Was the panda’s “thumb” designed? (Part one)

In a recent journal article titled, God, Gould, and the Panda’s Thumb (Religions 2023, 14(8), 1006; https://doi.org/10.3390/rel14081006), former philosophy professor Stephen Dilley, who is currently a Senior Fellow with Discovery Institute’s Center for Science and Culture, takes aim at an influential argument for evolution formulated by the late paleontologist Stephen Jay Gould (1941-2002) in his best-selling book, The Panda’s Thumb (Norton and Company: New York and London, 1980). Sadly, Professor Dilley manages to completely misconstrue Gould’s argument, which isn’t about God at all, but about engineering. This can be shown by the fact that even if we delete the two brief references to God and the single reference to an omnipotent creator and replace them with “an engineer,” and if we replace the reference to God’s “wisdom and power” with the term “skill,” then Gould’s argument still makes perfect sense. I maintain that Gould’s use of theological terms is a mere embellishment which obscures the central point he is making: namely, that mere tinkering (i.e. a series of step-by-step natural changes involving the adaptation of pre-existing parts) does not warrant an inference to intelligent design, as it requires no foresight. The panda’s “thumb” works very well, but it appears to be the product of tinkering and shows no signs of foresight on the part of whatever produced it, in the way it is put together. Instead, it is best described as a “contraption,” adapted from “a limited set of available components” via a series of natural transformations, which “follows automatically from simple hypertrophy [i.e. a massive increase in size] of the [panda’s] sesamoid bone.”

Engineers, who design things intelligently, differ from Nature in three important ways regarding the manner in which they produce complex structures. First, they are not bound to use pre-existing parts when making things, as they can fashion their own if they so choose. Second, when using parts, they are in no way limited by the prior history of those parts. Finally, because they possess foresight, engineers are capable of making great conceptual leaps, allowing them to explore radical solutions which a series of step-by-step natural transformations might never be able to reach. These features are strikingly absent when we examine the panda’s “thumb.”

Gould’s argument reconstructed

The panda’s “thumb,” which is actually a radial sesamoid bone, is shown in red. Image courtesy of Wikipedia.

Here is what I see as the core of Gould’s argument, excerpted from his book, The Panda’s Thumb (1980, pp. 20-24). The tiny changes I have made are highlighted in red. I have also omitted the word “divine” in the final quote from Francois Jacob, as Gould’s argument does not require it.

Gould begins his argument with a discussion of orchids, which attract insects using an impressive array of techniques that might lead a naive observer to conclude that they were designed. Closer examination reveals that this is not the case, as these techniques for attracting insects all suffer from a common limitation:

Orchids manufacture their intricate devices from the common components of ordinary flowers, parts usually fitted for very different functions. If an engineer had designed a beautiful machine to reflect his skill, surely he would not have used a collection of parts generally fashioned for other purposes. Orchids were not made by an ideal engineer; they are jury-rigged from a limited set of available components. Thus, they must have evolved from ordinary flowers…

[I]deal design is a lousy argument for evolution, for it mimics the postulated action of an engineer. Odd arrangements and funny solutions are the proof of evolution — paths that a sensible engineer would never tread but that a natural process, constrained by history, follows perforce… Which brings me to the giant panda and its “thumb.”

The panda’s “thumb” is not, anatomically, a finger at all. It is constructed from a bone called the radial sesamoid, normally a small component of the wrist. In pandas, the radial sesamoid is greatly enlarged and elongated until it almost equals the metapodial bones of the true digits in length. The radial sesamoid underlies a pad on the panda’s forepaw; the five digits form the framework of another pad, the palmar. A shallow furrow separates the two pads and serves as a channel way for bamboo stalks.

The panda’s thumb comes equipped not only with a bone to give it strength but also with muscles to sustain its agility. These muscles, like the radial sesamoid bone itself, did not arise de novo. Like the parts of Darwin’s orchids, they are familiar bits of anatomy remodeled for a new function... The abductor of the radial sesamoid (the muscle that pulls it away from the true digits) bears the formidable name … “the long abductor of the thumb”… In other carnivores, this muscle attaches to the first digit, or true thumb. Two shorter muscles run between the radial sesamoid and the pollex [Latin for “thumb”]. They pull the sesamoid “thumb” towards the true digits…

In most carnivores, the same muscles that move the radial sesamoid in pandas attach exclusively to the base of the pollex, or true thumb. But in ordinary bears, the long abductor muscle ends in two tendons: one inserts into the base of the thumb as in most carnivores, but the other attaches to the radial sesamoid. The two shorter muscles also attach, in part, to the radial sesamoid in bears. “Thus,” Davis concludes, “the musculature for operating this remarkable new mechanism — functionally a new digit — required no intrinsic change from conditions already present in the panda’s closest relatives, the bears. Furthermore, it appears that the whole sequence of events in the musculature follows automatically from simple hypertrophy of the sesamoid bone.

The sesamoid thumb of pandas is a complex structure formed by marked enlargement of a bone and an extensive rearrangement of musculature. Yet Davis argues that the entire apparatus arose as a mechanical response to growth of the radial sesamoid itself. Muscles shifted because the enlarged bone blocked them short of their original sites…

The panda’s thumb provides an elegant zoological counterpart to Darwin’s orchids. An engineer’s best solution is debarred by history. The panda’s true thumb is committed to another role, too specialized for a different function to become an opposable, manipulating digit. So the panda must use parts on hand and settle for an enlarged wrist bone and a somewhat clumsy, but quite workable, solution. The sesamoid thumb wins no prize in an engineer’s derby. It is, to use Michael Ghiselin’s phrase, a contraption, not a lovely contrivance. But it does its job and excites our imagination all the more because it builds on such improbable foundations…

Nature is, in biologist Francois Jacob’s words, an excellent tinkerer, not an … artificer.

The panda’s vindication

A giant panda feeding on bamboo. Image courtesy of Chen Wu and Wikipedia.

Gould’s argument can now be stated syllogistically:

1. A complex structure does not warrant the ascription of intelligent design if its origin can be accounted for by means of a series of step-by-step natural transformations involving the adaptation of pre-existing parts fitted for different functions. Such a structure is best described as a natural contraption, rather than an artificial contrivance.

2. The complex structures that we find in nature are typically structures whose origin can be accounted for in this fashion. Orchids and the panda’s thumb are two well-known instances drawn from the plant and animal kingdoms respectively.

3. Therefore the general inference we should draw is that the complex structures found in nature are contraptions, not contrivances, and that intelligent design was not required to produce them.

In reply, it might be pointed out that the foregoing syllogism doesn’t establish that all of the complex structures we find in Nature are contraptions. All it takes is a a single complex structure which couldn’t have arisen via the natural process described above, to warrant an inference to intelligent design. It might therefore be urged that so long as there are some complex structures which have not been shown to be mere contraptions, intelligent design remains a live option. Or does it?

In his day, Charles Darwin was at a loss explain the origin of the vertebrate eye, beyond noting that the eyes of some animals were much more rudimentary and speculating that a series of transformations from simple to complex eyes must have taken place in the distant past. Given his state of ignorance at the time, should Darwin have opted for a design-based explanation of the origin of the eye, instead? Not necessarily. He could have reasonably pointed to the foregoing syllogism and declared: “As we have seen, some of the most striking instances of alleged design in the natural world turn out to be natural contraptions. I can’t yet explain the origin of the eye in this way, but no-one has shown me any good reason to believe that it can’t be done. I will therefore continue with my endeavor to explain all observed complex structures in terms of naturalistic processes which do not require any foresight to produce their effects.”

In my next post, I’ll take a look at Professor Dilley’s recent articles on the panda’s “thumb” at Evolution News, as well as his more substantive article, God, Gould, and the Panda’s Thumb (Religions 2023, 14(8), 1006; https://doi.org/10.3390/rel14081006). Stay tuned!

14 thoughts on “Was the panda’s “thumb” designed? (Part one)

  1. Hi VJ
    If the Pandas thumb is the product of evolution then it must share ancestry with another bear. How many genetic changes do you need to become fixed in a population to modify an ancestral bear thumb? Can a population genetics model account for this?

    Most bear species have 36 autosomes and two sex chromosomes, except for the giant panda (20 autosomes and two sex chromosomes) and the Andean bear (25 autosomes and two sex chromosomes).

    Is there a population genetics model that can account for this reduction in chromosome counts given chromosome fusions are highly deleterious?

  2. I guess I’m out of date, sort of.

    For many decades, the precise taxonomic classification of the giant panda was under debate because it shares characteristics with both bears and raccoons.[3] However in 1985, molecular studies indicate the giant panda is a true bear, part of the family Ursidae.[4][5] These studies show it diverged about 19 million years ago from the common ancestor of the Ursidae;[6] it is the most basal member of this family and equidistant from all other extant bear species.[6][7] The giant panda has been referred to as a living fossil


  3. Hi colewd,

    Sorry for not getting back to you sooner. Regarding chromosome number in the ancestral bear, it seems that experts were divided on the subject in the late 1990s, with some opting for 42 (the same number as in the panda, and also in the original ancestral carnivore) and others opting for 74 (the same number as in most bears today).

    More recently, W. Nie et al. have published a paper titled, Chromosomal rearrangements and karyotype evolution in carnivores revealed by chromosome painting (Heredity volume 108, pages17–27 (2012)). If you scroll down to Figure 7, you can see what they’re proposing. The original ancestral carnivore had 42 chromosomes (2n=42). In the line leading to bears, there were then 16 fission events, leading to 32 extra chromosomes and a total of 74 (as in most bears today). There was also an inversion on chromosome #19. Then, after that, on the line leading to giant pandas, there were 16 fusions (bringing the total back to 42) and another inversion (on chromosome 3). On the line leading to other bears, there were two fission events (increasing the chromosome count to 78), and in the line leading to spectacle bears, 11 fusions and one inversion, bringing the chromosome count back to 52. In the line leading to other bears, there were instead two fusions, bringing the chromosome count from 78 back to 74. Sounds pretty complicated, but that’s what they’re arguing, and they have lots of pictures of matching chromosomes in different carnivores to back up their case.

    You wrote that chromosomal fusions are highly deleterious. Could you supply a reference, please? After all, there’s one in the human line: chimps and gorillas (our nearest relatives) have 48 chromosomes, while humans have 46. One paper I’ve looked at says: “Chromosomal fusions may often have deleterious effects because fusions can lead to the loss of genetic material, alter gene expression, or increase the rate of segregation errors.” But there’s a big difference between “may” and “must.” Cheers.

  4. Hi colewd,

    You asked how many genetic changes were required for the panda’s thumb. Here’s an article that may help answer your question. It appears that changes in as few as two genes may have been sufficient.

    How the Panda’s “Thumb” Evolved Twice

    Strengthens the case for panda evolution, doesn’t it?

  5. In reply, it might be pointed out that the foregoing syllogism doesn’t establish that all of the complex structures we find in Nature are contraptions. All it takes is a a single complex structure which couldn’t have arisen via the natural process described above, to warrant an inference to intelligent design. It might therefore be urged that so long as there are some complex structures which have not been shown to be mere contraptions, intelligent design remains a live option.

    I think this is a logical fallacy anyway, because it rests on the presumption that we are justified in attributing magical explanations for anything not known or understood. Specifically, this states that we can positively identify a complex structure which could not have arisen naturally, which (by implication) we can distinguish from an equally complex structure whose history we cannot reconstruct.

    This is, of course, a simple example of how things not understood have been attributed to gods across time and across cultures. It’s a fairly recent development, since the advent of science, that many people have come to believe that things not understood nonetheless DO have a nonmagical basis, so the attribution to gods has shrunk to the (somewhat) narrower fields of biological origin, coincidence, and psychological projection or (mis)directed interpretation. Oh, and the ever-popular conspiracy theories.

  6. Flint: …it rests on the presumption that we are justified in attributing magical explanations for anything not known or understood. Specifically, this states that we can positively identify a complex structure which could not have arisen naturally, which (by implication) we can distinguish from an equally complex structure whose history we cannot reconstruct.

    It is equally contentious (and pretentious) to presuppose that magical explanations cannot be presupposed. Inevitably, something is always presupposed.

    ID theory fails because it assumes that one can specifically detect by calculations that such-and-such was designed and something else was not. The theory fails not because of magical background presuppositions, but because of the assumption that there is a hard line between “designed by intelligent agent” versus “not designed”. There is no mathematical or physical basis for such calculations. And there is no philosophical or theological basis for it either. If nature is Creation, then everything is “designed by intelligent agent” i.e. Creator, except man-made things, which are designed by a different intelligent agent. So, in theological or philosophical terms, there are no undesigned things whatsoever, which is plain standard classical philosophy and theology. ID theorists were lying both to their atheist opponents and to their religious supporters, which is why ID theory deserved to die the sooner the better.

    The theory of evolution (not in argument with ID theory, but in itself) fails because it assumes that everything evolves from simpler parts by itself step by step. This, if anything, is the cringiest explanation by magic. As far as science is concerned, there is no such observation ever been made. Experimentally, there is always a further observation of background forces and circumstances specifically designed to enable the “evolution”.

    The assumption that everything “more complex” evolves by itself from “simpler” parts/entities is a philosophical theory called atomism. It is a philosophical school of thought, not strictly science. Many modern scientists are silently atomists, if they have any clue about philosophy at all. Mostly they don’t have any clue, and in their cluelessness they falsely assume that they are free from any presuppositions and background assumptions. Thus they are doomed to fail further until they hopefully get a clue.

  7. Biological evolution is not a theory that everything evolves or that things evolve by themselves.

  8. Hi colewd,

    You wrote:

    Here is a paper on chromosome fusion causing sterility. This is one of many.


    The sterility referred to in the paper is hybrid sterility. This, in and of itself, isn’t deleterious; it’s simply a reproductive isolating mechanism. Indeed, the paper itself acknowledges:

    Chromosome fusions are one of the major types of mutations shaping the evolution and divergence of genomes in different species, and meta-analyses of changes in chromosome numbers have suggested their importance in speciation in mammals, reptiles and butterflies1,2,3,4


    1. Bush, G. L., Case, S., Wilson, A. & Patton, J. Rapid speciation and chromosomal evolution in mammals. Proc. Natl Acad. Sci. USA 74, 3942–3946 (1977).

    2. Olmo, E. Rate of chromosome changes and speciation in reptiles. Genetica 125, 185–203 (2005).

    3. Leaché, A. D., Banbury, B. L., Linkem, C. W. & de Oca, A. N.-M. Phylogenomics of a rapid radiation: is chromosomal evolution linked to increased diversification in North American spiny lizards (genus Sceloporus)? BMC Evol. Biol. 16, 63 (2016).

    4. de Vos, J. M., Augustijnen, H., Bätscher, L. & Lucek, K. Speciation through chromosomal fusion and fission in Lepidoptera. Phil. Trans. R. Soc. Lond. B 375, 20190539 (2020).

    Chromosomal reduction is well-studied in the muntjac deer, where it has occurred extensively. See this paper:

    Wen Wang, Hong Lan, Rapid and Parallel Chromosomal Number Reductions in Muntjac Deer Inferred from Mitochondrial DNA Phylogeny. Molecular Biology and Evolution, Volume 17, Issue 9, September 2000, Pages 1326–1333, https://doi.org/10.1093/oxfordjournals.molbev.a026416.

    From the abstract:

    Muntjac deer (Muntiacinae, Cervidae) are of great interest in evolutionary studies because of their dramatic chromosome variations and recent discoveries of several new species. In this paper, we analyze the evolution of karyotypes of muntjac deer in the context of a phylogeny which is based on 1,844-bp mitochondrial DNA sequences of seven generally recognized species in the muntjac subfamily. The phylogenetic results support the hypothesis that karyotypic evolution in muntjac deer has proceeded via reduction in diploid number. However, the reduction in number is not always linear, i.e., not strictly following the order: 46→14/13→8/9→6/7… Analyses of sequence divergence reveal that the rate of change in chromosome number in muntjac deer is one of the fastest in vertebrates. Within the muntjac subfamily, the fastest evolutionary rate is found in the Fea’s lineage, in which two species with different karyotypes diverged in around 0.5 Myr.

  9. vjtorley,

    Hi VJ
    I the strict sense of the meaning of deleterious you are correct. I use it for mutations that are not advantageous or neutral.

    The problem is that population genetics cannot reconcile the differences…not even close given the frequency of mutations and how the differences generate isolation and inferior reproduction.

    The current model of Universal common descent is not only wrong it is leading to thousands of misguided papers that assume reproductive connection between species.

    I generated a post at peaceful science on the chromosome and gene differences between deer species.


  10. colewd: I generated a post at peaceful science on the chromosome and gene differences between deer species.

    Glad you owned up to it, Bill. 😉

  11. Alan Fox,

    Glad you owned up to it, Bill.

    I guess I never got the message that biological sciences included story telling. 🙂

  12. colewd:
    Alan Fox,

    I guess I never got the message that biological sciences included story telling. 🙂

    That’s what a hypothesis is, a narrative to explain some phenomenon. Then test the story against reality by observation and experiment.

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