for mental phenomena, are physical.   

The interpretation of the word ‘physical’ seems to be pivotal here. What do we mean by ‘physical’? Physical seems, generally, to be taken to mean ‘as known to science’ or more specifically physics. But physics is an evolving discipline, so ‘as known to physics’ is a time dependent category. If we take the physical to be defined with respect to the current state of physics then reductive physicalism appears to be false, unless we think consciousness can be explained by current physics, in which case we might reasonably ask what combination of currently accepted physical properties (velocity, mass, charge, etc) accounts for my subjective experience of the colour red. If on the other hand we take physics to refer to some ideal future body of knowledge then reductive physicalism might be considered trivially true, since it might be expected physics will expand to include the phenomenon of consciousness in time. This difficulty around the definition of ‘physical’ is expressed in similar terms by Hempel’s dilemma (Hempel 1969) and is a problem in delineating physicalist theories of mind.

Taking the definition of ‘the physical’ as ‘that known to current physics’ as the most reasonable option we suggest the following three propositions.

  1. that the physical domain is defined as that described by today’s physics
  2. that qualia are real
  3. that current physics is unable to explain qualia

These propositions seem to entail property dualism and so, if we consider them reasonable, being a dualist, of one sort or another, must also be reasonable.

So far, we have deliberately made no reference to the need to account for mental causation. Such a position allows epiphenomenalism and coincides with David Chalmers Type-E Dualism, (Chalmers 2002). If we reject epiphenomenalism and require the mental to have causal agency, we must consider how mental events can affect physical events and must allow that such considerations may change our judgement as to whether or not dualism is reasonable.

Considering it desirable to not multiply entities unnecessarily, (and given natural constraints on the scope of this essay), we choose to concentrate on the possibility that mental causation can be accounted for using properties of the material world, i.e. we investigate property dualism. 

The main difficulty with ascribing the mental to properties of physical matter is that we think we know how physical matter works.  Working from the microphysical level we assume an upward causation, from the small to the large (from atoms to molecules to materials etc) thereby achieving, at least in principle, an explanation of the entire universe. Such upward causation seems to leave no room for the physical to be affected by some unknown mental process.  Opposed to this conclusion however is the idea that there may be gaps in this causal chain which are not readily apparent and at which other effects may emerge.

The two most cited candidates for such gaps are the quantum realm or the realm of the complex. The second of these gives rise to the idea of emergentism which holds that new properties arise when objects attain a certain complexity. At and above this complexity threshold the arrow of causation may be reversed, so that the behaviour of the whole can no longer, even in principle, be derived from an understanding of the parts. While it seems, many physicists would dispute the possibility of such emergent properties, other notable physicists offer it some support.  For example, the physicist and cosmologist Paul Davies discusses (Davies 2004) how there are arguments from within physics that leave the way open for downward causation at certain levels of complexity: 

“The numerical results of the previous section may be used to estimate the threshold of complexity beyond which there is no conflict between the causal determinism of the microscopic components and the existence of emergent laws or organizing principles at a higher level.”

The relevant complexity is calculated via a theoretical computability argument and he suggests, within the same article, that:

“… the key molecules for life—nucleic acids and proteins— become biologically efficacious at just about the threshold predicted by the Landauer-Wheeler limit, corresponding to the onset of emergent behaviour”

The thrust of the article is not to prove that emergent properties or downward causation exist, but to loosen fundamental objections to their so doing.

The second candidate for downward causation is the quantum realm.  As is well known and discussed in Chalmers (Chalmers 2002), observation by a conscious observer has long been mooted as a possible cause of ‘wave function collapse’, in which the smoothly evolving wave function, which allows a superposition of multiple states, collapses to a single measured reality.  More recently ideas of ‘de-coherence’ seem to be lessening the need for the conscious observer in this process.  However, it has more recently been suggested that phenomena such as quantum entangled states, do in fact exhibit emergent properties and allow downward causation. In their paper ‘Event ontology in quantum mechanics and downward causation ‘ Gambini and Pullin (2016) conclude;        

“We show that several interpretations of quantum mechanics admit an ontology of objects and events. This ontology reduces the breach between mind and matter”

“Basically, downward causation is present when the disposition of the whole to behave in a certain way cannot be predicted from the dispositions of the parts. The event ontology of quantum mechanics allow us to show that systems in entangled states present emergent new properties and downward causation.”

Reading Davies’ article or, more so, the quantum article cited above, brings to the fore a difficulty with our attempt to establish the reasonableness or otherwise of dualism. In considering subjects such as quantum physics and downward causation we are quickly drawn into highly technical areas of a very specialist nature. If we do not have the specialist knowledge (specialist even within the discipline of physics) to follow and critically evaluate such arguments how shall we proceed? 

We are forced to the somewhat unsatisfactory conclusion that if reasonable and knowledgeable men and women can take particular positions regarding such technical questions, we are beholden to at least allow that holding such opinions is reasonable. It follows that we should be free to consider the possibility of downward causation, emergent properties and property dualism as at least reasonable propositions, even when including mental causation within our ontology.

Beenakker, C. (2007) ‘Hempel’s Dilemma and the Physics of Computation,’ Knowledge in Ferment: Dilemmas in Science, Scholarship and Society (Leiden University Press)

Chalmers, D.  J. (2002) ‘Consciousness and its Place in Nature,’ Published in (D. Chalmers, ed) Philosophy of Mind: Classical and Contemporary Readings (Oxford 2002).

Davies, P. (2004) ‘Emergent biological principles and the computational properties of the universe,’ Complexity. 10. 11-15. 10.1002/cplx.20059.

Gambini, R. and Pullin, J. (2016) ‘Event ontology in quantum mechanics and downward causation,’ International Journal of quantum foundations 2, 89, 2016

Hempel, C. (1969) ‘Reduction: Ontological and Linguistic Facets’, in S. Morgenbesser, et al. (eds.), Essays in Honor of Ernest Nagel, New York: St Martin’s Press.

Hunting Patella pellucida

30th October 2020

They were there, on the first piece of kelp we looked at. On the side facing down into the sea, just where the fronds join the stipe. A little cluster of five, each no bigger than a fingernail.

It had almost been too easy. But, looking back the clues had been there a few weeks before when we had found, amongst the usual limpets and topshells, some small soft-brown domes with barely visible pale stripes radiating from one end. Apparently a type of limpet, but not looking like any of the textbook illustrations. We had wondered then if they were old and worn blue-rayed limpet shells.

Checking online and in our favourite textbook1 it appeared that blue-rayed limpets often feed on a species of kelp known as Laminaria digitata; a large brown fingered seaweed which grows on rocky shores and is usually only accessible at the lowest of low tides. I knew from sailing that these tides, ‘spring tides’ typically occur twice a month, near full and new moons, when the alignment of the earth moon and sun produces maximum gravitational pull. Looking at our local tide tables, we noted the date and time of the next such tide.  

But where to look? Laminaria digitata grows by clinging to rocks. Much of the north coast of Pembrokeshire is rocky, but as I had recently found this seaweed washed up on a beach near Dinas Island, while doing a shore search for Living Seas Wales (https://livingseas.wales/), we chose this as our hunting ground.

Arriving shortly before low water and climbing over rocks still wet from the receding tide, we made our way to the sea and turned over the first piece of kelp we saw. And there they were, smaller than expected, but unmistakable.  Tiny translucent fawn-green domes with piecing radiating blue-green lines; the living version of the pale brown shells we had found previously.  The tide was already on the turn and balancing on slippery rocks we took what photographs we could and retreated.

Blue-rayed limpets (Patella pellucida) feeding on kelp.

Looking at the photographs now the lines are striking. From amongst the dark softness of the kelp, where all is organic asymmetry, these draftsmen-drawn lines shine out like decals on tiny spaceships. Their iridescence arcs across the shell domes, with apparently little regard for the assumed concentric or radial growth patterns and symmetries. They are the colour of kingfishers caught in slanting light against the greens and browns of a river.  

References:

  1. A Student’s Guide to the Seashore. J. D. Fish & S. Fish (Third Edition)

Notes:

  1. Patella pellucida is the Latin name of the blue-rayed limpet. ‘Patella’ and ‘Pellucid’ are Latin words meaning ‘little dish’ and ‘lucid or clear’ or ‘to shine’ respectively.
  2. The iridescence of these limpets is an example of ‘structured light’, in which colour is caused, not by the usual method of pigmentation, but by geometric arrangements of microscopic structural elements that cause interference and filtering of certain wavelengths of light.  The example of blue-rayed limpets is unusual because this effect is created by mineral rather than organic compounds as is the case in creatures such as kingfishers or butterflies.
  3. There is a scientific study into the Blue-rayed limpet by the Massachusetts Institute of Technology (MIT): The paper is here: (http://web.mit.edu/cortiz/www/LingLiPhotonic.pdf) and a less technical article here: https://news.mit.edu/2015/optical-structures-in-limpet-shell-0226. Some of the more accessible points are:
    1. The iridescence is produced by layers within the thickness of the shell rather than on the surface.
    2. The blue of the rays is the optimum shade for penetrating water.
    3. The changes in shell structure needed to cause iridescence do not weaken the shell.
    4. It is thought that the evolutionary advantage of the iridescence of blue-rayed limpets is that it mimics colourful species of toxic sea slugs (nudibranchs), such as Polycera elegans.  

Additional Figures: