‘Mary’s Room’: A Thought Experiment

Posted by Keith Tidman

Can we fully understand the world through thought and language—or do we only really understand it through experience? And if only through experience, can we truly communicate with one another on every level? These were some of the questions which lay behind a famous thought experiment of 1982:

A brilliant neurophysiologist, Mary, knows all there is to know about her academic specialty, the science of vision: the physics, biology, chemistry, physiology, and neuroscience. Also how we see colour.

There’s a catch, however: Mary has lived her entire life in a totally black-and-white room, watching a black-and-white screen, and reading black-and-white books. An entirely monochromatic existence. Then, unexpectedly, her screen reveals a bright-red tomato.

What was it like for Mary to experience colour for the first time? Or as the Australian philosopher Frank Jackson asked, who originated this thought experiment, ‘Will [Mary] learn anything or not?’ *

Jackson’s original takeaway from his scenario was that Mary’s first-time experience of red amounted to new knowledge—despite her comprehensive scientific knowledge in the field of colour vision. Jackson believed at the time that colour perception cannot entirely be understood without a person visually experiencing colour.

However, not everyone agreed. Some proposed that Mary’s knowledge, in the absence of first-hand experience, was at best only ever going to be partial, never complete. Indeed, renowned philosopher Thomas Nagel, of ‘what is it like to be a bat’ fame, was in the camp of those who argue that some information can only be understood subjectively.

Yet, Mary's complete acquaintance with the science of vision might well be all there is to understanding the formation of knowledge about colour perception. Philosopher and neurobiologist Owen Flanagan was on-board, concluding that seeing red is a physical occurrence. As he put it, 'Mary knows everything about colour vision that can be expressed in the vocabularies of a complete physics, chemistry, and neuroscience.

Mary would not have learned anything new, then, when the bright-red tomato popped up on her screen. Through the completeness of her knowledge of the science of colour vision, she already fully knew what her exposure to the red tomato would entail by way of sensations. No qualities of the experience were unknowable. The key is in how the brain gives rise to subjective knowledge and experience.

The matter boils down to whether there are nonphysical, qualitative sensations—like colour, taste, smell, feeling, and emotion—that require experience in order for us to become fully familiar with them. Are there limits to our comprehension of something we don’t actually experience? If so, Mary did learn something new by seeing red for the first time.

A few years after Frank Jackson first presented the ‘Mary’s room’ thought experiment, he changed his mind. After considering opposing viewpoints, he came to believe that there was nothing apart from redness’s physical description, of which Mary was fully aware. This time, he concluded that first-hand experiences, too, are scientifically objective, fully measurable events in the brain and thus knowable by someone with Mary’s comprehension and expertise.

This switching of his original position was prompted, in part, by American philosopher and cognitive scientist Daniel Dennett. Dennett asserted that if Mary indeed knew ‘absolutely everything about colour’, as Jackson’s thought experiment presumes, by definition her all-encompassing knowledge would include the science behind people’s ability to comprehend the actual sensation of colour.

To these points, Mary’s factual expertise in the science of colour experience—and the experience’s equivalence and measurability in the brain—appears sufficient to conclude she already knew what red would look like. The experience of red was part of her comprehension of human cognitive functions. Not just with regard to colour, but also to the full array of human mental states: for instance, pain, sweetness, coldness, exhilaration, tedium—ad infinitum.

As Jackson ultimately concluded, the gist is that, given the special particulars of the thought experiment—Mary acquired ‘all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like red and blue’—Mary did not acquire new information upon first seeing the red tomato. She didn’t learn anything. Her awareness of redness was already complete.

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* Frank Jackson, 'Epiphenomenal Qualia', Philosophical Quarterly, 32, April 1982.

The Afterlife: What Do We Imagine?

Posted by Keith Tidman

‘The real question of life after death isn’t whether 

or not it exists, but even if it does, what 

problem this really solves’

— Wittgenstein, Tractatus Logico-Philosophicus, 1921

Our mortality, and how we might transcend it, is one of humanity’s central preoccupations since prehistory. One much-pondered possibility is that of an afterlife. This would potentially serve a variety of purposes: to buttress fraught quests for life’s meaning and purpose; to dull unpleasant visions of what happens to us physically upon death; to switch out fear of the void of nothingness with hope and expectation; and, to the point here, to claim continuity of existence through a mysterious hereafter thought to defy and supplant corporeal mortality.

And so, the afterlife, in one form or another, has continued to garner considerable support to the present. An Ipsos/Reuters poll in 2011 of the populations of twenty-three countries found that a little over half believe in an afterlife, with a wide range of outcomes correlated with how faith-based or secular a country is considered. The Pew Center’s Religious Landscape Study polling found, in 2014, that almost three-fourths of people seem to believe in heaven and more than half said that they believed in hell. The findings cut across most religions. Separately, research has found that some one-third of atheists and agnostics believe in an afterlife — one imagined to include ‘some sort of conscious existence’, as the survey put it. (This was the Austin Institute for the Study of Family and Culture, 2014.) 

Other research has corroberated these survey results. Researchers based at Britain's Oxford University in 2011 examined forty related studies conducted over the course of three years by a range of social-science and other specialists (including anthropologists, psychologists, philosophers, and theologians) in twenty countries and different cultures. The studies revealed an instinctive predisposition among people to an afterlife — whether of a soul or a spirit or just an aspect of the mind that continues after bodily death.

My aim here is not to exhaustively review all possible variants of an afterlife subscribed to around the world, like reincarnation — an impracticality for the essay. However, many beliefs in a spiritual afterlife, or continuation of consciousness, point to the concept of dualism, entailing a separation of mind and body. As René Descartes explained back in the 17th century:

‘There is a great difference between the mind and the body, inasmuch as the body is by its very nature always divisible, whereas the mind is clearly indivisible. For when I consider the mind, or myself insofar as I am only a thinking thing, I cannot distinguish any parts within myself. . . . By contrast, there is no corporeal or extended thing that I can think of which in my thought I cannot easily divide into parts. . . . This one argument would be enough to show me that the mind is completely different than the body’ (Sixth Meditation, 1641).

However, in the context of modern research, I believe that one may reasonably ask the following: Are the mind and body really two completely different things? Or are the mind and the body indistinct — the mind reducible to the brain, where the brain and mind are integral, inseparable, and necessitating each other? Mounting evidence points to consciousness and the mind as the product of neurophysiological activity. As to what’s going on when people think and experience, many neuroscientists favour the notion that the mind — consciousness and thought — is entirely reducible to brain activity, a concept sometimes variously referred to as physicalism, materialism, or monism. But the idea is that, in short, for every ‘mind state’ there is a corresponding ‘brain state’, a theory for which evidence is growing apace.

The mind and brain are today often considered, therefore, not separate substances. They are viewed as functionally indistinguishable parts of the whole. There seems, consequently, not to be broad conviction in mind-body dualism. Contrary to Cartesian dualism, the brain, from which thought comes, is physically divisible according to hemispheres, regions, and lobes — the brain’s architecture; by extension, the mind is likewise divisible — the mind’s architecture. What happens to the brain physically (from medical or other tangible influences) affects the mind. Consciousness arises from the entirety of the brain. A brain — a consciousness — that remarkably is conscious of itself, demonstrably curious and driven to contemplate its origins, its future, its purpose, and its place in the universe.

The contemporary American neuroscientist, Michael Gazzaniga, has described the dynamics of such consciousness in this manner:

‘It is as if our mind is a bubbling pot of water. . . . The top bubble ultimately bursts into an idea, only to be replaced by more bubbles. The surface is forever energized with activity, endless activity, until the bubbles go to sleep. The arrow of time stitches it all together as each bubble comes up for its moment. Consider that maybe consciousness can be understood only as the brain’s bubbles, each with its own hardware to close the gap, getting its moment’. (The Consciousness Instinct, 2018)

Moreover, an immaterial mind and a material world (such as the brain in the body), as dualism typically frames reality, would be incapable of acting upon each other: what’s been dubbed the ‘interaction problem’. Therefore the physicalist model — strengthened by research in fields like neurophysiology, which quicken to acquire ever-deeper learning — has, arguably, superseded the dualist model.

People’s understanding that, of course, they will die one day, has spurred search for spiritual continuation to earthbound life. Apprehension motivates. The yearn for purpose motivates. People have thus sought evidence, empirical or faith-based or other, to underprop their hope for otherworldly survival. However, modern reality as to the material, naturalistic basis of the mind may prove an injurious blow to notions of an out-of-body afterlife. After all, if we are our bodies and our bodies are us, death must end hope for survival of the mind. As David Hume graphically described our circumstances in Of the Immortality of the Soul (1755), our ‘common dissolution in death’. That some people are nonetheless prone to evoke dualistic spectral spirits — stretching from disembodied consciousness to immortal souls — that provide pretext in desirously thwarting the interruption of life doesn’t change the finality of existence. 

And so, my conclusion is that perhaps we’d be better served to find ingredients for an ‘afterlife’ in what we leave by way of influences, however ordinary and humble, upon others’ welfare. That is, a legacy recollected by those who live on beyond us, in its ideal a benevolent stamp upon the present and the future. This earthbound, palpable notion of what survives us goes to answer Wittgenstein’s challenge we started with, regarding ‘what problem’ an afterlife ‘solves’, for in this sense it solves the riddle of what, realistically, anyone might hope for.

‘Purposeful Living’ Through Grief

Rainy Night In The City, by Alina Madan. Poster: Giclee Print

Posted by Lina Ufimtseva

Grief is like a rude neighbour in the night, knocking at your mind’s door at all kinds of inopportune moments.  Hush, you want to tell it, go away, let me sleep.  But not only is grief rude in its all-encompassing demands for attention, it also is disobedient, and stubbornly stays.  Often, for years.

I am stirring a pot of soup on the stove, and I switch it off.  The boiling liquid quickly settles, and the rolling of the surface stops.  ‘Just like my mother's blood,’ I think instinctively.  Her blood stopped moving, too. ‘Just so,’ I think, ‘a loved one's life can slip away, unceremoniously.’ And so, in the sudden memory which the soup brings back, grief stands rudely knocking.  Go away, go away.

Time allows for the body to regenerate and to heal, provided it is not put under more stress.  Years later, one may feel the strain in a joint from an old injury, but it will often be no more than a lingering nuisance.  Grief, on the other hand, can hit one like a train, no matter how much time has passed since tragedy struck. Why is emotional pain more difficult to bear than physical pain? 

The brain uses a single neural system to detect and feel pain.  The anterior insula cortex and the anterior cingulate cortex are responsible for detecting pain, regardless whether it is of a physical or emotional nature.  Even painkillers may numb emotional pain temporarily.  But they don’t help in healing.

This begs the question, why does emotional pain not heal as if it were physical?

Upon asking how a mother’s labour went, a woman may underplay her experience and reply that it was ‘painful’ or ‘a lot of pressure’.  Yet those mothers who lay in agony giving birth will voluntarily unleash the same process upon their bodies again and again.  Physical pain lingers only as an awareness that it was indeed at one time painful. 

Grief, however, has the unique ability to reiterate itself at the most seemingly random moments.  Therein lies a clue.  If we want physical pain to leave our bodies—assuming that, as it usually does,-- it affects only a certain limb or area of the body—we may use a crutch to prevent too much strain, say, on a leg.  But how does one rest from grief?

Generally one does not.

Our brains process the pain of grief in a non-linear manner.  Physical trauma leaves scars—smooth scars.  Emotional pain creates what I would call neural scabs of sorts that can be—and often will be—picked at, voluntarily or not.

The psychologist Thomas Crook has noted:

‘Indeed, when brain imaging studies are done on people who are grieving, increased activity is seen along a broad network of neurons.  These link areas associated not only with mood but also with memory, perception, conceptualization, and even the regulation of the heart, the digestive system, and other organs.  This shows the pervasive impact loss or even disappointment can have.’

Grief affects the neural pathways in a far more pervasive and ineluctable or ineludible manner than physical pain.  Emotional pain, like a scab, can very easily get picked by a casual scratch of an old memory, and the blood of grief starts pouring again.

Those who have been severely distraught by their circumstances often come to the conclusion that the greater meaning in life is not seeking happiness and hedonism, but in creating a purposeful living.  The word choice here: ‘a purposeful living’ rather than ‘a purposeful life’, is in itself deliberate.  Meaning is not stagnant.  One cannot create a purposeful life and leave it at that.  Purpose must continue to be lived out, to be striven for, to continue in some kind of endeavour. 

Purpose without struggle often loses its meaning.  In this light, grief can be given a purpose.  Severe emotional pain can be the catalyst to revaluate one’s values, choices, and path in life.  It can be one’s very own personal as well as professional spring board. 

Do you wish to leap into the bounds of further despair?  Go ahead, and grief will get you there.  Do you wish to see an armour around yourself unveiled?  Go ahead, and grief can give you the thickest skin and the thinnest heart you ever imagined.

Grief can and will redefine who you thought you were.  Can you hear it knocking?

Hearts and Minds: The Mystery of Consciousness

By Mary Monro

Despite the best efforts of scientists and philosophers over the centuries, no mechanism has been discovered that indicates how consciousness emerges in the brain. Descartes famously thought the soul resided in the pineal gland - but that was mainly because he couldn't think of any other purpose for it (It actually produces melatonin and guides sleeping patterns). But, 400 years on, perhaps we still need to think again about where consciousness might reside.

In recent years there has been a surge of interest in the gut brain, with its hundred million neurons and its freight of microbes, that influences every aspect of our being including mood and memory. If the gut might now be considered a possible source of consciousness what about other candidates?

After all, “Primary consciousness arises when cognitive processes are accompanied by perceptual, sensory and emotional experience” as Fritjof Capra and Pier Luigi Luisi put it in their book The Systems View of Life: A Unifying Vision (2014).  Reflective or higher-order consciousness includes self-awareness and anticipation.

There is another intelligent, organising, feeling, planning, responsive, communicating organ inside us – a body-wide-web lining our blood vessels. Vascular endothelium cells (VE for short) line every vessel from the heart to the smallest capillary, reaching into every part of the body. Vascular endothelium is the interface between the blood and the tissues, deciding what goes where through a combination of electrical, kinetic, mechanical and chemical signalling.

Laid out, the VE in a human body would be the size of a rugby pitch yet it weighs only one kilogram. Far from being simply wallpaper, recent research has shown it to be a lead actor in the management of the body, including the brain. It is believed that each of the sixty trillion cells of the VE is unique, each one exquisitely adapted to meet the needs of its immediate environment, whether that is in the deeply oxygen deprived depths of the kidney or the highly oxygenated gas exchange surface of the lung. William Aird, in a scholarly paper in 2007, describes vascular endothelium as 'a powerful organising principle in health and disease'.

The blood-brain barrier (usually abbreviated to BBB) protects the brain from molecules and cells in the blood that might damage neural tissue. The vascular endothelium forms the interface but it was previously thought to be a passive sieve, controlled by neurons. The BBB has now been renamed the ‘neuro-vascular unit’ as it has become clear that neural cells, pericytes (that back the endothelial cells) and the vascular endothelial cells all actively take part in managing this critical barrier. It is not known which of them is in charge.

Other researchers have sought to apply the Turing Test to the VE in the brain – the Turing Test being an evaluation of whether an information processing system is capable of intelligent, autonomous thought. Christopher Moore and Rosa Cao, argue that blood is drawn to particular areas of the brain by the VE, in advance of metabolic demand, where it stimulates and modulates neuronal function. So the brain is responder rather than activator. Who is doing the thinking? Is the body-wide-web (including the heart and its assistant the blood) gathering information from the body and the external environment to tell the brain what to do? How does it make decisions? What does this imply for consciousness?

In fact, long ago, Aristotle asserted that the vascular architecture in the embryo functions as a frame or model that shapes the body structure of the growing organism. Recent research bears this out, with the VE instructing and regulating organ differentiation and tissue remodelling, from the embryo to post-natal life.  The VE cells form before there is a heart and it is fluid flow that drives endothelial stem cells to trigger the development of the heart tube, vessels and blood cells. There is no brain, only a neural tube, at this stage.

Recent research has shown that blood vessels can direct the development of nerves or vice versa or they can each develop independently. So, embryologically, there is a case for saying that the VE is a decision making executive.

All this recalls a founding principle of osteopathy – which is that ‘the rule of the artery is supreme’.  This is a poetic, 19th century way of saying that disturbance to blood flow is at the root of disease. In his autobiography, published in 1908, Andrew Still remarks: ‘in the year 1874 I proclaimed that a disturbed artery marked the beginning to an hour and a minute when disease began to sow its seeds of destruction in the human body’.

Now, almost a century and a half on, we find that ‘endothelial activity is crucial to many if not all disease processes’, as K. S. Ramcharan put it in a recent paper entitled ‘The Endotheliome: A New Concept in Vascular Biology’ (published in Thrombosis Research in 2011). All this illustrates the importance of this seemingly humble tissue, upon whose health our mental and physical wellbeing depends. And if this structure acts consciously, then perhaps we should consider the possibility that all living cells act consciously.

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*Mary Monro Bsc (Hons) Ost, MSc Paed Ost, FSCCO is an Osteopath, based in Bath, United Kingdom.

Free Will: Has Philosophy Been Eclipsed by Neuroscience?

Norton Junction. With acknowledgement to Adrian the Rock

By Keith Tidman

We make decisions before we are consciously aware of making them. These are the findings of the latest neuroscientific research. Has neuroscience therefore eclipsed philosophy? Has it taken the lead? Does philosophy have anything left to say?

In a much-publicised experiment, a neuroscientist placed people into a ‘functional magnetic resonance imaging’ (fMRI) machine. The aim was to observe brain activity as test subjects performed an activity. The neuroscientist instructed the subjects to press a button either with their right hand or their left hand – but to pay close attention to when they took the decision as to which hand to use. The results surprised the worlds of both philosophy and neuroscience. The scanner revealed brain activity—the brain unconsciously deciding to press the button—a remarkable seven seconds before the test subjects consciously opted to press it. That is, the subjects’ brains committed to decisions before the subjects became aware of making them.

Why should this be important? Why does it matter?

We assume that free will is fundamental to our humanity. Assumptions about free will—conscious agency—engage people on pragmatic levels. In fact those assumptions are the keystone for society’s notions of responsibility. Codes of morality and law necessarily rest—rightly or wrongly—on free will’s existence. Institutions, from government bodies to systems of justice to religions, are built on that keystone. In the absence of an alternative model that ensures order in society, such rules-based institutions hold people accountable for their actions. Human conduct is judged, and responses—praise and reward, or condemnation and punishment—are rendered accordingly. Society assumes that a person may be held responsible only if that person is a ‘morally responsible agent’, in conscious, intentional control of behaviour.

The cautious conclusion to the fMRI experiment was that consciousness may play no role in what a person decides. Other neuroscientists concur in this, based on the results of different tests. But are our conclusions too hasty? Are the results ironclad?

In the context of conscious control, what does the fMRI test really tell us about free will? Is free will an illusion, a tricked brain, misled intuition—and even just a convenience for society to function? The question typically appears something like this: “At the moment a person decides, could she willingly and freely have decided otherwise?” And if we do not enjoy unbridled (‘libertarian’) free will, do we at least have contingent free will? If free will is an illusion, is that so for only those choices made hastily and with minimal thought? Or does free will describe all our decisions? Philosophers have grappled with free will for millennia, of course. But the role of neuroscience in this arena is more recent—and arguably indispensable. This dual track of philosophers and neuroscientists makes it necessary to delineate what unique competencies each field brings to free will. But what are they? And do they each have a role?

By and large, both philosophers and neuroscientists today acknowledge the  cause-and-effect nature of brain activity (the physics, chemistry, biology) and decisions—mind-brain dualism long since having been discarded. Yet our considerations do not end here.

Philosophers, for their part, collaborating with psychologists and anthropologists and others, bring a deep understanding of human behavior. This understanding exists in the context of the roles of institutions and culture in society, informing the ways people make decisions, including whether freely or mechanistically. Philosophers also contribute an understanding of the centuries-long history of conceptualising free will and its alternatives, especially how some of the most brilliant minds have described and debated free will and determinism and the concepts’ variants. This process includes placing those historical notions of free will to the litmus test of analytical logic, to assess soundness. All this vitally informs the science—outside the standard domain of scientists—to ensure that the science remains conceptually and historically grounded.

For their part, neuroscientists, collaborating with physicists and biologists, structure hypotheses and bring increasingly sophisticated technologies and rigorous methodologies to understand cognitive brain function. They correlate those functions to the brain as it makes a decision and the person subsequently is aware of the decision. The aim is to explore—tangibly record and measure through technology—what is happening at the unconscious and conscious levels, and to do so involving more complex decision-making. Independent scientists must duplicate test results. For neuroscientists, this unique framing of the free will-versus-determinism puzzle takes into account diverse factors.  These include the neurons and synapses firing in different regions of the brain, perceptions of reality, people’s genetic makeup, the environment influencing genes’ expression (epigenetics), psychological states, and others. How these factors bear on outcomes of science’s take on free will remains to be explored.

Allowing for the distinctly separate competencies of philosophers and neuroscientists, tackling free choice can best be accomplished jointly: defining the problem, examining alternative models, conjuring hypotheses, developing methods, describing initial conditions, teasing out empirical data, interpreting results. Wherein, it seems, lies the best hope of resolving the free-will debate. Philosophy is far from eclipsed.

We Need Animal Cognition, Not Neuroscience

Posted by Matthew Blakeway

A generation ago, it was thought that neuroscience held the promise of solving many philosophical problems. Looking back now over those lost decades, we are able to see that it failed to solve a single one, and arguably created a new one or two.

The purpose of this post is to introduce a single idea, painted with a large brush: As we see our hopes for answers from neuroscience fading, animal cognition may hold the promise of the future. 

 

Neuroscience, it was thought, would tell us many things: what a mind is, whether humans have freewill, or where in the brain we find these things. It would explain consciousness, morality, evil, or why humans tend to believe in prime-moving inter-galactic omnipotent fairies. While there are still philosophers who hold out hope for answers from neuroscience, the failure of progress is striking. An illustration reveals the way in which the arguments typically fail: in his book Freewill, cognitive neuroscientist Sam Harris argued that brain scans revealed a neural blip the moment before a subject was conscious of choosing to act. This, he considered, demonstrated that freewill is a myth, for the reason that the brain acts before we know it. Yet the argument is too easily neutralised. What was the blip? It may just as well have been one part of the brain going, 'OK, Freewill, this is one for your department.'

There are, on the contrary, significant problems that neuroscience has created. For example, its tendency to believe that the mind is nothing but the brain may open it up to a classic problem of logical systems, identified by the mathematical logician Kurt Gödel. Does Gödel's incompleteness theorem imply that the brain is unable to understand itself, so that neuroscience can have no achievable end-goal? Probably! The computer analogy of the brain is an old one, yet it is still useful. We have been inching towards a neuroscientific view that a brain is a biological computing device. Assuming that this is so, the study of the brain may reveal little about how the software works. In moving towards the view that a human mind has no animal spirits or ethereal magic in it, the consequence for neuroscience is that it is ever less in a position to solve philosophical problems – much as we would not have a hope of proving the Church-Turing thesis, or demonstrating why π is an irrational number, by shifting to a study of computer chips.

It may be more helpful for philosophers to turn to animal cognition as their primary input. This field is producing remarkable new finds, and philosophy would do well to absorb their implications. One of its most conspicuous aspects is the study of pro-social behaviour in animals – in contrast with what zoologist Robert Hinde calls 'human aggression in all its deviousness and complexity'. As a case in point, researchers demonstrated that a rat will help another rat in difficulty without needing a reward – if only humans could be relied upon to so act. While the 18th century philosophical view of humankind might be expressed (adopt a tone of pompous bloviation): 'It is the moral sense that separates men from the wild beasts which live in brutal ignorance,' humans do some pretty nasty things. My suggestion is that humans, while they, too, have inherited 'moral emotions', can out-think their own emotions and can manipulate their behaviour tactically. We need to turn the old view of humankind on its head. We don’t need to explain how we are biologically programmed. We need to understand the anomalies.

Such observations promise a rich new vein for philosophy, and it deserves our attentions. By way of illustration, now that we know that rats are compassionate, we may ask why so many bankers and politicians aren’t. Supposing that an economist should persuade bankers and politicians that everybody will become richer if they act in their own self-interest (as has been the case, starting with political philosopher Adam Smith) – then tactically, bankers and politicians may out-think their pro-social inclinations – to the detriment of the poor, and on an alarming scale at that. In this example alone, animal cognition suggests fresh explorations of morality, freewill, and belief, while the answers to the same may explain no less than why it is that our choices polarise all of humanity today.
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Study notes:

Ben-Ami Bartal, I., Decety, J., & Mason, P. “Empathy and pro-social behavior in rats”. Science. 334, 2011. pp 1427-1430.
Hamilton, W. D. “The Genetical Evolution of Social Behaviour”. Journal of Theoretical Biology, 1964, 7 (1): 1–16.