The Evolution of Thought

“Of all animals man has the largest brain in proportion to his size.”
Parts of Animals, Aristotle

 

Do you ever wake up sensing nearness?

Unlike the Hindu and Buddhist cultures the mythic cosmologies of the West lack a sense of nearness of the divine. In the East the common greeting is in Anjali; the hands are brought to the heart with a small bow in recognition of the divine in the person you are greeting. In this worldview every sentient being carries a spark of the cosmic, the ultimate. In the West it has been taught the individual has a soul, not quite the same thing at all.

I find this interesting because in my view the most astonishing features of existence are not the far reaches of space or the mind numbing expanse of the universe as a whole. The most astonishing thing is that all this enormous planetary and stellar matter is so very simple in structure compared to organic chemistries. We find the most complex organization of molecules, if you will, anywhere in the universe, to be right here on planet earth. An interesting contemplation is to sense how all the voluminous yet simple matter in our solar system through its gravitational participation is a necessary support of the rich bounty of earth’s fruitfulness. After all, if any one thing was different, all things would be different. That is what it is to be in a universe of total interdependence, a universe like ours.

If we then ask where we find the pinnacle of organizational complexity among organic matter, the brain is said to have no equal. As ‘possessors’ of said brains we are also familiar with their ability to share their thoughts, like we are doing right now.  In Anjali the greeting ritual lifts social interactions to a magical place, one recognizing something like the uniqueness we find in the grey matter. ‘Hello expression of complexity flowering in the universe, I greet you.’ I think it better captures the dignity of an encounter in which the mystery of my awareness touches the mystery of your awareness.

The contemplative has taken their vehicle to be the mind. In Tibetan Buddhism there is the tradition of the three year retreat. Like the traditional Anjali  this too is interesting. It is as if this culture has a tradition of putting the human mind on the altar in recognition of its actual cosmic value. In three years, three months, and three days it is said the yogi can map the mind, familiarize themselves with its outer reaches and in some ultimately inexpressible way, master non-dual awareness. As children of the space age it is easy to feel the real action in the universe is happening somewhere else. With Anjali and retreat traditions we are being asked to reconsider that, invited to consider that we may be looking through the wrong end of the telescope.

Where did these brains come from? How were they made? How do they work? The first and second questions get a rather satisfying answer from evolutionary studies and we will examine them a bit momentarily. The third question is less amicable to the desire for settled answers, though I will suggest modern neuroscience and cognitive science have advanced far enough to send a few popular yet troublingly misconceived ideas out to pasture.

So what is this mind? To begin the story of where brains come from we need to start with the evolution of the nervous system. Whatever else nervous tissue might be it is certainly a means of sending signals. With signals comes information. What is the selective advantage of additional signal processing?

Learning to adapt to the environment through the accumulation of beneficial genetic mutations is a very slow process by our standards. It takes millions of years for speciation to develop and perhaps hundreds of thousands of years for smaller adaptations to establish themselves. In this environment a premium is placed on any developments that enhance the ability of an organism to respond to their specific environment more skillfully.

Early animals evolved numerous sensory mechanisms for reading their environment. The senses that could pick up environmental clues from a distance carried the highest premium of all. To avoid a mortal threat or find a mate, sight and hearing encompass far more of the environment than taste and smell. This was an environment in which the dynamics of predator and prey drove the selection of the fittest for many, though not all, animal species. It is not hard to understand how even the slightest insight into the state of your world would give you an edge; one percent of an eye, when it is one hundred percent more eye than your neighbors have, is of revolutionary importance.

The earliest animals did not have nervous systems. This limited the amount of information about themselves and their environments they were able to make use of. The development of the nervous system took the ball game to a whole new level. Both the speed by which information travels increases and the information density increases by orders of magnitude. The speed comes because the nervous tissue is able to use electrical impulses instead of chemical diffusion for communications. The density comes due to the many connections possible between neurons due to their dendrite structures.

In Dragons of Eden Carl Sagan presented the following graphic as a way of capturing the information explosion that occurred with the evolution of the nervous system. Genetic information tops out (10 to the 10th) but the human brain information content continues an estimated three more orders of magnitude (10 to the 13th).

BrainGeneticInfo2The evolution of nervous tissue would prove to be wildly successful. “Somewhere in the steaming jungles of the Carboniferous Period there emerged an organism that for the first time in the history of the world had more information in its brains than in its genes.”

Another defining characteristic of the human brain is that it has more mass for its body weight than any other animal on earth. Next in line are the dolphins.  This is captured in the brain to body weight ratio. When this is charted Sagan observes the emergence of mammals and primates “was accompanied by major bursts in brain evolution.”

BodyBrainMassRatioSteven Pinker points out the human brain was considerably re-engineered from the primate brain. “Our brains are about three times too big for a generic monkey or ape of our body size. The inflation is accompanied by prolonging fetal brain growth for a year after birth. If our bodies grew proportionally during that period, we would be ten feet tall and weigh half a ton.”

So where did this path to the brain begin? Last week’s post ended with a look at the segmented nerve cord budding into three distinct areas which become the hindbrain, midbrain and forebrain. Remember, we have this DNA expressing itself through the use of its own regulatory genes. The topological mapping of this evo-devo expression in the nerve cord is segmented at one end into these three distinct regions. We can track these regions throughout the vertebrates’ exploration of the DNA’s design space.

The brain of a fish, which isn’t much, is chiefly midbrain with a tiny forebrain. Reptiles and amphibians are the other way around. Another graphic from the same work shows this by illustrating a perch and a toad. Dr. Sagan also included the development of the nerve cord in a reptile, bird and mammal.

SaganSchematicIt is easy to see how the tinkering with the fundamental components has taken place. Can you hear the three part chord echoing through the long centuries?

What we did not know at the time the Sagan book was written is how the regulatory genes actually work. Today there is a rather clear comprehension of exactly which genes are involved. It is an impressive example of information being conserved across a wide spectrum of phenotypes.  In From DNA to Diversity (first edition) the authors summarize the role of the three regulatory genes across the three regions this way:

DNAToDiversityVertBrainFrom the trail of clues left in the DNA evidence the subdivision of the vertebrate brain into fore, mid and hindbrains came before the mammalian neocortex. The last common ancestor had localized, discrete domains of these regulatory gene expressions.

From observation such as these a model of the brain as a triune structure was developed. In this model of the human brain the later parts are added to those that had evolved earlier. The argument for the model relies on the fact that we find some biological elements conserved through evolutionary changes. It stands to reason that mutations that tinker with some of the deepest features of life are likely to be lethal. In this model of brain evolution the early brain parts are left basically undisturbed while the later parts are added.

The oldest strata is said to be the reptilian brain or the R-Complex, to use Paul MacLean’s term. He also refers to a neural chassis consisting of the midbrain and hindbrain. These contain the neural circuitry for reproduction, respiration, heart rate, blood circulation and other systems necessary for self-preservation. They evolved several hundred million years ago. Surrounding that is the limbic cortex which is said to be the seat of the emotions and is associated with the caregiving of the young we find in the mammals. It likely evolved more than one hundred and fifty million years ago. Finally there is the outermost layer consisting of the neocortex which becomes ever more elaborate in the more advanced mammals. It is believed to have evolved tens of millions of years ago, though a leap in its complexity occurred just a few million years ago with the emergence of humans.

In this model the brain consists of three very different modalities, only one of which is graced with speech. Each has its own mentality, intelligence, sense of space and time and its own memory and motor functions. The distribution of the neurotransmitters dopamine and cholinesterase are also found to be strikingly different in each section. We could say the R-Complex is performing dinosaur functions and the limbic cortex is “thinking the thoughts of pumas and ground sloths.”

Culturally we recognize our lower animal nature as reptile-like when we speak of the ‘cold blooded killer’ or when Machiavelli advises his Prince “knowingly to adopt the beast.” It is not hard to recognize the aggressive, territorial, ritualistic behaviors and rigid social hierarchies of the reptiles within our politics of empires and armies.

Care of the young is mostly found among birds and mammals though there are exceptions among the social insects. The development of the limbic cortex is thought to have brought with it these altruistic behaviors. In this model love was invented by the mammals.

With the arrival of the neocortex comes the ability to plan, to think ahead and to consider options. Instead of a potential meal relying only on instinctual jumping or zigging and zagging to escape their predator threat, an animal equipped with a neocortex can also look for an escape route unique to the exact environment in which the confrontation is occurring.

There is something very familiar to western ways of thinking about our humanity in this triune brain model. It is not hard to see Freud’s id, ego and superego in its threefold classification scheme. More anciently, in Phaedrus Plato likened a human being to a chariot being drawn by a set of black and white horses. Popularizers of the triune brain theory pointed out it mapped well to this Platonic insight when the chariot is likened to the neural chassis, the horses to the R-Complex and limbic systems and the neocortex to the charioteer.

The triune brain seems a fairly good model of both brain physiology and human experience. The model is quite popular, quite well known, almost as if it was a theory made to order, one that confirms our expectations. This should make us wary.

Advances in neuroscience have shown the triune model of the brain to be of limited usefulness, even misleading. Just why and what we have found to be the case instead is what we will look at next week.

Evolutionary Information

Do you wake up sensing vastness?

Unlike the Hindu and Buddhist cultures, the mythic cosmologies of the West lack a sense of vastness. In the East images like Indra’s Net have been used to illustrate existence by likening it to a vast net of diamonds, all reflecting one another just as mirrors in a fun house, where every diamond is a whole universe unto itself. It is a common eastern understanding of existence that it has had no beginning and will have no end so that time exists ceaselessly as universes are endlessly born and die in vast cosmological cycles. Instead of all things being created by a single creator god they recognize a creative ground of all things, gods included. When your eyes blinked open this morning, according to this way of interpreting the experience of being alive and awake, surrounded by mystery, you found yourself again consciously aware in the midst of this vastness of both time and space. The vastness exceeds human thought and imagination in a way not that dissimilar to the vastness we in the West can appropriate by studying astronomy and the ecology of deep time.

I don’t think we properly appreciate the preciousness of what we are putting at risk. A truly heart-felt gratitude for the biosphere and all it offers us requires a sense of just how vast the biological deep time of our planetary evolution actually is. It is important to try and understand viscerally that of the approximately 4 billion years in which life has been evolving, approximately 3 billion of those years were taken up with the evolution of microorganisms, which are still by far the most dominant life form on the planet. It is important to try and understand viscerally that more than 99% of all species that have ever lived are currently extinct, that all the overwhelmingly diverse biological forms we see about us today represent nothing more than the slightest tip of the iceberg.

I see the study of life in the fields of evolution and ecology somewhat like the symbols in the Masonic lodge. All the symbols are there and the terms are accurate but like the neophytes in the lodge we are prone to misunderstand what they mean. We are blind to the real implications of these symbol systems, these sciences, for our lives. Contemplation is our initiatory methodology by which the understandings of the adepts can be acquired. Less poetically: if you really get it, you live it. Climate change is not just a political football and green marketing opportunities. The eco-crises are not just for our entertainment. Something much more powerful is going on here for our species, something involving planet wide forces across deep time and its dream time. Dream time, as I understand it, is like Jung’s collective unconscious or our shared consciousness, or the summation of all that is conscious.  Something like this exists emergent among us since human consciousness is not separate and isolated from the rest of life’s awareness in which it is rooted. In order to tune into that, the small worldview of consumerism needs to be left far, far behind. The heart is noble, yet it remains a choice for each and every one of us whether or not to heed the wakeup call in the age of limits. With evolution and ecology we are in the temple’s Holy of Holies where it would be wise to take off our shoes, for we are treading on our sacred ground.

We have been looking into the ins and outs of evolutionary mechanisms the past few weeks. The recommended contemplations have been around the extent of evolution’s reach, its all-encompassing nature. This has been offered to try and provide us with some felt sense of just how vast the living network of our planetary biosphere really is. Earlier we looked at how easy it is for our minds to form abstractions and generalizations which while helpful in some contexts also blind us to the actual. In nature we find everything is unique and at least a little bit different than its neighbor; every blade of grass, every leaf, every mouse and every elephant. These are the differences that are all important from the evolutionary perspective. To really appreciate what is involved requires, it seems to me, a concomitant appreciation of the vastness of the forms and forces involved. Otherwise our understanding is threatened by an overly simple generalization of the subject which leaves the impression of the biosphere as an unthinking machine.

The metaphor of the biosphere as a machine is a popular one in our culture; it all has to exist for some purpose like a machine and was designed for achieving that purpose like a machine and uses energy to engage flows of inputs to produce transformed outputs like a machine. Enamored as we are with gadgets and machines, when we encounter something like the DNA molecule our default interpretive context for it naturally involves machine-like characteristics. We see abstractions and generalizations where in fact the products are all concrete and specific; there is no turtle, there is only this turtle here, and that turtle over there, indeed it is specific, individual turtles all the way down. Because we see abstractions instead of the particulars which are the abstractions referents these machine like characteristics seem dominant among the evolutionary and ecological processes.

That organisms are the antithesis of machines is of course a bit of a problem for these models. Machines do not learn nor reproduce yet these are the very characteristics defining evolution. Machines do not grow and move through lifecycle stages yet this is the very characteristics defining evolutionary development, evo-devo. With these antimonies in mind what, we might ask, is the reason a machine-like model has been dominant in the biological fields? The answer is doubtless many faceted and complex. The cynic will point out how a model of nature as machine holds out the promise of mankind one day completely understanding and controlling it. Knowledge is power in this model and a machine is theoretically transparent to the understanding. There is some truth in that analysis and it is worth developing. However, there is another similarity I propose is more relevant, namely computing. To appreciate it will require a bit of history.

Darwin’s 1859 publication came on the heels of what historians refer to as the industrial revolution. The discovery of evolution by natural selection occurred at a time and place where applying scientific insight through the technological design of machinery had thoroughly transformed individual lives, societies and both the urban and rural environments in which they found themselves. When Origin of the Species was published there was no clear understanding of how descent with modification happened in living things, only that undeniably it did. By the time the actual mechanism of genetic inheritance was discovered and the structure of the DNA molecule was mapped in the 1950s, the cutting edge of technological development was learning how to produce computers – information processing machines. Here is where I see a metaphorical similarity between machine and DNA processes. The amino acid pairs might be similar to Lego-like building blocks familiar to numerous technologies but it is with the information processing machines that we encounter an almost uncanny alignment of biology and engineering. From the bacterial chemical exchanges to the pulse patterns of the nerve cord we find systems that embody information and assist its exchange have been favored by evolution throughout the animal kingdom.

The evolution of eyes, wings, lungs, hands, skin, skeletal joints, and all the other features of animal physiology are fascinating and full of lessons but I want to focus our attention around the evolution of the nervous system, the information carrying stratum par excellence.PurkinjeCellThe basis of the nervous system is the neuron which is typically formed with a set of branches at one end called its dendrites, a cell body and a single axon. The dendrite tree extends a few hundred micrometers as it branches, whereas the axon of a single neuron cell can extend up to a meter in the human body. There are families of neurons specialized as sensory neurons, motor neurons and interneurons or those which connect neurons together as we find particularly in the brain and spinal cord.

The neuron is a cell specialized to transmit an action potential. The evolution of the action potential occurred in the single celled eukaryotes as they found a quick electrical pulse along their membrane a useful way to activate biochemical pathways within the cell. The details of the voltage gated ion channels which produce the action potential need not concern us here, though it is helpful to know there are two main types. In one a sodium channel is used and the action potential lasts under a millisecond and in the second a calcium channel is used and its action potentials can last 100 milliseconds or even longer. These nerve impulses or spikes travel the length of the neuron’s single axon. The interneurons typically respond to the spike by releasing neurotransmitters which in turn excite neighboring neuron’s dendrites. In this way a signal is sent across the synaptic gap and communication occurs.

The Jellyfish and similar animals use a set of neuron cells structured as a web, a nerve net. With this relatively primitive structure they are able to absorb sensory inputs, process those signals and use them to activate muscles and other physiological processes.  Already in the nerve net the fundamental capability of the nervous system is beautifully illustrated. They provide a window on the world through their ability to sense visual, chemical, tactile, taste and odor signals. There is something very magical about how the senses bridge the inner and outer worlds. These nerve nets also provide the orchestration required for numerous life support systems, from muscle contractions to the production of insulin.

Tinkering with the nerve net over deep time resulted in the development of the nerve cord, what in humans is expressed as the spinal column. With the introduction of a centralizing feature body forms take on the bilateral symmetry that is found extensively throughout the animal kingdom. The phenotype in which the left and right sides mirror each other is constructed around a tube running mouth to anus and a nerve cord with a ganglion or enlargement at each of the body segments.

Bilateral animals can be divided into two camps depending on how this nerve cord is positioned during the early stages of their embryonic development. Early evo-devo expressing the DNA information will position the nerve cord either on the front or backside of the trunk. Insects for example have the nerve cord running along the ventral midline whereas vertebrates have it running along the dorsal midline. Basically the segmented body arrangement is flipped over so where one has the cord running along the back, the other has it running along the belly. There are numerous other features of these two groups’ phenotypes that are also inverted.

HoxGeneRemember the body segments from the fruit fly we saw in this picture when we were discussing evo-devo? The segmented body plan along the trunk of an animal is laid out in the nerve cord through a series of narrow bands. The body innervation pattern follows those segmentations. It is not at all dissimilar to the classic image of the yogic chakra system with the chakras corresponding to the major ganglions.

nadisThe top three segments of the segmented body plan laid out in the nerve cord are what become in modern humans the forebrain, midbrain and hindbrain. We will begin looking into that a bit next week.