Two weeks ago I wrote a four-part post analyzing the claims of Don McLeroy, former chairman of the Texas Board of Education, based mostly on an interview I did with him on the SGU. The posts also included some responses from Don. Don has been travelling, but has now returned and had time for a thorough response to the entire series of posts. Here is his response in its entirety, with my reply following:

Steven,

For me, the main topic under discussion is the strength and weakness of the evidence for evolution. My entire argument in 2009 and today is that the evidence supporting evolution—the idea that all life is descended from a common ancestor due to unguided natural processes—is weak.

Again, the key criterion for science is testability. Evolution is overwhelmingly tested historically by making observations—finding evidence. The more evidence found the stronger the case; the less evidence found the weaker the case.

I have read your comments and the comments of others posted on your podcast and NeuroLogica blog posts. Here is the summary of actual evidence that I gleaned from these comments. I probably missed some, but I do not think it invalidates my argument about the weakness of the evidence for evolution.

From The Skeptics Guide to the Universe Episode #408

• Marx Reply #35 states “Not sure about anyone else, but I found the most compelling evidence on evolution is just going outside & looking at animals & plants. It’s all kinda makes sense after a bit of that. “ At least he is on topic.
• trul Reply #114 states “While the fossil evidence for the evolution of the complexity of the cell may be forever weak, the genetic evidence just gets stronger and stronger. “ But no evidence is offered.

 

NeuroLogica: An Interview with Don McLeroy Part I 

Evidence from Steven Novella

• None

Evidence from others 

• Skeptical Steel states there is a “preponderance of evidence” but no evidence is offered.

 

NeuroLogica: An Interview with Don McLeroy Part II

Evidence from Steven Novella

• You seem to contradict yourself. You state “new body plans do not arise out of nowhere’” after stating that all phyla basically had a sudden “first appearance.”
• You state there is a pattern of nested hierarchies.  Why does this imply only evolution?
• You state that there are numerous transitional fossils—specifically Ambuloceus.  (Evidence #1)

Evidence from others

• Mapple offers “the recurrent laryngeal nerve.” (Evidence #2)
• Rick K offers a specific—the  “Lenski experiments, (Evidence #3)” then generalizes  “shared DNA, inherited ERV markers, molecular biology, vestigial traits, atavisms, genetic mutation, embryology, nested hierarchies in the fossil record, transitional species predictions, radiometric dating, dendrochronology, thermoluminescence dating, ice core dating, biostratiography, archaeogenetics, biogeography, and plate tectonics.”

 

NeuroLogica: An Interview with Don McLeroy Part III

 Evidence from Steven Novella

• None

Evidence from others   

• Enzo says it is absurd “Calling writers out for choosing examples rather than present the molecular evidence for every single signaling pathway in the cell?” I agree. I just expect SOME evidence.
•  LC states”we would EXPECT the fossil evidence for biochemical evolution to be scant to nonexistent…” It seems some commentators agree with me that the evidence is weak.
• Davdoodles states that the fact that cells exist are evidence that they evolved. “The fact is that these complex cells exist. Even in the absence of any other evidence (which is only an assumption for present purposes), it is not a difficulty for the theory of evolution, it is merely a scientific question awaiting a solution.”
• Rocken 1844 offers “long dead proteins.” (Evidence #4) While not specific, he does provide a link.

 

NeuroLogica: An Interview with Don McLeroy Part IV

Evidence from Steven Novella

• I do not argue that the evolutionists must do the impossible and provide detailed evidence for biochemical pathways; I only expect that they must provide at least SOME evidence—especially since “biochemical complexity must underlie morphological complexity.” (Jerry Coyne)
• You also seem to agree with me that the evidence is weak. You state:

o   “Evolution can be true even if we are currently unable to provide robust evidence for the evolution of biochemical pathways.” (Emphasis added.)

o   “We are therefore limited in our ability to reconstruct the evolutionary history of billions of years of evolution on this scale.” (Emphasis added.)

o   “Scientists only have a few methods available from which to infer the evolutionary history of cell structures and biochemical pathways. “(Emphasis added.)

o   “In short scientists are doing the best they can unraveling an extremely complex picture with the relatively little evidence available to them.” (Emphasis added.)

• To argue that “popular writing is by necessity superficial” is to disagree with Stephen J. Gould who in Wonderful Life stated “The concepts of science …can be presented without any compromise, without any simplification counting as distortion, in language accessible to all intelligent people.” ( p.16)
• You do provide a link on biochemical development in prokaryotes (Evidence #5) and mention Endosymbiosis (Evidence #6).

Evidence from others

• Ifvvh provides a link to “experimental directed evolution in bacteria.” (Evidence #7)
• Cbeck challenges me to provide what Jesus had for breakfast on his 17^th birthday.  I have no idea—hummus?  But note, we are not teaching “Jesus” in our science curriculum in Texas.

Conclusion:

Again, evolution must be tested historically by providing evidence. Continental drift is an excellent example of historical testability. The (1) obvious fit of the coastlines of Africa and South America with (2) similar corresponding geologic formations, (3) along with the eventual discovery of the Mid Atlantic Ridge and (4) sea-floor spreading make a convincing argument.

Likewise, evolution is tested historically; thus, evolutionists need to present convincing evidence. A fair question is “How much evidence is enough to demonstrate evolution?” If four observations conveyed in a single sentence demonstrate continental drift, how many observations in how many sentences are needed to demonstrate evolution? Continental drift is a basically a division of a single land mass; it can be demonstrated by the simple tearing apart of a piece of paper. To repeat myself, a simple eukaryote cell division—mitosis—involves not only the division but replication of billions of molecules, hundreds of cell organelles, etc. I know of no simple demonstration for mitosis; we would need billions of sheets of paper. And, this is for only a miniscule phenomenon of biology.

The evidentiary requirements to demonstrate evolution are immense, but I find only seven in this extensive discussion.  Even if I add another like “Tiktaalek” you only have eight.

I rest my case.

Many folks asked me questions during this discussion—including you. I do not mind dealing with them separately as single topics.  You pick and choose a topic and I will answer you the best I can.

Again, I am impressed with you, the tone of this discussion and how you have moderated it. Thank you for this opportunity to have this discussion.

Don

My response:

Don,

Thanks for taking the time to respond. I will first address your logic, then the state of the evidence for evolutionary theory.

The previous blog posts were not meant to review all the evidence for evolution. I was addressing the specific points you made during the interview – the implications of stasis and sudden change in the fossil record, and the complexity of the cell. If you now want to expand the scope of this discussion to a summary of the evidence for evolution itself, I am happy to do that.

You also asked for specific questions – I will include them at the end.

Regarding the use of popular literature. Stephen J Gould was making the point that a science popularizer should not and does not have to dumb down the science (and the quote you provide refers to the “concepts” of science, not the technical details). He was not making the case that a lay person can use popular writing as a substitute for a deep knowledge of the technical literature. Ironically, you are proving this point quite well in your response – you are grossly mischaracterizing the state of the evidence for evolution.

The main thrust of your point is that the amount of evidence for evolution is scant while life is highly complex, therefore overall the evidence for evolution is weak. This claim is both logically flawed and factually incorrect. Science is not just about counting the number of pieces of evidence.

Science is about coming up with plausible and testable hypotheses, ones that make predictions, and then testing those hypotheses against the evidence. What we can say about evolutionary theory is that it has very successfully made predictions about future evidence. Further, it does so better than any competing theory (including any scientific formulation of intelligent design or creation). Also, sometimes a single piece (or line) of evidence can be extremely compelling. At present evolution is the best theory we have and it has been highly successful as a research paradigm. You cannot boil this down to – how many pieces of evidence do we have.

You state: “You seem to contradict yourself. You state “new body plans do not arise out of nowhere’” after stating that all phyla basically had a sudden ‘first appearance.'”

If you have read Stephen J. Gould then you would know the answer to this. Disparity is maximal at the beginning of multicelluar life then decreased over evolutionary time. Evolutionary history progressively constrains the possible pathways that evolution can take. All of the basic body plans evolved during the Cambrian explosion, when multicellular life was just starting and was maximally unconstrained. Subsequent evolution then involved variations on these basic themes (body plans). Entirely new body plans do not keep popping up throughout evolutionary history, however.

The Evidence for Evolution

Before we talk about the evidence for “evolution” we need to define what we mean. There are various components to evolutionary theory, which are independent to some degree. The first is the simple fact that species derive from a process of evolutionary change – descent with modification, and therefore all life on Earth shares common descent. The second is natural selection as a mechanism for evolutionary change. The third is the specific history of life on Earth – what evolved from what and when, and with what tempo and patterns. I will focus here on common descent and the basic fact of evolution.

Biochemical Pathways

What I have acknowledged is that, of all the lines of evidence for evolution, reconstruction of specific biochemical pathways is the most scant, because there is nothing to fossilize (unless you count genes, but I will discuss genetic evidence separately). Even still, while the weakest, overall the evidence for evolution from biochemical pathways is very strong.

Don – your method of counting the pieces of evidence presented in the previous blog posts is flawed and misleading. First, you counted two links when I provided three (Biochemical Pathways in Procaryotes can be Traced Backwards through Evolution Time, evolution of eukaryotic pathways by endosymbiosiss of prokaryotes, and another paper, the main conclusion of which is that as biochemical pathways evolved, cells became less dependent on exogenous material and more independent).

But your bigger mistake was to count each link as one piece of evidence, when they were review articles, each containing many pieces of evidence. The article on prokaryotes refers to at least a dozen lines of evidence, the review article on eukaryotes reviewed ten published papers, and the third paper has 117 references. I linked to review articles because it’s the quickest way to summarize large bodies of evidence. If you follow all the references on those three review articles you will find about a hundred lines of evidence for the evolution of biochemical pathways.

Do you want more? I plugged in “biochemical evolution” into PubMed and was rewarded with 8,948 references. They are probably not all relevant, but I read the abstracts on a dozen random samples, and most are. If you want to wade through the first thousand or so references you will probably find additional relevant evidence for biochemical evolution. (Or you can just trust the opinion of experts who have read the thousands of references.)

The Fossil Record and Transitional Species

The overall pattern in the fossil record is one of change over geological time in a pattern that is compatible with evolution. The most salient feature here is one of nested hierarchies. You asked if evolution is the only theory with which this pattern is compatible, and the short answer is yes. No other theory (other than the common descent component of evolution) predicts this pattern. Of course, you can contrive countless theories that would produce this pattern (successive waves of genetic manipulation by an advanced alien race) but Occam’s razor nicely excises any such theories. So perhaps I should say that evolution is the most elegant explanation of this pattern in the fossil record.

If you disagree – then please state a plausible theory that also explains this pattern, then explain why it is a better explanation than evolution, and if possible what predictions would distinguish it from evolution.

You then count, from this current blog exchange, two examples of transitional species, Ambulocetus and Tiktaalik. While these are impressive fossils, they are by no means an exhaustive list of transitional fossils. In reality, all species are transitional (they have cousins and ancestors), but for the sake of argument let’s count species that represent connections between genuses or higher order groups. Also, keep in mind I am not going to have time to scour the literature and provide an exhaustive list myself. Let’s see how many I can come up with in about 10 minutes of searching (I will “cheat” and refer to previous articles I have written).

A. sediba is a fossil hominin, a clear transition between apes and humans. But – look at the current fossil hominin tree. I count 22 individual hominin species.

Archaeopteryx, feathered dinosaurs, and the evolution of birds is an absolute home run for common descent. Here is a list of fossil bird species, including the basal birds (dozens of species).

Whale evolution is not just about Ambulocetus (that’s just a fun example because it is a literal walking whale). There are several species demonstrating a nice progression from land to water.

The evolution of reptiles to mammals is fairly well documented.

Here is an article I wrote about turtle evolution and a new transitional specimen found.

Here is my discussion of Tiktaalik. And here’s another transitional fish from the same scientists, Holoptychius bergmanni. 

These are just my favorite examples. Here is a longer list from Wikipedia, which is also not exhaustive but contains dozens more of examples of transitional fossils between major groups. Here are some more examples from Talk Origins.

And don’t forget, all of the Cambrian fauna and flora are transitional species.

Don – there are literally thousands of transitional species in the fossil record. Not two.

Genetic Evidence

As strong as the fossil evidence is, the molecular evidence is stronger still, because we can calculate the odds of the patterns we see being what they are without evolution – they are absurdly small, essentially impossible.

Here is a great overview of this evidence. Essentially, when we look at the pattern of nucleic acids in specific genes, the pattern of amino acids in proteins, and the pattern of fossil genes or viral inclusions we see a nested hierarchy of relationships that generally match each other and morphological relationships (of course, not perfect, as the evidence is incomplete and evolutionary history is complex). No matter what gene or protein we look at, we see that humans are more closely related to chimps than other primates, to primates than other mammals, to mammals than other vertebrates, to vertebrates more than invertebrates, and to all animals more than plants.

There is only one scientific explanation for this pattern, repeated thousands of times with high specificity – common descent.

Other Evidence

I am running short on time, so I will simply list the other categories of evidence, which include developmental biology, dating from geology and physics, modern biology including morphology and vestigial structures, and evidence for evolutionary change in the laboratory, most famously the Lensky experiments.

Conclusion

There are literally dozens of lines of evidence with thousands of pieces of evidence pointing towards and validating evolution, and specifically common descent. I have tried to provide a quick summary here, but it is not exhaustive. An encyclopedia would be necessary to thoroughly document this evidence.

Don – I await your reply.