The Evolution of Mind and Mathematics: Dehaene Versus Plantinga and Nagel

Today the leading philosopher defending religious belief is Alvin Plantinga.  He is a theistic evolutionist, who argues that theism is not just compatible with, but absolutely necessary for evolutionary science, and indeed for all of science.  As I have indicated in a previous post, I agree with him about the compatibility of theism and evolution, because evolutionary science leaves open the question of whether nature might ultimately depend upon God as First Cause.  But I disagree with his claim that theistic belief is absolutely necessary for evolutionary science.

In his evolutionary argument against naturalism, Plantinga has argued that atheistic naturalism is self-defeating, because if we believe that our minds evolved by natural selection unguided by God's divine mind, then we have no reason to trust our mind's capacity for grasping the truth, and thus we have no reason to trust our belief in atheistic naturalism.  In some previous posts (here and here), I have suggested that Plantinga's argument fails because it assumes a radical Cartesian skepticism that is implausible, by assuming that human beings could be naturally evolved for being in a state of complete and perpetual delusion.

Plantinga has now elaborated his reasoning in a new book--Where the Conflict Really Lies: Science, Religion, and Naturalism (Oxford University Press, 2011).  His general claim in this book is that "there is superficial conflict but deep concord between science and theistic religion, but superficial concord and deep conflict between science and naturalism" (ix).

Thomas Nagel has written a favorable review of this book in The New York Review of Books (September 27, 2012).  (In a previous post, I have written about Nagel's review of David Brooks' The Social Animal.)  This might seem surprising since Nagel is an atheist.  But it's understandable if one has read Nagel's new book--Mind & Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False (Oxford University Press, 2012).  Nagel criticizes what he takes to be the "reductive materialism" of Darwinian naturalism for failing to explain the reality of mind as manifested in human consciousness, cognition, and morality.

I agree with Nagel that a strongly reductionistic science--reducing all phenomena to physics and chemistry--cannot explain mental experience.  But what are the alternatives?  To explain the history of the appearance of mind in the universe, there are, he suggests, at least three alternatives: the historical account must be either causal (law-governed efficient causes), teleological, or intentional.  The causal account will be reductive, if one believes that the most elementary particles of nature are somehow mental, or emergent, if one believes that at some point in the evolution of natural complexity mental capacity arose as an irreducibly complex phenomenon.  In some previous posts, I have argued for the evolutionary emergence of the mind in the brain.  Nagel rejects this without much explanation because it "seems unsatisfactory" or "seems like magic" (55-56).  Although I agree that there might be some natural mystery in the emergence of mind in body, I don't see why we cannot accept this as a natural phenomenon that can be plausibly explained through an evolutionary science of the brain.

What Nagel calls the "intentional" account is the theistic explanation of Plantinga and others (including the proponents of "intelligent design"):  the universe was created by a Divine Mind that created human beings in His image as having minds like His.  According to Plantinga, God has created human beings with a sensus divinitatis--the gift of faith--so that most human beings believe in God's existence without any need for rational proof.  Atheists like Nagel suffer from a form of spiritual blindness.  In his article for the New York Review, Nagel explains: "My instinctively atheistic perspective implies that if I ever found myself flooded with the conviction that what the Nicene Creed says is true, the most likely explanation would be that I was losing my mind, not that I was being granted the gift of faith."

This leaves Nagel with the "teleological" explanation for the place of mind in the universe.  He favors this explanation although he admits that he does not yet understand how to fully develop it.  His idea is that from the very beginning of the universe there was an end or purpose inherent in things that would inevitably lead to the appearance of mind.  It's as though there was a cosmic mind from the beginning guiding the entire history of the cosmos towards the human mind.  He calls this natural teleology, and he insists that there is nothing supernatural or theistic about it.  But what he says about it sounds religious to me.  He writes: "Each of our lives is a part of the lengthy process of the universe gradually waking up and becoming aware of itself" (85).  What does this mean?  The Cosmic Mind was asleep, but then it woke up in our minds? 

If Nagel rejects my belief in the emergent evolution of the mind in the brain because it "seems like magic," then I will reject his belief in the sleeping Cosmic Mind that wakes up because it seems like mysticism.

Consider the case of mathematics.  How do we explain what physicist Eugene Wigner called "the unreasonable effectiveness of mathematics in the natural sciences"?  How do we explain the amazingly precise fit between the mathematical abstractions developed in the human mind and the natural regularities of the external world, which makes natural science possible? 

Plantinga explains this as an example of the "deep concord" between theism and science (284-91).  He quotes Paul Dirac: "God is a mathematician of a very high order, and He used advanced mathematics in constructing the universe."  We cannot trust our mathematical knowledge of the world, Plantinga argues, unless we believe that God is a mathematician who created the world mathematically and created our minds to grasp its mathematical order.

Nagel's alternative explanation would manifest his Platonic idealism: the whole universe is somehow ruled by an impersonal Cosmic Mind that is mathematical, which "wakes up" in the mind of the human mathematician.

The Darwinian view that I embrace is open to Plantinga's theistic explanation as conceivable: it is possible that the Divine Mathematician created the world so that the human mind would arise from a natural evolutionary process with a capacity for mentally grasping the mathematical order in the world.  But even if one is skeptical of such beliefs, because one lacks the gift of faith (the sensus divinitatis), one can still explain mathematics as a purely natural product of the emergent evolution of the mind in the brain.

A good elaboration of this position is Stanislas Dehaene's The Number Sense: How the Mind Creates Mathematics (Oxford University Press, 1997).  Dehaene is a mathematician who became interested in the evolution of mathematics as a product of both genetic evolution and cultural evolution.  In particular, he set out to explain the evolution of the "number sense."  Summarizing his reasoning, he writes:

That the human baby is born with innate mechanisms for individuating objects and for extracting the numerosity of small sets.

That this "number sense" is also present in animals, and hence that it is independent of language and has a long evolutionary history.

 That in children, numerical estimation, comparison, counting, simple addition and subtraction all emerge spontaneously without much explicit instruction.

That the inferior parietal region of both cerebral hemispheres hosts neuronal circuits dedicated to the mental manipulation of numerical quantities.

Intuition about numbers is thus anchored deep in our brain.  Number appears as one of the fundamental dimensions according to which our nervous system parses the external world.  Just as we cannot avoid seeing objects in color (an attribute entirely made up by circuits in our occipital cortex, including area V4) and at definite locations in space (a representation reconstructed by occipitoparietal neuronal pathways), in the same way numerical quantities are imposed on us effortlessly through the specialized circuits of our inferior parietal lobe.  The structure of our brain defines the categories according to which we apprehend the world through mathematics. (244-45)
 

According to Wigner, "the miracle of the appropriateness of the language of mathematics to the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve."  And according to Johannes Kepler, "the principal object of all research on the external world should be to uncover its order and rational harmony which were set by God and which he revealed to us in the language of mathematics." 

By contrast, Dehaene denies that there is any need to see a miracle in the correspondence between mathematics and nature if one explains this as the outcome of natural evolution.  Even nonhuman animals show a number sense that has evolved to help them survive and reproduce because it helps them to track the regularities in the natural world.  The same is true for human beings, except that human beings have a unique capacity for symbolic abstraction that allows them to develop mathematical symbolism far beyond the capacity of other animals.  The cultural evolution of mathematical symbolism in human history is an evolutionary process of trial and error in which some mathematical systems are more effective than others, and some of those mathematical ideas turn out to be useful for understanding the natural world.

To which Plantinga responds:

     Of course it is always possible to maintain that these mathematical powers are a sort of spandrel, of no adaptive use in themselves, but an inevitable accompaniment of other powers that do promote reproductive fitness.  The ability to see that 7 gazelles will provide more meat than 2 gazelles is of indisputable adaptive utility; one could argue that these more advanced cognitive powers are inevitably connected with that elementary ability, in such a way that you can't have the one without having the other.

     Well, perhaps; but it sounds pretty flimsy, and the easy and universal availability of such explanations makes them wholly implausible.  (287)

On the contrary, such explanations seem very plausible to me, especially when one realizes that the correspondence between mathematics and nature is not exact but only an approximation.  The discovery by Pythagoras that irrational quantities were required to express the incommensurability of the diagonal of a square was deeply disturbing to the ancient Greeks.  But this is not surprising if one sees that mathematics has evolved in the mind as only an approximation of the order in nature.  Similarly, while Kepler thought that the elliptic trajectory of planets in the solar system manifested the mathematical genius of God, the fact that these trajectories are only rough approximations to ellipses might make us doubt the exactness of God's mathematics.

Was Man Created in God's Image? Or in the Image of Primates, With 16 Billion Neurons in His Cerebral Cortex?

 

                                  The Hidden Neuroscience in Michelangelo's "Creation of Adam"

THE CREATION OF ADAM'S PREFRONTAL CORTEX

Michelangelo's "Creation of Adam" is his visual depiction of the teaching in Genesis 1:27--"So God created man in his own image, in the image of God created he him; male and female created he them" (KJV).  Remarkably, Adam's body is already fully formed, but God is going to transmit to him something essential to his humanity through God's extended finger.  Presumably, God is endowing Adam with a human soul.  But how exactly is that to happen?  

We should notice that Michelangelo chose not to depict another image of Adam's creation from Genesis: "And the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul" (2:7).  Michelangelo decided not to show God breathing into Adam's nostrils the breath of life as the source of ensoulment.

So what is it about the image of God flying through the air and stretching out his arm towards Adam lying on the ground that conveys the emergence of a human soul in Adam?  Some neuroscientists have pointed out that one can see a hidden drawing of the human brain in the image of God.  And God's right arm is extended through the prefrontal cortex, which is the part of the cerebral cortex responsible for decision-making, planning, creativity, working memory, and language.  Previously, I have written about how the liberty or freedom to choose between alternatives is a function of the cerebral cortex, under prefrontal control, in its reciprocal interaction with the environment. 

Is This a Hidden Drawing of the Human Brain?

We know that Michelangelo studied human anatomy carefully, and that he dissected human bodies and brains.  We know this from his anatomical drawings.  (Leonardo da Vinci--a contemporary of Michelangelo's--was also a talented anatomist of the brain.)  But of the thousands of Michelangelo's drawings, he destroyed most of them, and only about 600 have survived.  Some of these show drawings of the human skull and brain, but none of them show the exact outline of the cerebral cortex that some neuroscientists have seen hidden in Michelangelo's pictures.  There is certainly no evidence that Michelangelo understood the cognitive functions of the cerebral cortex and the prefrontal cortex.  Seeing a hidden neuroscientific message in Michelangelo's picture seems fanciful.

Nevertheless, we could argue for a modern neuroscientific revision of Michelangelo's picture, in which the image of God could be replaced by the image of the human cerebral cortex.  This would not have to be seen as an atheistic revision of the picture.  Because if the theistic evolutionists (like Francis Collins, Deborah Haarsma, and the last three Catholic popes) are correct, then God works through the natural laws of evolution to execute His creative design.  Some of the theistic evolutionists (like Pope Francis) say that while God works mostly through natural evolution rather than miracles, the creation of the human soul did require an "ontological leap"--a supernatural miracle--that transcended natural evolution.  But as I have argued, there are good reasons to believe that the natural evolution of the primate brain can explain the emergence of the soul in the human brain, so that no miracle was required.  And yet we still have to wonder what properties of the evolved human brain explain the amazing intellectual and emotional capacities of the human mind.

COUNTING NEURONS

Over the past fifteen years, the research of Suzana Herculano-Houzel, a Brazilian neuroscientist now at Vanderbilt University, has shown how this natural evolution of the human brain can be understood as based on the remarkable number of neurons in the human cerebral cortex, as it has emerged from the evolution of the primate brain, and thus we can see that we were created in the image of other primates, just as Charles Darwin suggested in 1871 in The Descent of Man (Gabi et al. 2016; Herculano-Houzel 2016, 2021; Herculano-Houzel and Lent 2005).  I am persuaded by most of what Herculano-Houzel says, although I will identify two points of disagreement with her.

                                                Suzana Herculano-Houzel Counts Neurons

How many neurons are in the human brain?  For many years, the answer from many scientists was 100 billion.  But, surprisingly, when Herculano-Houzel began some years ago looking for the original scientific research that provided evidence for this number, she found nothing.  She discovered that neuroscientists had repeated this number over and over again without realizing that there was no scientific verification for it.  

Moreover, she discovered that scientists had no reliable method for counting brain cells.  The most common method for attempting to do this was stereology: virtual three-dimensional probes are placed throughout thin slices of brain tissue from some part of the brain, then the number of cells within the probes are counted, and finally this is extrapolated to the total number of cells in the entire tissue volume.  The problem is that this works only for tissues with a relatively homogeneous distribution of cells.  In fact, the highly variable density of neurons across different structures of the brain, and even within a single structure, makes stereology impractical for counting the cells in whole brains.

Herculano-Houzel developed a new technique for counting neurons that starts with creating brain soup.  She dissects the brain into its anatomically distinct parts--such as the cerebral cortex, the cerebellum, and the olfactory bulbs.  She then slices and dices each part into smaller portions.  Next, she puts each small part in a tube and uses a detergent that dissolves the cell membranes but leaves the cell nuclei intact.  By sliding a piston up and down in the tube, she homogenizes this brain tissue into a soup in which the nuclei are evenly distributed.  She stains all the cell nuclei blue so that she can count them under a fluorescent microscope.  She then adds an antibody labeled red that binds specifically to a protein expressed in all neuronal cell nuclei, which distinguishes them from other cell nuclei such as glial cells.  Going back to the microscope, she can then determine what percentage of all nuclei (stained blue) belong to neurons (now stained red).  Finally, she can estimate the number of neurons for each structure of the brain.  She has done this in studying the brains of many mammalian animals.

Now she can tell us that the total number of neurons in the whole human brain is not 100 billion but 86 billion.  Of that total, 16 billion are in the cerebral cortex, which includes 1.3 billion neurons in the prefrontal cortex.  The cerebral cortex is the outer covering of the surfaces of the cerebral hemispheres.  The prefrontal cortex covers the front part of the frontal lobe of the cerebral cortex located behind the forehead.

FOUR ADVANTAGES

Comparing the numbers of neurons for the human brain with the numbers for other primate brains and other mammalian brains allows Herculano-Houzel to explain the conundrum of how the human brain can be at once so similar to and yet so different from other animal brains.  She makes four arguments about how the human brain gives human beings four kinds of advantages in their mental abilities: the primate advantage, the human advantage, the advantage of cooking, and the advantage of cultural learning.

Her claim that differences in cognitive capabilities across species can be explained by differences in the absolute numbers of neurons depends on a fundamental assumption.  If neurons are the basic units of brain networks for processing information, and if the networks are structured in similar patterns, then the greater the number of neurons in a network, the greater the capacity of the network for processing information.

The primate advantage.   Not surprisingly, larger brains tend to contain more neurons than smaller brains.  But different groups of animals show different scaling rules in proportioning brain size to number of neurons.  For example, a rodent cortex will have fewer neurons than a primate cortex of similar mass.   Primates always concentrate larger numbers of neurons in the brain than rodents of a similar, or even larger, brain size.

So here a capybara brain of 76 grams has 1.6 billion neurons, while a capuchin monkey brain of 52 grams has 3.7 billion neurons.  Comparison of primates with other mammals shows the same primate advantage:  in primate brains, the neurons are packed more tightly in a similar volume.  As primate brains, human brains have the same primate advantage over other mammals.  Thus, while the number of neurons in the human brain is remarkable, it is not extraordinary, because it falls on the primate scaling line: it's what one would expect for a primate with a body the size of the human body.  As Herculano-Houzel says: "The human brain is just a scaled-up primate brain: remarkable but not special."

One common objection to this is that the bodies of gorillas and orangutans can be as large as human bodies, but the brains of gorillas and orangutans are only about one-third the size of the human brain.  Gorillas and orangutans can weigh about 165 pounds, but their brains have only about 30 billion neurons, in contrast to the 86 billion neurons in the human brain.  Doesn't this show that the human brain is three times larger than what one would expect for a primate with the same size body? 

Herculano-Houzel's answer is that if one excludes the great apes (gorillas and orangutans), the scaling of the human brain in proportion to body size follows the same scaling rule as all other primates.  So the outliers here are not human beings but the great apes: it's not that human brains are too large for their bodies, but that gorillas and orangutans have brains that are too small for their bodies.

She explains this as showing that as primate evolution reaches the outer limits of the primate energy budget--the extra effort to find food--there is a tradeoff between brains and brawn.  More energy for a big body means less energy for a big brain.  The evolutionary history of the great apes shows a tradeoff  favoring big bodies and small brains.  By contrast, the evolutionary history of the human species shows a tradeoff favoring a typically primate slim body but a big brain.

The human advantage.  Herculano-Houzel's counting of neurons has allowed her to see that we human beings have one great advantage over all other animals: "we are the species that owns the largest number of neurons in the cerebral cortex--the part of the brain responsible for finding patterns, reasoning logically, expecting the worst and preparing for it, developing technology and passing it on through culture" (2016, x).  Notice that she is not saying that we have the largest number of neurons in the whole brain.  The African elephant brain has 257 billion neurons, three times our count of 86 billion.  But an amazing 98 percent of the elephant's neurons are in the cerebellum.  Although the elephant's cerebral cortex weighs over 6 pounds, it has only 5.6 billion neurons, far fewer than the 16 billion neurons in the human cerebral cortex weighing 2.6 pounds.  The sperm whale has the largest animal brain--weighing about 18 pounds--but Herculano-Houzel predicts that the number of neurons in the sperm whale's cerebral cortex is probably far fewer than 16 billion.

What Herculano-Houzel says about this human advantage confirms what I have argued about how the human mind or soul can arise from a natural process of emergent evolution in which differences in degree become differences in kind after passing over a critical threshold in the size and complexity of the primate brain.  As a consequence of her research, I can now identify that critical threshold as the remarkably large number of neurons in the human cerebral cortex and particularly in the prefrontal cortex.  Unfortunately, she herself does not see how her research supports the idea of emergent evolution.  That's my first disagreement with her.

In her book chapter on Darwin's Descent of Man--particularly, Darwin's chapter on "Comparison of the Mental Powers of Man and the Lower Animals"--she supports Darwin's claim that human mental powers differ from the mental powers of other animals only in degree and not in kind, and that if this difference were a difference in kind, that would deny his theory of human evolution from lower animals (Herculano-Houzel 2021, 48-49, 51, 61).

Herculano-Houzel does not see that Darwin in The Descent of Man is forced to contradict himself by both affirming and denying that there are differences in kind between human beings and other animals in their mental capacities.  Despite Darwin's explicit statement that humans differ only in degree, not in kind, from other animals, he implicitly recognized differences in kind.  That is to say, Darwin recognized that human beings have some mental traits that other animals do not have at all.

Darwin noted that self-consciousness is uniquely human: "It may be freely admitted that no animal is self-conscious, if by this term it is implied, that he reflects on such points, as whence he comes or whither he will go, or what is life and death, and so forth" (Descent, Penguin edition, 105).  Morality is also uniquely human: "A moral being is one who is capable of comparing his past and future actions or motives, and of approving or disapproving of them.  We have no reason to suppose that any of the lower animals have this capacity. . . . man . . . alone can with certainty be ranked as a moral being" (135).  And language is uniquely human: "The habitual use of articulate language is . . . peculiar to man" (107).

Darwin could implicitly affirm such emergent differences in kind without affirming any radical differences in kind.  Emergent differences in kind can be explained by natural science as differences in kind that naturally evolve from differences in degree that pass over a critical threshold of complexity.  So, for example, we can see the uniquely human capacities for self-consciousness, morality, and language as emerging from the evolutionary increase in the neurons of the primate brain, so that at some critical point in the evolution of our ancestors, the size and complexity of the brain (perhaps particularly in the frontal cortex) reached a point where distinctively human cognitive capacities emerged at higher levels of brain evolution that are not found in other primates.  With such emergent differences in kind, there is an underlying unbroken continuity between human beings and their hominid ancestors, so there is no need to posit some supernatural intervention in nature that would create a radical difference in kind in which there is a gap with no underlying continuity.  

Like Darwin, Herculano-Houzel fails to see how evolutionary science can recognize emergent differences in kind that arise from natural evolution while denying radical differences in kind that would require supernatural miracles.

The advantage of cooking.  If human beings are created in the image of primates, and yet they are unique among the primates because of those 16 billion neurons in the human cerebral cortex, why are human beings the only primate species to evolve such an increase in those neurons?  Herculano-Houzel's answer is that the evolutionary expansion of the human brain was made possible by the human invention of cooking.  Here she adopts the cooking hypothesis of Richard Wrangham in his book Catching Fire: How Cooking Made Us Human (2009).

The energy cost of the human brain is huge.  The brain is only 2 percent of the total body mass, but it consumes on average about 25% of the daily total energy budget for the human body.  On average 3.3 billion molecules of glucose are consumed per human neuron per minute.  6 kilocalories are consumed per billion neurons per day.  And so the more neurons in a brain, the more energy that a brain costs.

The caloric intake from the typical raw food diet of primates is not enough to supply the energy needs of the human brain.  The human controlled use of fire and the invention of cooking about 1.5 million years ago expanded the daily supply of energy to support the evolutionary expansion of the human brain, which can be seen in the fossil record of the huge expansion of the brain from Homo erectus to Homo sapiens.

The slicing and dicing of food and cooking with heat start the process of digesting food before it enters the mouth.  Cooking with heat breaks down the collagen fibers of meat and softens the hard walls of plant cells.  Cooked foods yield 100 percent of their caloric content to the digestive system.  Without cooking, our ancient human ancestors could never have fed their hungry human brains.

In a previous post, I have suggested that this cooking hypothesis for human evolution confirms what Lucretius said about the importance of fire and cooking for the evolutionary emergence of a fully human species.

The advantage of cultural learning.  The controlled use of fire and cooking are technologies that are invented and passed down across the generations by cultural learning.  As Herculano-Houzel observes, this shows us that "plenty of neurons aren't enough," because while having lots of neurons endows a brain with the capacities for complex cognition, turning those capacities into abilities requires cultural learning across an individual lifetime and across many human generations.

As I have indicated in some previous posts, cultural learning is not uniquely human because some other animals have cultural traditions of behavior.  But human beings are unique in their capacity for symbolic culture.

The behavioral inheritance system is the transmission of information among animals through social learning. For example, among some animals (including human beings) mothers transmit food preferences to their offspring, because information about what mother is eating is transmitted either in the womb or through suckling, so that the offspring inherits a preference for that food. More complex forms of social learning come through animal culture. For example, some chimpanzees can discover how to open nuts with a stone, and then pass on this practice within their group so that it becomes a social tradition. Different communities of chimps in Africa have different cultures based on distinctive profiles of traditional practices transmitted by social learning. As opposed to genetic evolution, cultural evolution is not blind but targeted to functional change.

The symbolic inheritance system is uniquely human because it shows the qualitative leap that defines our humanity as based on our capacity for symbolic thought and communication. Other animals can communicate through signs. But only human beings can communicate through symbols. The evolution of human language was probably crucial for the evolution of symbolism. Symbolic systems allow us to think about abstractions that have little to do with concrete, immediate experiences. Symbolic systems allow human beings to construct a shared imagined reality. These symbolic constructions are often fictional and future-oriented. Art, religion, science, and philosophy are all manifestations of human symbolic evolution. 

Herculano-Houzel gives a good account of human cultural evolution as driven by six technological revolutions (2016, 206-213).  But she doesn't explain why the pace of that technological progress has become so rapid over the past 300 years.  I have argued that the best explanation for this accelerated human progress is the symbolic niche construction of Lockean liberalism, which has sustained the freedom for innovation that has made it possible for the Earth today to support a population of over 8 billion people who are living longer and healthier lives on average than has ever been possible.  That is a stunning enhancement of Darwinian survival and reproductive fitness through cultural evolution.

THE SYMBOLIC EVOLUTION OF RELIGIOUS BELIEF IN "METAPHYSICAL ORIGINS"

The evolved cognitive capacity of the human brain for symbolic cultural learning includes a propensity to religious belief, which can include the belief that human beings were created in the image of God, and that this endowed human existence with a supernatural purpose.  Herculano-Houzel fails to take that religious belief seriously as a part of human cultural evolution, and that's my second point of disagreement with her.  She does say that the human brain gives human beings "the ability to ponder our own material and metaphysical origins" (2016, 215).  But she says nothing more about how the religious belief in "metaphysical origins" might be rooted in the evolutionary psychology of the human brain.  In The Descent of Man, in his chapter on the "mental powers of man and the lower animals," Darwin comments on a long list of mental powers, concluding with "belief in God, spiritual agencies, superstitions."  In her commentary on this chapter, Herculano-Houzel is silent about this.

If she had examined that last part of Darwin's chapter on the evolution of the mental powers as leading to religious belief, she would have seen that Darwin anticipates the modern evolutionary psychology of religion as an expression of the human brain's evolved theory of mind or the "hyperactive agency detection device."  Darwin conveys this idea when he says that the earliest manifestation of religious belief is "when anything which manifests power or movement is thought to be endowed with some form of life, and with mental faculties analogous to our own" (117).  Through symbolic cultural evolution this "belief in spiritual agencies" or animism could eventually be expressed in the belief in the existence of an Omnipotent God who is the "Creator and Ruler of the universe" (116, 118).  This is the God depicted in Michelangelo's "Creation of Adam"--the God who created human beings in His image.

The evolutionary science of the brain can explain how this ability for believing in the existence of the Creator God evolved through the genetic evolution of the human cerebral cortex and prefrontal cortex and the symbolic cultural evolution of religious belief in monotheism.  But while some Darwinian psychologists (such as Justin Barrett) see this as showing that Darwinian science is compatible with the truth of believing in God, others (such as Jesse Bering) see this as exposing belief in God as a fictional construction of the evolved human mind. For those like Barrett, religious belief is an adaptive truth. For those like Bering, religious belief is an adaptive illusion.

Thus, we see that Darwinian science cannot resolve the Reason/Revelation debate.  But Darwinian liberalism can support the freedom of thought that promotes that debate.

Part of that Reason/Revelation debate is whether human beings have a natural need to see the purpose for their existence that can only come from believing in the revelation of a divine purpose for human life, or whether natural reason alone can give human life some purpose or meaning.  Some theistic scientists (like Deborah Haarsma) say that in answering our questions about the Universe, science can tell us when and how, but only religion can tell us who and why.

Friedrich Nietzsche thought that the cultural history of the "teachers of the purpose of existence" over thousands of years had changed human nature so that human beings had a culturally acquired need to see some cosmic purpose to their lives.  "Gradually, man has become a fantasizing [phantastischen] animal that has to fulfill one more condition of existence than any other animal: man has to believe, to know, from time to time why he exists; his race cannot flourish without a periodic trust in life--without faith in reason in life" (The Gay Science, sec. 1).  Consequently, Nietzsche observed, "I fear that the animals consider man as a being like themselves that has lost in a most dangerous way its sound animal common sense; they consider him the insane animal, the laughing animal, the weeping animal, the miserable animal" (sec. 224). 

Is this what happens when you have a brain with 16 billion neurons in its cerebral cortex fed by some delicious, cooked meals?

REFERENCES

Darwin, Charles. 2004. The Descent of Man. 2nd edition.  New York: Penguin Books

Gabi, Mariana, et al. 2016. "No Relative Expansion of the Number of Prefrontal Neurons in Primate and Human Evolution." Proceedings of the National Academy of Sciences 113 (no. 34): 9617-9622.

Herculano-Houzel, Suzana. 2016. The Human Advantage: A New Understanding of How Our Brain Became Remarkable.  Cambridge, MA: MIT Press.

Herculano-Houzel, Suzana. 2021. "Remarkable But Not Extraordinary: The Evolution of the Human Brain." In Jeremy M. Desilva, ed., A Most Interesting Problem: What Darwin's 'Descent of Man' Got Right and Wrong About Human Evolution, 46-62.  Princeton: Princeton University Press.

Herculano-Houzel, Suzana, and Richard Lent. 2005. "Isotropic Fractionator: A Simple, Rapid Method for the Quantification of Total Cell and Neuron Numbers in the Brain." Journal of Neuroscience 25: 2518-2521.

Wrangham, Richard. 2009. Catching Fire: How Cooking Made Us Human. New York: Basic Books.

Von Economo Neurons: The Neural Basis for Self-Awareness, Social Awareness, and the Moral Sense?

In the summer of 1996, I participated in a Summer Institute on the Biology of Human Nature at Dartmouth College, directed by Roger Masters and Robert Perlman.  At the time, I was finishing my book manuscript Darwinian Natural Right: The Biological Ethics of Human Nature; and this Summer Institute helped me think through many of the questions for the book, including the fundamental question of the biological basis for the human mind and morality.

We spent one afternoon at a human dissection lab at Dartmouth Medical School, where a professor of neurology guided us in our dissection of two human brains.  We talked about how the human brain compares with the brains of other animals.  And we asked what might make the human brain unique.  As we sliced up these brains, I remember asking myself: Where's the soul?  How does the soul or mind arise in the evolution of the brain?

At one point, the neurology professor suggested that part of the answer as to the uniqueness of the human brain might be special neurons--particularly, "spindle neurons" that seem to facilitate fast communication across distant neural networks in the large human brain, neurons that are found only in certain areas of the human brain and possibly in some other primate brains.  Looking back on this, I assume that the professor had read a recently published article on spindle neurons in the human anterior cingulate cortex (Nimchinsky et al. 1995).

I was intrigued by this, and I wanted to learn more.  But as far as I could tell, there wasn't much research on these spindle neurons.  Only recently, have I discovered that over the past 15 years there has been intense study of these neurons.  Although the conclusions remain very speculative, there is evidence that these neurons provide some of the neural basis for human self-awareness, social awareness, and the moral sense.

As I have often argued on this blog--most recently in response to Roger Scruton's claim that biological science cannot study the human mind--this sort of research shows how evolutionary biologists can explain the evolutionary emergence of the human mind in the primate brain and body, although the inward experience of subjective self-awareness will always remain somewhat mysterious.

A Cartoon of Von Economo (Spindle) Neurons with Only a Single Dendrite Compared with Pyramidal Neurons with Many Dendrites

The mystery is that while each of us has direct access to our own subjective consciousness, we cannot directly observe the conscious experience of anyone else.  So when neuroscientists put someone in a functional MRI brain scanning machine, the scientists can see what parts of the brain light up in the brain images as indicating neural activity, but they cannot see what the person is thinking or feeling, and so they must ask that person to report what he or she was thinking or feeling. The scientists can then infer that the observed patterns of neural activity are somehow correlated with the reported thoughts and feelings.

Scientists have observed that the anterior insular cortex (AIC) and the anterior cingulate cortex (ACC) on both sides of the brain are jointly active in most functional imaging studies, and that the AIC supports emotional feelings, self-awareness, and social awareness.  Moreover, they have observed that these two parts of the brain have a high concentration of spindle neurons that are not found anywhere else in the brain, except for small numbers in the dorsolateral prefrontal cortex.

Spindle neurons are also called von Economo neurons (VENs), because Constantin von Economo provided the first comprehensive description of these neurons in 1925 (Seeley et al. 2012).  It was not until the end of the 20th century, however, that comparative neurologists began to study VENs as special neurons that might be part of what explains the evolutionary uniqueness of the human mind.

VENs appear in the brains of only a few species.  They are present in gorillas, bonobos, chimpanzees, and orangutans, although in numbers smaller than for humans.  They are also found in the brains of whales, dolphins, and elephants.  Thus, VENs are associated with species that have large brains, which suggests the possibility that VENs facilitate speedy communication of neural signals over neural networks scattered over large brains.  VENs are also associated with species that have complex social lives and that show mirror self-awareness (recognizing themselves in mirrors).  This supports the speculation that VENs allow animals to self-consciously navigate successfully through complex social interactions.  This fits with the "social brain hypothesis" of Robin Dunbar--the idea that the evolution of large and complex brains arose primarily as an adaptation for the mental challenges of social life (Allman et al. 2010; Bauernfeind et al. 2013; Cauda et al. 2014; Chen 2009; Craig 2015, pp. 217-19; Dunbar and Shultz 2007).  (I have written a post on Dunbar's presentation of his theory at the 2013 conference of the Mont Pelerin Society in the Galapagos Islands.)

Allman et al. (2010, pp. 496-97) have argued that the VENs in the anterior insula and anterior cingulate cortex are activated either by social error--by some defect in an individual's social network--or by social success--by some satisfying experience in a social network:

". . . For example, these structures are activated by resentment (Sanfey et al. 2003), deception (Spence et al. 2001), embarrassment (Berthoz et al. 2002), and guilt (Shin et al. 2000).  They are also activated by feelings of empathy for the suffering of others, another type of social error signal (Singer et al. 2004).  In mothers, FI in the right hemisphere responds to the crying of distressed infants (Lorberbaum et al. 2002), which is a powerful social error signal.  The anterior insula (including both superior and inferior components) was activated when partners in the prisoner's dilemma game failed to reciprocate cooperative moves made by the subject, which is a type of social error signal (Rilling et al. 2008).  Anterior insula and anterior cingulate cortex are also activated by pro-social signals, such as love and trust (Bartels and Zeki 2004; Singer et al. 2004), which suggests that these structures register both negative and positive aspects of the states of social networks.  The responses of FI and LA are parametrically related to how humorous subjects judge cartoons to be; the humorous content of the cartoons typically involved social errors (Watson et al. 2007)."

Here the VENs are associated with the moral emotions of social life such as guilt, shame, resentment, sympathy, love, and a sense of humor.

There are few VENs in human infants at birth.  The number of VENs increases rapidly during the first eight months of life, and they reach adult numbers at about four years of age.  The number is extremely variable between individuals, which might explain individual variability in the acuteness of self-awareness and social awareness (Allman et al. 2011).

Another way to infer the functional activity of VENs is to notice how the degeneration of VENs leads to distinctive kinds of mental disorders.  For example, early behavioral variant frontotemporal dementia arises from the degeneration of VENs in the anterior insular cortex and the anterior cingulate cortex.  People with frontotemporal dementia suffer a breakdown in their social character, showing a loss of self-conscious emotional control, social empathy, and emotional self-awareness.  They become insensitive, erratic, and irresponsible in ways that can destroy their social lives by breaking up their family lives and their professional careers.  This can be seen as additional evidence for seeing the evolution of VENs in humans as part of the evolution of the social brain (Kim et al. 2012).

Seeing people with severe forms of mental disorder like frontotemporal dementia is disturbing, because it raises the question of whether they have lost their souls, from having lost the neural activity that supports the self-awareness, social awareness, and moral sense that constitute the healthy human mind.

VENs seem to be a crucial part of that neural activity, and therefore the evolution of VENs must be part of the emergent evolution of the mind in the primate brain.

Some of my other posts on the evolution of the mind can  be found here, here, here, and here.

Most of the research that I have reported here relies heavily on brain imaging.  I have argued against the fallacy of seeing brain imaging as mind reading here, here, and here.


REFERENCES

Allman, John, et al. 2010. "The von Economo Neurons in Frontoinsular and Anterior Cingulate Cortex in Great Apes and Humans." Brain Structure and Function 214:495-517.

Allman, John, et al. 2011. "The von Economo Neurons in the Frontoinsular and Anterior Cingulate Cortex." Annals of the New York Academy of Sciences 1225:59-71.

Bartels, A., and S. Zeki. 2004. "The Neural Correlates of Maternal and Romantic Love." Neuroimage 21:1155-1166.

Bauernfeind, Amy L., et al. 2013. "A Volumetric Comparison of the Insular Cortex and Its Subregions in Primates." Journal of Human Evolution 64:263-79.

Berthoz, S., et al. 2002. "An fMRI Study of Intentional and Unintentional (Embarrassing) Violations of Social Norms." Brain 125:1696-1708.

Cauda, Franco, et al. 2013. "Functional Anatomy of Cortical Areas Characterized by Von Economo Neurons." Brain Structure and Function 218:1-20.

Chen, Ingfei. 2009. "Brain Cells for Socializing." Smithsonian Magazine, June 2009.

Craig, Arthur D. (Bud). 2015. How Do You Feel? An Interoceptive Moment with Your Neurobiological Self. Princeton, NJ: Princeton University Press.

Dunbar, Robin, and S. Shultz. 2007. "Evolution in the Social Brain." Science 317:1344-1347.

Kim, Eun-Joo, et al. 2012. "Selective Frontoinsular von Economo Neuron and Fork Cell Loss in Early Behavioral Variant Frontotemporal Dementia." Cerebral Cortex 22:251-59.

Lorberbaum, J.P., et al. 2002. "A Potential Role for Thalamocingulate Circuitry in Human Maternal Behavior." Biological Psychiatry 51:431-45.

Nimchinsky, E. A., et al. 1995. "Spindle Neurons of the Human Anterior Cingulate Cortex." Journal of Comparative Neurology 355:27-37.

Rilling, J., et al. 2008. "Neural Correlates of the Affective Response to Unreciprocated Cooperation." Neuropsychologia 46:1265-1266.

Sanfey, A. G., et al. 2003. "The Neural Basis of Economic Decision-Making in the Ultimatum Game." Science 300:1755-1758.

Seeley, William W., et al. 2012. "Distinctive Neurons of the Anterior Cingulate and Frontoinsular Cortex: A Historical Perspective." Cerebral Cortex 22:245-50.

Shin, L. M., et al. 2000. "Activation of Anterior Paralimbic Structures During Guilt-Related Script-Driven Imagery." Biological Psychiatry 48:43-50.

Singer, T., et al. 2004. "Brain Responses to the Acquired Moral Status of Faces." Neuron 41:653-62.

Spence, S. A., et al. "Behavioural and Functional Anatomical Correlates of Deception in Humans." NeuroReport 12:2849-2853.

Watson, K. K., et al. 2007. "Brain Activation During Sight Gags and Language-Dependent Humor." Cerebral Cortex 17:314-24.

The Emergent Freedom of the Mind in the Brain: A Reply to Stephen Craig Dilley

In the 2008 issue of the Journal of Interdisciplinary Studies, Stephen Craig Dilley--a philosopher at St. Edward's University--has an article on "Enlightenment Science and Globalization." He attacks my Darwinian conservatism because of its "Enlightenment claim that the laws of nature and material causes are sufficient to produce 'emergent' human minds capable of the kind of free will consistent with moral responsibility." The problem, he warns, is that this "implies determinism of the mind and the disintegration of morality."

In Darwinian Natural Right and Darwinian Conservatism, I have argued that the human mind or soul can be explained as a product of the emergent evolution of the brain. The evolution of the primate brain shows a trend towards increasing size and complexity of the neocortex, which allows for greater behavioral flexibility in these animals. This trend reaches its peak in the human brain. Larger and more complex frontal lobes give animals the capacity for voluntary action, in the sense that they can learn to alter their behavior in adaptive ways. In human evolution, the growth in the size and complexity of the frontal lobes passed over a critical threshold allowing human beings to use words and images to compare alternative courses of action through mental trial and error. Consequently, human beings are capable not just of voluntary action but of deliberate choice, by which they self-consciously choose present courses of action in the light of past experiences and future expectations to conform to some general plan of life.

Against this, Dilley develops two kinds of criticism. First, he complains that my account of the emergent evolution of the mind in the brain is too vague, because it does not explain the specific details of how exactly the evolution of the primate brain gives rise to the human mind. Second, he argues that since I never explain "how mental events and properties can transcend the limits of physical causation," but rather assume "the sufficiency of purely natural causes to account for all things in heaven and on earth," I must implicitly accept that all human actions are causally determined by material causes and natural laws. This assumption that all mental activity has natural causes leads to the "disintegration of morality," Dilley insists, because it denies the possibility of free will and thus denies that people can be held morally responsible for their actions.

To the first charge, I plead guilty. I don't provide a detailed explanation for exactly how the human mind arises from the evolution of the brain, because as far as I know, no one has yet worked out such an explanation. Lots of evidence points to the evolutionary history of the primate brain as passing over some kind of critical threshold at which fully human mental capacities appear. But it's hard to say how exactly that happens. Our situation is comparable to our ignorance prior to the 1950s of how exactly genes work. We knew a lot about the outcomes of these genetic mechanisms. But we didn't know exactly how these mechanisms worked. In fact, even today, genetics is still shrouded in great mystery. The same is true for explaining how human self-conscious thinking and willing arises in the brain as shaped by a history of genetic evolution. But even so, we can say that the evidence supports the general conclusion that the mind arises in the brain by some kind of natural causality.

Does Dilley have his own detailed explanation of how exactly the human mind originated? If he does, he does not lay it out it in this article. It's hard to know how to respond to his criticism of my account of the evolutionary emergence of mind, because he offers no alternative explanation of his own.

Similarly, it's hard to respond to his criticism of my account of human mental freedom, because he never explains his alternative. At one point, he complains that in my reasoning, "God, spiritual beings, or non-material causes are out of the picture." But then he never explains exactly how "God, spiritual beings, or non-material causes" create human mental freedom.

Against the Kantian account of moral freedom as freedom from nature, I argue that our moral experience requires a notion of moral freedom as freedom within nature. The uniqueness of human beings as moral agents requires not a free will that transcends nature--as Dilley seems to believe--but a natural capacity to deliberate about one's desires.

We hold people responsible for their actions when they act voluntarily and deliberately. They act voluntarily when they act knowingly and without external force to satisfy their desires. They act with deliberate choice when, having weighed one desire against another in the light of past experience and future expectations, they choose that course of action likely to satisfy their desires harmoniously over a complete life. Such deliberation is required for virtue in the strict sense, although most human beings most of the time act by impulse and habit with little or no deliberation.

Children and other animals are capable of voluntary action. But only mature human adults have the cognitive capacity for deliberate choice. Being morally responsible is not being free of one's natural desires. Rather, to be responsible one must organize and manage one's desires through habituation and reflection to conform to some conception of a whole life well lived. One must do this to attain the happiness of a flourishing life, which is the ultimate end of all human action.

I reject any contrast between free will and determinism as a false dichotomy. Moral freedom should be identified not as the absence of determinism but as a certain kind of determinism. We are free when our actions are determined by our deliberate choices. I doubt that we ever have any real experience of people acting outside the laws of nature. Moral judgment assumes a regular and predictable connection between what people desire and what they do. To hold people responsible for their actions, we must assume that their beliefs and desires causally determine their actions.

I reject the idea of free will as uncaused cause. I agree with Jonathan Edwards that whatever comes into existence must have a cause. Only what is self-existent from eternity--God--could be uncaused or self-determined. In fact, the very idea of free will as uncaused cause comes from the biblical conception of God, and so, as Martin Luther observed, "free will is a divine term and signifies a divine power." Against the absurd idea that human beings could have such a divine power of free will as uncaused cause, I would say--like Edwards--that the common-sense notion of liberty is the power to act as one chooses regardless of the cause of the choice.

So what is Dilley's alternative? It's not clear. He refers to "agent causes." He never explains what that means. But since he rejects my idea that in human choices, our beliefs and desires causally determine our actions, I can only infer that he is implicitly appealing to free will as uncaused cause.

If that's what he is doing, then I would respond to him as I have to Denyse O'Leary. Like O'Leary, Dilley seems to adhere to a Gnostic dualism that insists on an absolute separation of mind and body. This Gnostic scorn for the natural world as incapable of embodying spiritual freedom denies both Christian orthodoxy and common sense.

Is Dilley implying that we cannot explain the emergence of the human mind without invoking "God, spiritual beings, or non-material causes"? If so, could he explain how exactly this works? And could he explain why God was either unable or unwilling to create the human soul through natural evolution?

Thomas Aquinas's Neuroscience of the Soul

One of my graduate students--Paul Vasholz--is writing a dissertation that argues for the compatibility of free will with modern neuroscience. In developing his argument, he builds on the work of Walter J. Freeman, a neuroscientist who defends the reality of human freedom, while also showing how neuroscience supports Thomas Aquinas's philosophical psychology.

Freeman's research has led him to formulate what he calls "nonlinear brain dynamics" as an alternative to the linear causality that is assumed in much neuroscientific research. Moreover, he argues, this nonlinear brain dynamics supports Aquinas's teaching about the unity of mind, brain, and body. Freeman's position catches my interest, because it seems to sustain my argument about the emergent evolution of the soul in the brain and the freedom of the human soul as the product of that emergent evolution.

For Freeman, the key question is whether perception is passive or active. While Plato views perception as a passive acceptance of eternal forms or ideas, Aristotle views perception as an active exploration of the world. Aquinas follows Aristotle in explaining perception as an active process of assimilation. The body does not absorb stimuli, but rather it changes its own form to grasp those aspects of the stimuli that are relevant to the goals in the brain. Knowledge is not driven by external powers, as suggested by Plato, but rather knowledge is driven by the brain's internal strivings and ends, as we explore the world and, by trial and error, assimilate ourselves to our physical and social world in a manner that satisfies our desires.

But then where do these self-generated actions into the world--our strivings to search and observe the world--come from? Aquinas's answer is that the ultimate source of our striving is nature and nature's God. Freeman's answer is that the ultimate source is natural evolution. Through evolutionary history, human beings have inherited a natural set of desires or inclinations that guide their intentional behavior.

I agree with Freeman that there is much in Aquinas's philosophical psychology that supports this understanding of the emergent evolution of the soul or mind as the activity of the brain. But Freeman fails to confront the incoherence in Aquinas's reasoning on this point, which manifests a fundamental problem in Aquinas's Aristotelian science of human nature. This is not just a problem for Aquinas, but a general problem in reconciling Biblical religion and evolutionary science. (See Freeman's "Nonlinear Brain Dynamics and Intention According to Aquinas," pp. 211-12, 211, 230-31, 233.)

The problem is the incoherence in both affirming and denying a radical dualism of body and mind. On the one hand, Aquinas agrees with Aristotle's biological psychology that the mind is the form of the living body, and thus mind and body are inseparable, so that the death of the body is the death of the mind. On the other hand, Aquinas's commitment to the Christian teaching about the afterlife forces him to say that the human mind or soul is immaterial and thus capable of existing without the living body supporting it. The situation becomes even more confusing when we see that Aquinas's commitment to the Christian teaching about the resurrection of the body forces him to say that the human mind or soul cannot exist in its perfection unless it is the activity of a living body.

Aquinas recognizes that in adopting Aristotle's biological psychology, he has to reject Plato's dualistic psychology. For Plato, the immortal soul rules over the mortal body like a pilot of a ship, and thus the soul can live on after the death of the body. Many early Christians (like Augustine) saw this Platonic dualism as the closest pagan approximation to Christian theology. After all, Plato's dialogues offer elaborate arguments for the immortality of the soul in an afterlife with eternal rewards and punishments. Plato's Timaeus looks enough like Biblical creationism that it became the primary text for medieval Christian cosmology. And yet orthodox Christians cannot be Platonic dualists, because Christians must believe in the resurrection of the body in the afterlife, which suggests that the perfection of the soul depends on the body. Moreover, Aristotle's criticism of Plato's theory of the eternal Ideas, with its dualism of mind and body, and Aristotle's teaching that the mind is the functional activity of the body denies Platonic dualism.

To defend the doctrine of the resurrection of bodies to eternal life, Aquinas thinks he needs to reject Platonic dualism and embrace Aristotelian mind-body unity. But it's not at all clear that an Aristotelian biological psychology can allow for living bodies to become immortal. Moreover, traditional Christian doctrine teaches that there's a period between death and resurrection in which human souls exist without bodies, just as angels exist without bodies. But it's hard to see how this is reconcilable with the inseparable unity of mind and body.

Aquinas is thus caught in a contradiction. He must say that "the soul is the form of the animated body," and "forms dependent in being upon matter do not themselves have being properly, but being properly belongs to the composites through their forms" (Summa Contra Gentiles, II, 51, 57). This would be compatible with neuroscientific research showing that the mind is the emergent activity of the brain. But then Aquinas also says that the human mind is an immaterial form that is not necessarily the form of a living material body. This suggests a radical dualism contrary to neuroscience.

The confusion is deepened, however, when Aquinas teaches that since "the soul is united to the body as form to matter," the perfection of the soul after the death of the body requires a resurrection of the body and its reunion with the soul. Thus must be so, because "the state of the soul in the body is more perfect than outside the body" (Summa Theologica, suppl., q. 75, a. 1).

Furthermore, according to Aquinas, this resurrected body must be a real living body. And since all living bodies are ageing bodies, the resurrected bodies must have a specific age. Since Jesus rose again at about age 30, that age must be the perfect age for the body, and so, Aquinas reasons, when human beings are resurrected, they will all have bodies of the same age--30 years old. Those who died as children will be moved up to age 30, and those who died in old age will be moved back to age 30 (ST, suppl., q. 81, a. 1).

But then we must wonder, when people wish for immortality, is this what they're wishing for--to be frozen eternally at one moment in time?

Shouldn't we say that this kind of immortality would be death?

Some related posts can be found here, here, here, here, here, here, here, here, here, here, here, and here.

Spinoza's Neurobiology: The Emergence of the Mind in the Body and the Brain

The human mind is the idea of the human body.

This assertion by Spinoza in his Ethics (particularly, part 2) can be judged as a claim about human biology open to confirmation or falsification by recent research in neurobiology.  If this is so, then this illustrates a point that I have often argued on this blog--that the history of political philosophy is largely a history of debatable empirical claims about human nature, social life, and the natural world generally that can be interpreted and assessed in the light of modern scientific knowledge.

Some folks might object that Spinoza is speaking as a philosopher, who appeals to logic and intuitive judgment, rather than as a biological scientist, who relies on hypothesis-testing through empirical research.  But this modern distinction between philosophy and science was not accepted in Spinoza's time, when what we today would call "natural science" was called "natural philosophy."  Beginning in ancient Greece, philosophers like Aristotle engaged in biological research.

Moreover, Spinoza indicated that his understanding of the relationship between the mind (mens in Latin) and the body (corpus) depended on his understanding of the brain (cerebrum).  Our thoughts arise in our brains as stimulated by the motions that our bodily nerves receive from objects outside of us and from the internal activities of our bodies (Ethics I, appendix).  Spinoza took seriously Descartes's research on human anatomy and physiology; and although he rejected Descartes's claim that the pineal gland is the place in the brain where mind and body meet, and although he saw this as contradicting Descartes' assumption that that mind and body are two distinct substances, he assumed that thought must arise somehow and somewhere in the brain (V, pref.).  Spinoza thus left open the possibility that increasing knowledge of the brain might reveal how mind emerges in the brain from its integration of signals from the body, which would explain the neural basis for what he saw as the parallelism of mind and body.

Indeed, Antonio Damasio has argued, in Looking for Spinoza, Spinoza's intuition that the mind is the activity of the body is confirmed by modern neurobiological evidence that "mental processes are grounded in the brain's mappings of the body, collections of neural patterns that portray responses to events that cause emotions and feelings" (12).

This Spinozistic claim that our conscious feelings arise from neural mappings of body states can now be experimentally tested.  For example, Damasio and his colleagues have hypothesized that when feelings occur, there is increased neural activity in those areas of the brain that receive signals from the body and thus map the ongoing state of the body.  These brain areas are at different levels of the central nervous system, which include several nuclei in the brain stem tegmentum (the back part of the brain stem), the hypothalamus, two of the somatosensory cortices (the insula and the secondary somatosensory cortex), and the cingulate cortex.

To test this hypothesis, Damasio and his colleagues recruited forty people with no history of neurological or psychiatric disease.  The subjects were asked to think of some intense emotional episode from their lives that involved happiness, sadness, fear, or anger.  They were in a brain scanning room so that machines could measure blood flow in their brains using the technique of PET (positron-emission tomography), with the understanding that increased blood flow to some region of the brain is correlated with the local activity of the neurons.  The subjects were asked to signal with a hand movement the moment they began feeling the emotion--happiness, sadness, fear, or anger.  The brain scans showed increased activity in the predicted areas of the brain, which indicated that the mapping of body states had been modified during the process of conscious feeling.

Apparently, what was happening is that in the past, body states had induced a feeling like anger in the brain, and then this experience had been stored in memory; so that when they recalled this memory of anger to recreate the feeling of anger, they activated the neural circuitry of the body-sensing brain regions associated with this feeling.

Here, then, Damasio concludes, we can see in these brain images the correlation of mind and body claimed by Spinoza.

Damasio's use of brain imaging to support this kind of argument is illustrated in this TED talk:

There are, however, at least three problems with Damasio's use of neurobiology to support Spinoza: the mystery of subjectivity, the self-refuting character of materialist science, and the experience of spirituality.

In his TED talk, Damasio passes over the mystery of subjectivity in two sentences about two minutes into the talk.  He says that many people, including many neuroscientists, have said that human self-consciousness is too mysterious to be explained scientifically.  He rejects this.  But then he says: "It would be ridiculous to claim that we know how we make consciousness in our brains. But we can begin to approach the question and to see the shape of an answer."  Here he is pointing to what he calls the "consciousness puzzle" in Looking for Spinoza (198).  We can see neural patterns through the "tools of neuroanatomy."  And through the "tools of introspection," we can subjectively see our own mental images or ask other people to report their mental images to us.  But we cannot see the process by which observable neuroanatomy creates subjective introspection.  We see correlation but not causation.

In his experiment with the 40 people asked to create feelings of happiness, sadness, fear, and anger, he could see the PET brain images, but he could not see their conscious feelings, because he had to rely on the people to report to him what they were feeling.

In his book, Damasio admits that there is a "knowledge gap" here (208).  He observes:

"The mind level of biological phenomena has additional specifications that are not present at the neural-map level.  I hope a reductionist research strategy eventually will allow us to explain how we get from the 'neural-map' level to the 'mental' level, although the mental level will not 'reduce to' the neural-map level because it possesses emergent properties created from the neural-map level.  There is nothing magic about those emergent properties, but there is a lot that remains mysterious, given our massive ignorance of what they may involve" (325).

As I have indicated in my posts on the evolutionary emergence of the mind in the brain, I agree that there is nothing magic here, but I also agree that there is some mystery as long as we cannot explain exactly the natural process by which the observable brain causes the subjective mind.

The biblical creationist might say that the only way to resolve this mystery of consciousness is to see that the conscious human mind is the creation of God in His image.  But as I have indicated in another post (here), this falls into the fallacy of explaining a mystery through an even greater mystery.

The second problem for Damasio's Spinozist neurobiology is the possibility that any materialist science that sees the human mind as the product of mindless evolution becomes self-refuting.  (I have written about this here.)  Damasio never recognizes this problem.

One of the best arguments for theism is that the theistic doctrine of the human mind as created by God in His image provides the necessary support for believing in the validity of human thought, including the validity of modern science. If we embrace Naturalism--the view that nothing exists except Nature, and so there is no transcendent Creator God--we are caught in self-contradiction: if human thought originated not from a divine Mind but from the irrational causes of Nature, then we cannot trust our minds as reliable, and thus we cannot trust our belief in Naturalism. Naturalism destroys itself by destroying the rationality of believing in Naturalism, or anything else. Insofar as science--including evolutionary biological science--depends on the validity of human thought, and insofar as theism is the indispensable support for trusting in the validity of human thought, science is not only compatible with theism, science depends upon theism.

Natural selection rewards adaptive behavior and punishes maladaptive behavior. But natural selection does not care about the truth or falsity of an animal's beliefs. If beliefs produce adaptive behavior, they will be rewarded by natural selection regardless of whether the beliefs are true or false. Therefore, the evolution of adaptive behavior in our prehistoric ancestors did not guarantee or make it probable that our cognitive faculties would be reliable in generating mostly true beliefs.  Even Damasio admits that as produced by evolution, the brain is not a passive mirror of objective reality, because it constructs its own images of the world to serve the evolved purposes of survival and reproduction (199-209).

The weak link in this reasoning, however, is the assumption that adaptive behavior is completely unrelated to true belief. On the contrary, the evidence of evolutionary history suggests that evolution produces cognitive faculties that are reliable but fallible. The mental abilities of animals, including human beings, are fallible because evolution produces adaptations that are good enough for survival and reproduction but not perfect, and this results in the mental fallibility that is familiar to us.

Despite this fallibility, the mental faculties cannot be absolutely unreliable. In the evolution of animals,adaptive behavior requires accurate indicators. So, for example, a frog must have sensory equipment that allows him to accurately detect flies so that he can catch them with his tongue.  The waggle dance of bees must convey accurate information to other bees. Similarly, the immune system of the human body must accurately indicate the presence of foreign bodies and then accurately devise responses to destroy the invaders.

For those animals who develop some capacity for conscious reasoning--and most preeminently human beings--the accuracy of this conscious reasoning will be important for adaptation. The highest mental capacities of human beings are so biologically expensive in terms of the investment of energy they consume that it is implausible that evolution would have produced them unless they improved the ability of human beings to track the truth about themselves and their environment. Again, this is going to be fallible, but it's implausible that human beings could be naturally evolved for being in a state of complete and perpetual delusion.  These reliable but fallible cognitive capacities can then be appropriated for scientific research, which must include methods to minimize those evolved biases that impede our accurate perception of the world, an important theme for Spinoza.

The third problem for Damasio's Spinozist neurobiology is whether it can account for and satisfy the human need for spirituality and religious salvation.  Damasio does recognize this problem (267-89).

If Spinoza is right about the essence of human nature being the natural striving for self-preservation, then we might expect that when we confront the reality of suffering and death, we naturally strive to escape that vulnerability and mortality in achieving some enduring if not eternal joy in our lives and the lives of those we love.  Our striving for self-preservation becomes a striving for salvation.

Spinoza identifies two ways to human salvation--one for the many common people (the vulgus), and the other for the philosophic few.  For the common people, salvation can come only through faith in biblical revelation:

". . . I judge the utility, even necessity, of Sacred Scripture, or revelation, to be very great.  We can't perceive by the natural light that simple obedience is a path to salvation.  Only revelation teaches that this happens, by a special grace of God, which we cannot grasp by reason.  It follows that Scripture has brought great comfort to mortals.  Everyone, without exception, can obey.  But only a few (compared with the whole human race) acquire a habit of virtue from the guidance of reason alone.  So, if we didn't have this testimony of Scripture, we would doubt nearly everyone's salvation" (TPT xv.44).

For this reason, Spinoza did not want common people to read his books, because this would do them no good (TTP, pref. 34).  He wrote his books in Latin and discouraged any translations into Dutch, because he wanted to be read only by those few learned people who could read Latin.

The philosophic few could not take the first way to salvation, because they accepted the truth of human mortality, and thus they could not believe in salvation through resurrection to eternal life with God.

For the philosophic few, there was a second way to salvation--what Spinoza at the end of The Ethics called  "the mind's intellectual love of God," which induces that fullest satisfaction of the mind that is felt as Joy, and which is eternal (V, prop. 34-42).  When I first read The Ethics in Cropsey's class, I struggled to understand what this means.  I still do.

If atheism is the denial of the existence of God or of anything divine, then Spinoza was not an atheist, because he does affirm the existence of God (Ethics I, p. 11). Spinoza denied the common charge that he was an atheist.

But if atheism is denial of the existence of a personal God, who cares for human beings, who listens to prayers, who reveals Himself miraculously to human beings, who demands obedience to His law, and who rewards and punishes human beings in an eternal afterlife, then Spinoza was an atheist.

One can say for sure that Spinoza's God is an absolutely infinite being that is the first cause--the uncaused cause--of all things, that it is a being that human beings can love, and that this love of God is the greatest human good, although in loving God, human beings cannot expect God to love them in return.

Spinoza's phrase "God or Nature" (Deus sive Natura) has led some people to say that Spinoza is a pantheist who identifies the whole universe as divine (IV, pref., p. 4).  But then Spinoza says that God as first cause is to be identified with "nature naturing" (Natura naturans) rather than "nature natured" (Natura naturata) (I, p. 29).  And yet he also says that he does not separate God from nature as other philosophers do (letter 6).  (Is "Nature's God" in the Declaration of Independence Spinoza's God?  I have written about this here.)

Spinoza seems to be affirming a secular or naturalistic religiosity based on a religious feeling of awe, love, or joy in contemplating the order of nature, but without any sense of a personal God.  As Damasio indicates, this was most powerfully affirmed by Albert Einstein, who said that his God was Spinoza's God.  He described the religious feeling of the "profounder sort of scientific minds" as taking "the form of a rapturous amazement at the harmony of natural law, which reveals an intelligence of such superiority that, compared with it, all the systematic thinking and acting of human beings is an utterly insignificant reflection."  He described this feeling as "a sort of intoxicated joy and amazement at the beauty and grandeur of this world, of which man can form just a faint notion.  This joy is the feeling from which true scientific research draws its spiritual sustenance, but which also seems to find expression in the song of birds."  This might be what Spinoza meant by amor intellectualis Dei.

And what can a neurobiologist like Damasio say about this?  At the very least, he observes, "the spiritual is a particular kind of feeling state. . . . a particular state of the organism, a delicate combination of certain body configurations and certain mental configurations" (286).

But if Spinoza is right, these religious feelings in the brain do not point to any transcendent reality beyond nature.

In my copy of the Elwes translation of Spinoza's Ethics that was the text for Cropsey's class, I wrote this note in the margin of the text for Part 5, proposition 30: "On the intellectual love of God, compare Lucretius: 'it is true piety to be able to contemplate all things with a calm mind' (5.1205)."

Is that enough for our salvation--at least for those few like Einstein who can feel joy in contemplating the beautiful order of a natural world that is joyful in being intelligible to our minds, although it does not care for or about us, so that we can love it without expecting to be loved in return?