Darwinian Conservatism Supports Emergent Complexity and Immanent Teleology: A Response to Robert Koons

The Darwinian conservatism of the permanent things requires a biological teleology of human nature.  Because one needs to claim that evolved human nature is directed to certain ends or goals that constitute the natural norms (the permanent things) of human existence, so that the fulfillment of those norms can be understood as the human good.

By contrast, the metaphysical conservatives argue that modern science--and particularly Darwinian biology--denies teleology in denying that human beings can have natural ends.  The metaphysical conservatives claim that for modern science, all reality is understood to be nothing but the blind motion of particles in space governed by material and mechanistic laws of motion; and in such a world, there can be no final causation.  At the Kirk Center conference, that claim was made by Robert Koons (University of Texas at Austin) on a panel on "Conservatism and Religion."

Koons said this as part of his general argument that modern science has been "mostly a very bad thing."  On this point, he saw himself as agreeing with C. S. Lewis in The Abolition of Man that "modern science was born at an inauspicious hour and in an unhealthy neighborhood."

I saw two problems in Koons' presentation.  First, he identified modern science with a reductionistic physics, and he was silent about the emergent complexity of biology.  Second, in arguing that modern science rejects teleology, he ignored the distinction between cosmic teleology and immanent teleology.

EMERGENT COMPLEXITY IN DARWINIAN BIOLOGY

In my chapter on "Emergence" in Darwinian Conservatism, I argue for the "emergent evolution of the soul in the brain," and I defend the idea of emergence as an alternative to both reductionism and dualism. As I have argued in previous posts, the simplest expression of the idea of emergence is that the whole can be greater than the sum of its parts. Emergent phenomena are those complex wholes with properties that we could not explain or predict from our knowledge of the parts. For example, when hydrogen and oxygen combine chemically to form water, we see emergent properties in water that we could not have predicted from the properties of hydrogen and oxygen. This emergence of novelty is manifested throughout the evolution of the universe. As we pass through levels of complexity, we find new properties at higher levels that are not fully reducible to the lower levels. This idea of emergence denies strong reductionism, because it denies that the higher levels of organization can be completely reduced to the lower levels. But the idea of emergence also denies dualism, because it denies any radical separation of matter and mind.

In his Descent of Man, Charles Darwin recognized--if only implicitly--that human beings show an emergent difference in kind from other animals.  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" (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 expansion 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.

Now we know from the work of neuroscientist Suzana Herculano-Houzel that human beings are unique as compared with other primates in that human beings have 16 billion neurons in the cerebral cortex, which includes 1.3 billion in the prefrontal cortex.  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, we can now identify that critical threshold as the remarkably large number of neurons in the human cerebral cortex and particularly in the prefrontal cortex.  That probably explains the three points of human uniqueness that Darwin saw--self-conscious awareness, morality, and language.

Koons is silent about this emergent complexity of human biology in asserting that all of modern science must reduce reality to the motion of particles in space.

IMMANENT TELEOLOGY IN DARWINIAN BIOLOGY

Koons is also silent about how Darwinian biologists recognize the immanent teleology of living beings even though they deny the cosmic teleology of the universe.  In insisting that modern science denies teleology, Koons has to assume that cosmic teleology is the only kind of teleology.  And thus he ignores the fact that for Aristotle natural teleology was more clearly biological than cosmological.

As I have argued previously, Darwin recognized the teleological character of his evolutionary science.  In an article in Nature, Asa Gray wrote: "let us recognize Darwin's great service to Natural Science in bringing back to it Teleology; so that instead of Morphology versus Teleology, we shall have Morphology wedded to Teleology."  In response to this, Darwin wrote to Gray (June 5, 1874): "What you say about Teleology pleases me especially and I do not think anyone else has ever noted that."  So, we can infer, that when Darwin read Aristotle's explanation of biological teleology in the Parts of Animals and expressed his admiration for Aristotle's biological science, Darwin saw that he really was bringing back into science a teleological conception of living nature that was originally formulated by Aristotle.

We need to see that while Darwin denied cosmic teleology, he affirmed immanent teleology. The natural evolution of living beings does not conform to any cosmic design. But that natural evolution does produce species that show an internal teleology in being directed to ends or goals. For example, a mammalian species is naturally adapted for parental care, so that mothers caring for their offspring can be explained teleologically as goal-directed behavior. Such species-specific, immanent teleology is the only kind of teleology that Aristotle saw in the living world, and modern biology confirms such Aristotelian teleology.

Insofar as Darwinian biology allows for emergent complexity and immanent teleology, this is enough for a Darwinian conservatism.

Roger Scruton's Fallacious Argument in "On Human Nature"

In his new book On Human Nature (Princeton University Press), Roger Scruton shows the straw man fallacy in criticizing the biological science of human nature as biological reductionism.  Although some biologists do sometimes sound like absolute reductionists, most biologists--beginning with Charles Darwin himself--recognize that any biological science of human nature must explain the emergent differences in kind between human beings and other animals, for which there is no fully reductionist explanation. One needs to see, however, that these emergent differences in kind are not radical differences in kind that would require some creationist or Kantian metaphysics of transcendence.

In The Descent of Man (Penguin Classics, 2004), Darwin did seem to be a reductionist when he declared that the differences between human beings and the other animals was only a difference in degree and not in kind:

"Some naturalists, from being deeply impressed with the mental and spiritual powers of man, have divided the whole organic world into three kingdoms, the Human, the Animal, and the Vegetable, thus giving to man a separate kingdom.  Spiritual powers cannot be compared or classed by the naturalist: but he may endeavor to shew, as I have done, that the mental faculties of man and the lower animals do not differ in kind, although immensely in degree. A difference in degree, however great, does not justify us in placing man in a distinct kingdom" (173).

Against this apparent reductionism, Scruton argues that human beings are irreducibly different in kind from other animals: "We are animals certainly; but we are also incarnate persons, with cognitive capacities that are not shared by other animals and which endow us with an entirely distinctive emotional life--one dependent on the self-conscious thought processes that are unique to our kind" (29-30).

Other animals are conscious, Scruton contends, but only human beings are self-conscious in being able to say "I," who thus become persons rather than mere objects.

Other animals can communicate, but only human beings have language, which allows them to tell stories about themselves and their world; and thus they can live in imagined symbolic worlds that they have created for themselves, which includes the religious symbolism of stories about the divine.

Other animals are social beings who can enforce rules of social cooperation, but only human beings have a moral sense by which they judge the conduct of themselves and others as right or wrong, good or evil, just or unjust.

Scruton concedes that all of these distinctively human traits depend upon biological capacities in the brain that are objectively observable and thus open to scientific explanation.  And yet, he argues, the uniquely human experiences of self-conscious awareness, understanding language, and moral judgment are inward subjective experiences of the mind that cannot be outwardly seen through objective observation, and therefore they cannot be studied by the natural science of biology.

In all of this, Scruton assumes a fundamental dualism that originated in nineteenth-century Romanticism, which is conveyed in Wilhelm Dilthey's separation of Geisteswissenschaften (human sciences or sciences of the mind or the humanities) and Naturwissenschaften (natural sciences) (12, 22-23, 46).  The natural sciences seek causal explanations of the objectively observable realm of Nature.  The humanities seek interpretive understanding of the subjectively experienced realm of Spirit or Mind, which is the uniquely human realm.  This kind of distinction is assumed in the way academic disciplines are organized in Western culture: the natural sciences and social sciences are separated from the humanities.

Scruton illuminates this distinction through an analogy (30-32).  When painters paint on a canvas, they create physical objects by physical means.  When we look at the painting, we are looking at the physical blobs of paint on the physical canvas.  But if we see a face in the painting, the face is in some manner something more than the physical blobs of paint.  Seeing the face is a subjective experience in our inward mental experience.  Natural science can explain the physical and chemical properties of the painting as objectively observable phenomena.  But our subjective awareness of the face is an inward mental experience that cannot be reduced to the physical and chemical properties of the painting.  Similarly, we might say that persons are to their bodies as seeing the face in the painting is to the physical blobs of paint on the canvas. 

Personhood is an emergent feature of the human organism that depends on the biological capacities of the organism but without being fully reducible to those biological capacities.  The brain scientist can explain the natural physical and chemical properties of the brain that make personal subjectivity possible, but this cannot fully explain the subjective experience to which a person has direct access, but which is invisible to the scientific observer.  We can design machines that paint pictures, but we cannot assume that those machines see faces in their pictures.  Thus, the human person is an emergent entity rooted in the human animal body but belonging to a higher realm of reality beyond biology.

Emergence occurs when quantitative differences pass over a critical threshold of complexity to become qualitative differences: differences of degree become differences in kind.  So, for example, with rising temperature, ice becomes water, and then water becomes steam.  Scruton concludes: "What we are trying to describe in describing personal relations is revealed only on the surface of personal interaction.  The personal eludes biology in just the way that the face in the picture eludes the theory of pigments.  The personal is not an addition to the biological: it emerges from it, in something like the way the face emerges from the colored patches on a canvas" (41).

The straw man fallacy in Scruton's argument is in his false assumption that biologists must be reductionists who fail to see the need for the idea of emergence as part of their scientific explanation of subjective mental experience.  In fact, as I have argued in various posts (here, here, here, and here), many biologists, beginning with Darwin, have recognized biological emergence.

That Scruton is attacking a straw man becomes evident as soon as one notices that Scruton's example of a painting as illustrating emergence is used in exactly the same way by some scientific naturalists--such as the physicist Sean Carroll in his recent book The Big Picture (pp. 94-95).

Despite Darwin's explicit statement that humans differ only in degree, not in kind, from other animals, he implicitly recognized all the differences in kind that are stressed by Scruton.  That is to say, that Darwin recognized that human beings have some 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" (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 expansion 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.

Scruton agrees with this in that human uniqueness emerges from small steps in evolution without any need for positing some separate miraculous origin for human beings: there is "no impassible gap" (66).

Scruton and Darwin also agree about what Scruton calls "the mystery of the subjective viewpoint" (135).  We can see the body through outward observation.  But the mind is invisible, and we can know it directly only by our own inward experience of mental awareness; and therefore we can only infer mental experience in other human beings or other animals by interpreting their outward movements as evidence of inward subjectivity similar to our own.  So, as Aquinas said, "the internal passions of animals can be gathered from their outward movements."

Darwin recognizes "the impossibility of judging what passes through the mind of an animal" (105).  But he believes that scientists can make reasonable inferences about the invisible subjectivity of animal minds from careful observation of their bodily movements and bodily expression of emotions. And, of course, this is what ethologists do when they infer animal psychology from observational and experimental studies of animal behavior.  Ethologists thus engage in scientific "mind reading."  And, as we have seen in some posts (here), some ethologists see experimental evidence for other animals having a "theory of mind," so they read the minds of other animals.  Oddly, Scruton ignores this when he asserts that interpreting animal minds is not part of science, but belongs only to the humanities and to ordinary folk psychology.

Scruton also ignores the scientific study of what Darwin called the "mental individuality" of animals (Darwin, 106), which includes the study of "animal personality" (a topic for various posts here and here).  Scruton does admit that other animals show "shallow individuality," although he insists that only human beings show "deep individuality" (80-82).

And while Scruton denies that other animals have morality, he does admit that apes show "near equivalents of punishment, appeasement, and reconciliation" (84).

If it is possible for biological scientists to study the mind--the Geist--then they can study those uniquely human traits that arise through mental subjectivity--self-consciousness, morality, and language--and thus biology can account for the fullness of human nature as including both body and mind.  If this is true, then biology includes the Geisteswissenschaften as well as the Naturwissenschaften.

And this biological study of human psychology includes the biological study of religious psychology as rooted in the evolved human propensity for detecting intelligent agency: just as we read the invisible minds of other human beings and other animals, we read the invisible mind of God.  Our natural desire for religious understanding is rooted in our natural desire for understanding invisible minds.  Evolutionary psychologists can agree on this without agreeing on whether this religious psychology points to the real existence of a divine mind, which has come up in posts (here).

In his affirmation of atheistic religiosity, Scruton affirms religious longing as part of human nature grounded in evolved human psychology, but without affirming the doctrinal truth of that natural religion.

Scruton's atheistic but religious conservatism resembles the position of other conservatives such as Peter Augustine Lawler, who have tried to argue that evolutionary science provides a true, but only partially true, account of human nature.  (My post here on Lawler includes links to many others on our friendly debates.)

Like Scruton and Lawler, Leon Kass is another conservative thinker who attacks the straw man of Darwinian biology as crude reductionism.  I have responded to Kass in previous posts here and here.

Their mistake is in refusing to see how Darwinian biology can recognize the whole truth about evolved human nature as showing both continuities with and emergent differences in kind from other animals.

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.

The Darwinian Emergence of Aristotle's Political Animals and de Waal's Moral Animals: A Reply to Cheryl Abbate

In various publications (Arnhart 1990, 1994, 1998, 2009), and in some blog posts, I have argued that a Darwinian science of animal behavior can support Aristotle's biological science of political animals.  Aristotle's statement that "man is by nature a political animal" is famous.  But it is often falsely assumed to mean that human beings are by nature the only political animals.  As Aristotle explains in his biological writings, the political animals include ants, bees, wasps, and cranes.  But even if humans are not the only political animals, Aristotle indicates, they are distinctive in that they are more political than the other political animals, because humans have a biological capacity for logos, which allows them to organize their political communities through shared symbolic conceptions of justice.

In his biological works, Aristotle sees that some animals are solitary and others gregarious.  Of the gregarious animals, some are political.  Some of the political animals have leaders, but others do not.  The distinguishing characteristic of the political animals is that they cooperate for some common work or function.  Humans, bees, ants, wasps, and cranes are all political animals in this sense.

The uniquely human capacity for speech or rhetorical persuasion makes humans more political than the other political animals, because while other animals can share their perceptions of pleasure and pain, humans can use speech to share their conceptions of the advantageous, the just, and the good.  Through speech, humans cooperate for common ends in ways that are more complex, more flexible, and more extensive than is possible for other animals.  Through speech, humans can deliberate about the common interest as the standard of justice.  A just political community can be judged to be one that serves the common interest of all or most of its members, as contrasted with an unjust political community that serves only the private interest of its ruling group.

I have argued that Charles Darwin's evolutionary theory of morality and animal social life supports Aristotle's biopolitical science.  I have also argued that the biological study of animal behavior over the past 60 years (beginning with Jane Goodall's arrival at the Gombe Stream Preserve in 1960) has largely confirmed this Aristotelian science of animal politics.

Recently, I noticed that Cheryl Abbate (2016) has disagreed with my reasoning in what is essentially a critique of my 1990 article in Social Science Information.  I also noticed that Edward Jacobs (2018) has written a response to Abbate's article, and Abbate (2018) has replied to him.

Abbate's critique consists of two arguments.  First, she claims that my defense of Aristotle's teaching contradicts the Darwinian principle of the psychic continuity between humans and animals--the idea that humans differ from other animals only in degree and not in kind.  Second, she claims that recent studies of animal behavior show that some highly social nonhuman animals have a sense of justice, and so Aristotle is wrong in thinking that this is unique to human beings.

As you might expect, I believe she's mistaken on both points.

DARWIN ON EMERGENT DIFFERENCES IN KIND

Abbate correctly quotes from the crucial passage in Aristotle's Politics (1253a) where Aristotle declares that a human is much more a political animal than other political animals, because "man alone among the animals has speech [logos]," and through speech, "he alone has a perception of good and bad and just and unjust," which is the uniquely human basis of human politics (Abbate 2016, 57).

She then claims that this contradicts the Darwinian principle of "evolutionary continuity"--that all differences between species are only differences in degree and not in kind (Abbate 2018, 160).  She correctly quotes from Darwin's apparent endorsement of this idea in The Descent of Man:

"Nevertheless, the difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind.  We have seen the senses and intuitions, the various emotions and faculties, such as love, memory, attention, curiosity, imitation, reason, etc., of which man boasts, may be found in an incipient, or even sometimes in a well-developed condition, in the lower animals" (2004, 151).

Abbate is silent, however, about the fact that despite Darwin's explicit statement that humans differ only in degree, not in kind, from other animals, he implicitly recognized human differences in kind.  That is to say, Darwin saw that human beings have some moral and mental traits that other animals do not have at all.

In The Descent of Man, 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" (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 was thrown into self-contradiction--both affirming and denying that humans are different in kind from other animals--because he failed to see how he could affirm emergent differences in kind without affirming any radical differences in kind.  Emergent differences in kind can be explained by evolutionary 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 development of the primate brain, so that at some critical point in the evolution of our hominid 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 primate ancestors, so there is no need to posit some supernatural intervention in nature--the divine creation of the human soul--that would create a radical difference in kind in which there is a gap with no underlying continuity of natural causes.

Edward Jacobs points to this when he describes the evolution of the human mind.  "The moment a certain threshold of mental development was reached (and logos is as good a placeholder name for this threshold as any), we became able to make and grasp persuasive accounts," which made humans more political than the other political animals (155).

Simona Ginsburg and Eva Jablonka (2019) have shown how an evolutionary neuroscience could explain this emergence of the human mind as passing through the three levels of mind identified by Aristotle in De Anima (On the Soul). The basic nutritive and reproductive soul belongs to all living things--plants and animals.  The second level--the sensitive soul--belongs to all animals.  The third level--the rational or symbolizing soul--is specific to humans.  The crucial evolutionary transition marker of the rational soul is language.  The rational soul gives humans the capacity for grasping and sharing the abstract symbolic values of the good and the just that make human politics unique.  Ginsburg and Jablonka suggest that all three levels can be explained by evolutionary biology.

I have written some previous posts on emergent evolution (here and here).;

BEKOFF AND DE WAAL ON THE MORAL LIVES OF ANIMALS

Abbate relies heavily on two cognitive ethologists--Marc Bekoff and Frans de Waal--for providing the evidence that some nonhuman animals have a sense of justice, and therefore Aristotle is wrong in saying that humans alone have a moral sense, which makes them more political than the other political animals.  For Abbate, this proves that humans differ only in degree, not in kind, from other animals.

Bekoff is best known for his studies of canid social carnivores--wolves, dogs, and coyotes--and his argument that their social play shows that they have "codes of conduct" that indicate a moral life of "wild justice" (Bekoff 1995; Bekoff and Pierce 2009; Pierce and Bekoff 2012).

De Waal is best known for his Chimpanzee Politics and other studies of primate colonies in captivity.  He has endorsed what he calls my "Darwistotelian" view of human politics and morality as showing an evolved political nature shared with chimps and other primates. A sample of my many posts on de Waal can be found here, here, here, here, and here.

She does not notice, however, that Bekoff and de Waal show the same self-contradiction that one can see in Darwin.  On the one hand, Bekoff says that "animal morality is different in degree but not in kind from human morality."  On the other hand, he says there are "bona fide differences in kind" (Bekoff and Pierce 2009, 139-40).  He admits that "human morality is unique," because humans are unique in their capacities of language and judgment (Bekoff and Pierce 2009, 132, 139-42).  Similarly, de Waal sometimes seems to say that morality is not unique to human beings, but then he concedes that morality at the level of judgment and reasoning is uniquely human (de Waal 2006, 20, 173-75).

Abbate might say, however, that this is not necessarily contradictory.  If de Waal is right about there being three levels of human morality, and if nonhuman animals show some elements of the lower levels but not of the higher levels, then the fullest expression of human morality is uniquely human, although some animals show some features of the moral life.  Thus, there is both continuity and discontinuity in the moral psychology of animals.  At some levels of morality, there is only a difference in degree.  At other levels, there is a difference in kind.  This is exactly what one would expect from the emergent evolution of animal morality.  And, I suggest, this is Aristotle's position, even though his biology did not have a fully developed evolutionary theory.

According to de Waal, the moral sentiments constitute the first level of morality--the emotional building blocks of morality that include empathy, reciprocity, retribution, a sense of fairness, and reconciliation to resolve conflicts and restore harmonious relationships (de Waal 2006, 166-75).  All of this can be seen in some form in other animals

In stressing the importance of the moral sentiments for moral psychology, de Waal belongs to the philosophic tradition of sentimentalist ethics that includes David Hume, Adam Smith, Darwin, and Edward Westermarck--a tradition that is set against the Kantian tradition of rationalist ethics.  I have written many posts on this, including here, here, here., and here.

De Waal identifies social pressure as the second level of morality.  Through social pressure, individuals are habituated to conform to the social rules of their group that maintain the good order of the community.  These rules are enforced through reward, punishment, and reputation.  In these ways, morality serves as a social contract for a cooperative society. Some of this can be seen in some nonhuman animals.  For example, high-ranking males in chimpanzee groups show "policing behavior"--males break up fights among others, and their intervention seems to be remarkably evenhanded.  Nevertheless, the human morality of social pressure goes beyond animal morality by formulating social rules that are more abstract and systematic than is the case for other animals.

Finally, judgment and reasoning constitute a third level of morality, and this is uniquely human.  So, for example, we are like other social animals in that we care about our reputations--how we appear in the eyes of others--so that we want to be praised and not blamed by others; but we can also use our distinctively human capacity for abstraction and imagination to see ourselves mirrored in the eyes of an "impartial spectator" (as Adam Smith said), so that we can want to do what is praiseworthy, regardless of whether we are actually praised by anyone. We care not only about our real reputation but also about our imaginary reputation.  From this we develop an internal sense of self-esteem or conscience.  There is no evidence for anything like this in nonhuman animals.  (I have written about Smith's concept of the "impartial spectator" here.)

Like de Waal, Aristotle saw both continuity and discontinuity between human beings and other animals in their moral psychology.  In his History of Animals (588a15), he wrote:

"In most of the other animals, there are traces of the qualities of soul that are more evidently differentiated in human beings.  For there are both gentleness and savagery, mildness and harshness, courage and timidity, fear and confidence, spiritedness and trickery, and, with respect to intelligence [dianoia], something like judgment [sunesis], similar in many ways. . . . For some of these qualities differ only more or less with reference to human beings. . . . For nature passes little by little from the inanimate to animals, so that this continuity prevents one from seeing a border or perceiving on which side an intermediate form lies."

Aristotle argues that the moral psychology of wild animals is like that of children: they can have natural virtue and habitual virtue, but they cannot have the deliberative virtue that requires fully developed logos (Politics, 1332b1; Nicomachean Ethics, 1144b1-1145a5).  They can have the natural virtue that comes from being born with a good natural temperament that inclines them to do the right actions.  And they can have the habitual virtue that comes from obeying social rules so that they habitually do the right actions.

Only human adults are capable of deliberative virtue, which requires logos. And logos is the capacity for grasping explanatory accounts--for understanding both theoretical and practical syllogisms (Moss 2014).  In ethics and politics, explanatory accounts do not just prescribe right actions, they also explain why these are right.  Children and animals can be trained to know what they ought to do but without understanding why they ought to do it.  Virtue in the strict sense requires deliberate choice and prudential judgment with full knowledge of both what should be done and why it should be done.  This deliberative virtue with prudence corresponds to what de Waal identifies as the third level of morality--reasoning and judgment.

Because of their unique capacity for logos, human beings are more political than the other political animals--and more moral than the other moral animals--because this capacity for grasping explanatory accounts means that rather than just habitually obeying social rules of justice in their group, human beings will want to know why these are the rules, and they will argue over whether there might be better rules.  For that reason, human politics is always a rhetorical activity in which people have to persuade one another that what their community is doing is just, right, or noble.  That's why Aristotle's Rhetoric is a crucial text for his moral and political philosophy.

The importance of rhetorical speech for human politics and human morality explains why language is the critical marker in the evolutionary transition to uniquely human symbolism and rationality, as Ginsburg and Jablonka have indicated.

ADDENDUM--SEPTEMBER 3, 2025

Abbate's article has been recently reprinted in a book edited by Andrew Linzey and Clair Linzey--Animal History: History as If Animals Mattered (Eugene, Oregon: Resource Publications, 2025).  In this new version of her paper, she makes no attempt to answer my objections.  Is that because my objections are irrefutable?

REFERENCES

Abatte, Cheryl E. 2016. "'Higher' and 'Lower' Political Animals: A Critical Analysis of Aristotle's Account of the Political Animal." Journal of Animal Ethics 6:54-66.

Abatte, Cheryl E. 2018. "Redefending Nonhuman Justice in Complex Animal Communities: A Response to Jacobs."  Journal of Animal Ethics 8:159-165.

Arnhart, Larry. 1990. "Aristotle, Chimpanzees, and Other Political Animals." Social Science Information 29:479-559.

Arnhart, Larry. 1994. "The Darwinian Biology of Aristotle's Political Animals."  American Journal of Political Science 38:464-485.

Arnhart, Larry. 1998. Darwinian Natural Right: The Biological Ethics of Human Nature. Albany, NY: State University of New York Press.

Arnhart, Larry. 2009. Darwinian Conservatism: A Disputed Question.  Ed. Kenneth Blanchard. Exeter, UK: Imprint Academic Press.

Bekoff, Marc. 1995. "Play Signals as Punctuation: The Structure of Social Play in Canids." Behaviour 132:419-429.

Bekoff, Marc, and Jessica Pierce. 2009. Wild Justice: The Moral Lives of Animals. Chicago: University of Chicago Press.

Darwin, Charles. 2004. The Descent of Man.  Second edition. Ed. James Moore and Adrian Desmond. London: Penguin Classics.

de Waal, Frans. 2006. Primates and Philosophers: How Morality Evolved. Princeton, NJ: Princeton University Press

Ginsburg, Simona, and Eva Jablonka. 2019. The Evolution of the Sensitive Soul: Learning and the Origins of Consciousness.  Cambridge, MA: MIT Press.

Jacobs, Edward. 2018. "Aristotle and the Zoon Politikon: A Response to Abbate." Journal of Animal Ethics 8:150-158.

Moss, Jessica. 2014. "Right Reason in Plato and Aristotle: On the Meaning of Logos." Phronesis 59:181-230.

Pierce, Jessica, and Marc Bekoff. 2012. "Wild Justice Redux: What We Know About Social Justice in Animals and Why It Matters." Social Justice Research 25:122-139.

Darwinism and the Catholic Church

In 1633, the Catholic Inquisition condemned Galileo as a heretic for endorsing the Copernican heliocentric theory of the Earth as moving around the Sun, because this seemed to deny those Biblical passages that spoke of the fixity of the Earth. Galileo was sentenced to house arrest, and his book Dialogue Concerning the Two Chief World Systems was put on the Church's Index of Prohibited Books.

By contrast, Darwin's theory of evolution has never been officially condemned by the Vatican, and his books were never been put on the Index, although a book by his grandfather Erasmus Darwin was put on the Index.

The Catholic Church's condemnation of Galileo has often been cited by those who argue that there must be perpetual warfare between Biblical religion and modern science. But the Church's handling of the debate over Darwinian evolution shows that the Church's hierarchy learned a lesson from the Galileo affair--that it was a big mistake to interpret the Bible as contradicting modern science.

By the middle of the twentieth century, Pope Pius XII praised Galileo as an intellectual hero and declared in his 1950 encyclical Humani Generis that there was no necessary conflict between Biblical faith and the theory of evolution. Pope John Paul II apologized for the condemnation of Galileo, and in 1996 he declared that the Church did not oppose Darwin's theory. A few years ago, I wrote a short essay on John Paul's statement.

We now have more information about the history of the Vatican's deliberations about evolution. In 1998, Cardinal Joseph Ratzinger (now Pope Benedict XVI) authorized the opening of the Archive of the Congregation for the Doctrine of the Faith in the Vatican. This congregation was originally called the Holy Roman Inquisition, which goes back to the beginnings of the Inquisition in 1231. This Archive includes the records of the Vatican's handling of the evolution debate at the end of the nineteenth century.

This archival material has become the basis for a book--Mariano Artigas, Thomas Glick, and Rafael Martinez, Negotiating Darwin: The Vatican Confronts Evolution, 1877-1902 (Johns Hopkins University Press, 2006). The book studies the cases of six Catholic authors who argued for the compatibility of evolution and Christianity. Of these, the most fascinating case, I think, is that of John Zahm, an American priest at the University of Notre Dame who provoked controversy with his book Evolution and Dogma (1896), which defended theistic evolutionism. The case of Zahm was complicated by the fact that he was identified as a proponent of "Americanism"--a movement among American Catholics to celebrate the moral and political principles of American life (such as the separation of Church and State) as a guide for Catholics.

Zahm defends the theory of evolution as superior to the theory of special creation. God did not have to miraculously create each form of life, because He could employ the "secondary causes" of evolution to carry out His creative purposes. Against the view of many Catholic theologians that God had to miraculously create the body of the first man, Zahm suggests that the human body could have originally evolved naturally from primate ancestors. But then the human soul had to be created immediately by God. To defend his position, Zahm had to argue that the Bible should not be read literally as a text of science, and that the distinction between God as Primal cause and nature's secondary causes allowed natural evolution as a creative process.

The newly available archival material shows that while Zahm's book was condemned by Church authorities, this condemnation was not published or officially sanctioned by the Holy See, and his book was not listed in the Index.

What one sees in this and the other cases is that the Vatican was cautious in not wanting to publicly condemn evolution for fear of falling into something like the Galileo affair.

Pope John Paul II's statement in 1996 shows how far the Church has moved towards accepting Darwinian evolution. In effect, as I argue in my essay on the Pope's message, he adopted St. George Jackson Mivart's position that while the human body and all other forms of life might be products of Darwinian mechanisms, the human soul must have been created directly by a miraculous intervention of God into nature.

As I indicate in my essay, the next good step for the Vatican would be to recognize that even the human soul could have arisen by 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 indicated in a recent article in Scientific American, comparisons of the genomes of humans and chimpanzees suggests that the uniqueness of human beings could have arisen from some uniquely human DNA sequences that regulate the development of the human cerebral cortex and neural mechanisms that control the human capacity for speech.

If our being created in God's image is manifested in our uniquely human capacities for reason and speech, the emergent evolution of the brain to support those capacities could explain the natural basis for that creative activity.

If Humans and Chimps Are 15 Percent Genetically Different, What Difference Does That Make?

Think about how often you've heard it said that the genetic difference between human beings and chimpanzees is only slightly more than 1 percent, and therefore humans are 99 percent similar to chimps.  It is also said that this proves that chimps--and also bonobos--are our closest living evolutionary relatives.  This seems to be confirmed by the fact that chimpanzees and bonobos are more genetically similar to humans than to gorillas.  This 1 percent difference between humans and chimps fits the evolutionary timeline of five to eight million years since humans and chimps diverged from their last common ancestor.

But now an article published last May in Nature (Yoo et al., 2025) reports that a complete sequencing of ape genomes shows that the genetic difference between humans and chimps is a lot greater than 1 percent--more like 15 percent!  And yet perhaps I shouldn't say this article "reports" this because if you read the main article, you won't see this claim of a 15 percent difference.  You have to go to the Nature website and print out the "Supplementary Data" for the article, and even then, you have to work through the technical jargon to find the 15 percent difference.  Casey Luskin has posted a helpful article at the Discovery Institute website that digs deep into the "Supplementary Data" to uncover this remarkable finding.  You would think that such a surprising discovery would be prominently announced in Nature and in press releases: "The Chimp-Human Genetic Difference Is Not 1% But 15%!"  I think Luskin is right to suggest that the editors at Nature must have worked hard to hide this finding because it refutes the popular claim about "only a 1% difference" separating humans and chimps.  

Luskin says this refutes one of the "icons of evolution," as Jonathan Wells called them--that is, widely believed assertions about evolution that the proponents of "intelligent design theory" and "young-Earth creationism" deny.  It's not surprising, therefore, that creationists like Ken Ham have cited Luskin's article as proving that the creationists are right to deny that there is any common evolutionary ancestry linking humans and apes.  Ham explains that Bible teaches us that God created the "ape kind" and the "humankind" separately and created humans as a unique kind made in the image of God.

And yet I don't see that this newly discovered "15% difference" provides any support for the intelligent design theorists or the creationists in their denial of evolutionary science.

But first we need to understand how this new research allows us to calculate genetic difference and similarity.  The title of the article in Nature is "Complete Sequency of Ape Genomes."  The emphasis is on "complete," because the first human and ape genome sequences were incomplete.  They excluded extremely repetitive sequences and large-scale structural differences such as inversions and duplications of genomic sequences.  So the first reports of only 1% differences between human and chimp genomes were based on incomplete drafts of the genomes.  But now the complete sequency in this article allows for a fuller comparison of similarities and differences in the sequences.

The authors found two kinds of differences--"gap divergence" and "single nucleotide variation" (SNV).

Luskin prepared this figure to illustrate the difference between "SNVs" and "Gaps" between two genomes.  Gaps represent nucleotides or segments of nucleotides that don't exist in one of the genomes.  SNVs represent places where the nucleotides are different for the two genomes.  In this illustration, we have 30 nucleotides of the target genome with 3 SNVs and 9 gaps relative to the query genome.  So SNV divergence is 10%, and gap divergence is 30%, which means a total divergence of 40%.

If you go to the Supplemental Data for the Yoo et al. article, you will see that Figure III.12 shows the SNVs in comparing the genomes for humans, chimpanzees, bonobos, and orangutans--the four "great ape" species who belong to the Hominidae family.  When the human genome is the "target" genome, the "gap divergence" for the gorilla genome is 27.3 percent, for the Sumatran orangutan it's 16.5 percent, for the bonobo it's 14.4 percent, and for the chimpanzee it's 13.3 percent. 

Figure III.11 shows the SNV divergences, which are 2 percent for the gorilla, 3.6 percent for the Sumatran orangutan, 1.6 percent for the bonobo, and 1.6 percent for the chimpanzee.

If we add the gap divergences to the SNV differences, we get these total degrees of difference between human and ape genomes: 29.3 percent for the gorilla, 20.1 percent for the Sumatran orangutan, 16 percent for the bonobo, and 14.9 percent for the chimpanzee.  That's how we get the estimate of almost 15 percent difference between the chimp and human genomes, which is a lot higher than the purported 1 percent difference.  

It should be noted that these comparisons are for the 44 non-sex chromosomes in the human genome--that is, excluding the X and Y chromosomes.  As compared with chimps, the human X chromosome has a 4.4 percent gap divergence and 1.1 percent SNV divergence, while the human Y chromosome has an amazing 56.6 percent gap divergence and 3.9 percent SNV divergence.

Although this new research shows that the genetic differences between humans and apes are greater than had been previously reported, this does not deny the evolutionary story of the common evolutionary ancestry of humans and apes.  The genetic similarity between humans and apes is still very great--85 percent!  And humans are more genetically similar to chimps and bonobos than they are to orangutans and gorillas, which supports the claim that chimps and bonobos really are our closest living evolutionary relatives.

ALL IN THE GENES?  OR FOUR DIMENSIONS OF EVOLUTION?

There is an obvious problem here, however.  All of us have seen chimpanzees in zoos.  And many of us have seen bonobos if we have gone to zoos in San Diego, Milwaukee, or Cincinnati that have bonobos.  Those zoos often have displays that say something about the 1 percent difference between humans and chimpanzees.  Now those displays might have to be changed to read 15 percent.  But even so, when we look at those apes and compare them with humans, it's very hard to believe that the difference is only 1 to 15 percent.  It's simply not true that humans and apes are 85 percent the same.  The gap between the mental achievements of human beings and those of the apes is staggering.

Most human beings don't believe that evolutionary genetics can fully explain that gap, and that's why so many people reject the science of evolution, and why so many believe that the superiority of the human mind over the ape mind can only be explained by the supernatural work of an Intelligent Designer or Divine Creator.

They are right to believe that evolutionary genetics cannot fully explain the achievements of the human mind.  But that's because genetics is only a small part of evolutionary science.  As I have indicated in some previous posts, there are four levels of evolutionary inheritance--genetics, epigenetics, culture, and symbolism (Jablonka and Lamb, 2005).

The genetic inheritance system is the foundation for the Neo-Darwinian theory of evolution. But genetic reductionism and determinism fail to see how gene action depends on the complexity of interacting causes within the genome, within cells, within organisms, within groups of organisms, and within ecological circumstances. Except for a few single-gene genetic disorders, "genetic astrology"--the idea that genes directly control specific traits--must be dismissed as foolish.

The epigenetic inheritance system is evident in the differences between specialized cells. Brain cells, liver cells, and skin cells are very different, although the nucleus of each cell has the same genome. Their differences are epigenetic, rather than genetic, because they have arisen through their developmental history in which there were different patterns of gene activation and interaction within the cell. This developmental information is passed on as these cells divide to produce more cells of the same kind. It is possible for evolution to occur through heritable epigenetic variation even without genetic variation. Just as a musical recording transmits interpretations in musical performances of a musical score, so does an epigenetic inheritance system transmit interpretations of the information in DNA, so that there is a Lamarkian inheritance of phenotypes instead of genotypes. One version of such inheritance that is now under active study is DNA methylation: strands of DNA are chemically modified during development, and these modifications can be transmitted through reproduction.  The chemical modification in epimutation is not in the DNA itself but in the chromatin marking. Methylated DNA has a small methyl group attached to some of its bases. The pattern of methylation influences which regions of DNA are expressed. The different kinds of cells in the human body have the same DNA, but the different patterns of methylation regulate the expression of DNA.

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. 

To explain why humans are somewhat similar to the great apes and yet radically different from them, we have understand how all four levels of human evolution have shaped human beings to be the unique animals that they are.

COMMON DESCENT OR INTELLIGENT DESIGN?  OR BOTH?

Although Casey Luskin is an advocate of intelligent design theory as the best alternative to evolutionary science, he stresses that he is not pointing to the new estimate of 15 percent difference between humans and chimps as evidence that refutes evolution.  As long as the five to eight million years since humans and chimps diverged from their last common ancestor is enough time for this 15 percent difference to evolve, then the evolutionary story of common ancestry is still defensible.  

But still, Luskin suggests, intelligent design theory has a better explanation for this genetic similarity--85 percent--between chimps and humans:  "Functional genetic similarities between humans and chimps could be explained by common ancestry or by common design.  Common ancestry is not the only way to explain genetic similarities.  Intelligent agents can re-use functional code in different designs.  Common design can explain shared functional genetic similarities just as well as common descent can."

There are two mistakes in Luskin's reasoning, however.  First, he mistakenly assumes a dichotomy between common descent and common design, as if they were mutually exclusive.  As I have noted previously, one of the leading advocates of intelligent design theory--Michael Behe--argues (in The Edge of Evolution) that the genetic similarity between humans and chimps is evidence that human beings evolved from primate ancestors shared with chimpanzees.  He explains that intelligent design is required to explain the emergence of the higher taxonomic levels of life (kingdoms, phyla, classes) but not the lower levels (orders, families, genera, species).  This means that the evolution of species could be fully Darwinian.

Behe is an intelligent-design evolutionist, because he insists: "The possibility of intelligent design is quite compatible with common descent, which some religious people disdain.  What's more, although some religious thinkers envision active, continuing intervention in nature, intelligent design is quite compatible with the view that the universe operates by unbroken natural law, with the design of life perhaps packed into its initial set-up" (166).  Luskin refuses to recognize Behe's position.

Luskin is also mistaken, however, in assuming the plausibility of the arguments for intelligent design.  He thus ignores my objection that the arguments for intelligent design are fallacious in two respects.  First, intelligent design reasoning depends completely on the fallacy of negative argumentation from ignorance, in which intelligent design proponents argue that if evolutionary scientists cannot fully explain the step-by-step evolutionary process by which complex living forms arise, then this proves that these complex forms of life must be caused by the intelligent designer.  This is purely negative reasoning because the proponents of intelligent design can offer no positive explanation of their own as to exactly when, where, and how the intelligent designer caused these forms of life.  

The second fallacy is the subtle use of the fallacy of equivocation--in the equivocation between human intelligent design and supernatural intelligent design.  We have all had the experience of seeing how human intelligent agents create artificial products by intelligent design.  But it does not follow logically from this that we have all had the experience of seeing how supernatural intelligent agents create artificial products by intelligent design.

CREATED BY GOD IN HIS IMAGE?  OR EVOLVED IN THE IMAGE OF PRIMATES?  OR BOTH?

Ken Ham (2025) argues, on the contrary, that even if we have not seen with our own eyes God creating everything out of nothing, this has been revealed to us through the Bible; and part of that revelation is that God created all the "kinds" of plants and animals separately, and He created the "chimp kind" to be utterly different from the "humankind," which was created in His image.

But as I have said in my previous posts on Ham and his two museums in Kentucky--the Creation Museum and the Ark Encounter--he mistakenly assumes that he is conveying the clear meaning of the Bible and that the Bible's clear teaching is incompatible with Darwinian evolution.

The Bible says nothing about God creating apes and humans as separate "kinds."  The Book of Genesis never mentions apes.  Actually, in the whole Bible, the Hebrew word for "ape" appears only twice (I Kings 10:22, 2 Chronicles 9:21), and never in the context of creation.  And while Genesis speaks of God creating plants and animals "after their kind," it never identifies human beings as a "kind."  Consider Genesis 1:26--"And God said, Let us make man in our image, after our likeness."  The phrase "after our likeness" takes the place of "after their kind," suggesting that in being created in the likeness of God, man is not bound by a "kind."  So there is no Biblical basis for Ham to speak of "humankind."

Moreover, the Hebrew word min that is translated as kind in the King James Bible is ambiguous.  In the Latin translation of the Bible, min is translated as the Latin word species.  Consequently, for almost two thousand years, Biblical believers assumed that God's creating "kinds" meant that God created each "species" separately, and that each species was eternally fixed.  But then after Darwin published his Origin of Species in 1859, in which he argued against the "theory of special creation" that God had created each species separating, some Christians began to believe that the created "kinds" in the Bible referred not to "species" but to some higher level of taxonomy.  Then, in 1941, the Christian biologist Frank Marsh coined the word baramin (combining the Hebrew words for "created" and "kind") as the best term for "created kind."  He argued that a "created kind" was not at the taxonomic level of "species" but at or near the level of "family."  This allowed Biblical believers to accept Darwin's theory of the origin of "species" by natural selection while also believing that God had created the "families" of plants and animals to be fixed and separate.  So, for example, we could say that God originally created the "family" of the finches, but within the limits of that "family," the separate species of finches endemic to the Galapagos Islands evolved by natural selection to be adaptive to those islands.

Notice what this means for the taxonomic classification of human beings.  If the "kind" of human beings refers to their taxonomic "family," then in modern taxonomy, human beings belong to the "family" of Hominidae, which includes chimps, bonobos, gorillas, and orangutan.  Even the young-earth creationist Todd Wood (2010) accepts this Hominidae classification of humans with the great apes, although he identifies the "human holobaramin" as the genus Homo.

This idea of "created kinds" was crucial for Ham in solving an old problem with Noah's Ark.  If the Ark carried all the "kinds" of land-based plants and animals, how could the Ark be big enough to hold all of the land-based species--which could be numbered in the millions?

Ham's creationist researchers have solved this problem by calculating that among these land-dependent vertebrate species, there are fewer than 1,400 known living and extinct kinds (that is, families).  This allows them to estimate that Noah had to have fewer than 6,744 individual animals on the Ark.  Once these animals left the Ark, speciation by natural selection within kinds could create all the living and extinct species that we know today.  The Ham's Ark Encounter is designed to show how as many as 6,744 animals and 8 human beings (Noah and his extended family) could survive on the Ark for almost a year.  But notice that this is a speculative reading of the Bible that never defines "kind" in this way.  This is not the clear meaning of the Bible, as Ham claims.  Indeed, if you go to the Ark Encounter in Kentucky, you might notice one display that speaks of the need for "Arktistic license" in making up details in the story of the Ark that have no basis in the Bible.

Since the Bible is so obscure in its creation story, and since so much of that story sounds like a figurative folk tale that was not meant to be a literal account of natural history, many Christians (like C. S. Lewis, Francis Collins, and Deborah Haarsma) have decided that the Bible could be read as allowing for theistic evolution or evolutionary creation.  According to this conception, God created the universal laws of nature at the beginning of the Universe, but then He allowed all the forms of life to emerge by natural evolution.  God is the "primary cause" of everything.  But the evolutionary process unfolds through the "secondary causes" of nature.  Even Darwin himself accepted this metaphysical conception of "dual causality" that reconciles belief in God as First Cause with acceptance of evolutionary science.  At various points in the Creation Museum and the Ark Encounter, there are displays that acknowledge that many if not most Christians accept some version of this theistic evolution.

But what about the creation of human beings in the image of God?  If the "image of God" refers to the God-like intellect of man, then we might argue that the extraordinary mental capacities of human beings could have evolved through the evolution of the primate brain.  I have argued that the evolution in the size and complexity of the primate brain passed over a critical threshold so that now there are 86 billion neurons in the human brain, and of that total, 16 billion are in the cerebral cortex, which includes 1.3 billion neurons in the prefrontal cortex.  That emergent evolution of the brain created the uniquely powerful human mind.  We were created in the image of the primate brain.

Even if we are only 15 percent genetically different from chimps, we are different in kind from chimps because we have the mental capacities for language, morality, and symbolic abstraction that they do not have at all.  That's the difference that makes all the difference.

REFERENCES

Behe, Michael. 2007. The Edge of Evolution: The Search for the  Limits of Darwinism. New York: The Free Press.

Ham, Ken. 2025. "Study Finds Chimp DNA Is Not '99% Identical' to Ours." Answers in Genesis. Ken Ham Blog. May 27. Online.

Jablonka, Eva, and Marion J. Lamb. 2014. Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life. Revised edition. Cambridge: MIT Press.

Luskin, Casey. 2025. "Fact Check: New 'Complete' Chimp Genome Shows 14.9 Percent Difference from Human Genome." Science and Culture Today, May 21, online.

Wood, Todd Charles. 2010. "Baraminological Analysis Places Homo habilis, Homo rudolfensis, and Australopithecus sediba in the Human Holobaramin." Answers Research Journal 3: 71-90.

Yoo, Dong Ahn, et al. 2025. "Complete Sequencing of Ape Genomes." Nature 641: 401-418.