27. Creation: Evidence For and Against Evolution
Evolutionary theory did not emerge in a vacuum. At the time Charles Darwin was writing, there was already significant fossil evidence that the different species inhabiting Earth had been changing over the course of Earth’s history. For example, trilobites, a nearly alien-looking sea creature, appear in the fossil record around 500 million years ago (Myr) and disappear around 250 Myr ago. If the radiometric dating techniques we discussed in last week’s episode are valid, then this implies there is a period of 250 Myr where trilobites are a ubiquitous creature, then they disappear before the emergence of dinosaurs, which make their first appearance around 230 Myr ago, with some of the more famous species of dinosaurs (e.g., Tyrannosaurus Rex and Triceratops) appearing during the late Cretaceous period, about 65 Myr ago. (It turns out Michael Crichton should have named his fameous Sci-Fi novel Late Cretaceous Park, but I don’t think that has the same ring to it).
Example fossils which appear in different sedimentary layers with little to no overlap, suggesting some ancient species have gone extinct, and some new species may have appeared in their place.
In response to this basic evidence, Darwin and others around the same time, suggested that the significant change in the composition of life on Earth over time was due to the gradual changing and branching of one species into one or more new species, hence the name of his book: On the Origin of Species.
There are several key pieces of evidence that are typically presented as supporting evolutionary theory. For now, I’m going to present these in the sections below, and then we’ll return to consider the fact that science does not progress by finding “supporting evidence,” it progresses by testing theories and desperately searching for disproving evidence.
Evidence for
Vestigial Organs
Seemingly related fish living outside (top) and inside (bottom two) caves in Mexico. The cave-dwelling fish do not have functioning eyes.
Adapted from Sifuentes-Romero et al. (2023)
A number of species appear to have organs which do not serve any critical function. In an evolutionary framework, these are interpreted as representing organs which were once important to the species but which are no longer useful, after considerable evolution and adaptation to a new biological niche. These organs are given the term “vestigial organs,” as they are assumed to represent the vestiges of an ancient evolutionary ancestor.
As a first example, we can consider the case of blind cave fish. There are some blind cave-dwelling fish which in Mexico, which look very much like the non-blind fish which live just outside the caves. The key difference is that the fish outside the cave have fully functioning eyes, which the fish inside the cave do not have functioning eyes. Instead, they have “vestigial” eye-like organs. This is typically considered to be evidence that a subset of fish migrated into the caves and adapted to that environment using other sensory input (e.g., a super-cool organ system called the “lateral line”) to navigate and feed. The proposal is that after many generation of life in the dark caves where eyes did not offer any advantage to the fish, this sub-species eventually evolved to not have fully functioning eyes.
Skeleton of baleen whale with pelvic structure highlighted in red ellipse.
As another example, we can consider the apparent pelvic bones of whales. Whales represent an unusual case regardless of one’s stance on evolution. They are unusual because they meet all of the typical qualifications for being considered a mammal (breathing air with lungs not gills, giving birth to live young, feeding milk to those young, etc.) except that they live their entire life in the water! The evolutionary argument is that these creatures are so unusual because they represent the descendants of land mammals who eventually adapted to live in the water. This is in contrast to modern fish, which are assumed to have absolutely no land-dwelling creatures in their evolutionary past.
One of the arguments that this evolutionary history is correct is the presence of what appears to be vestigial pelvic bones in modern whale skeletons. The assumption is that those pelvic bones were once connected to strong, leg-like bones and used to support and propel the terrestrial ancestors of whales. Now that whales do not need hind-legs since they live in the water, they have evolved to not have hind legs, while the vestiges of their land-dwelling past remain in the form of their pelvic bones, which hover in their body, disconnected from any legs.
Transition Fossils
If Darwin’s basic premise that new species are evolved out of older, pre-existing species, then we should expect to find some intermediate species representing a transition from one species to the next. There is no perfect definition of what qualifies as a transition fossil, but paleontologists generally agree that a transition fossil is one which exhibits some characteristics from both of the two species which it supposedly connects. For example, one would expect to find fossils of a species representing a transition from predominantly sea-dwelling creatures (e.g., fish) to predominantly terrestrial creatures (e.g., lizards).
Darwin was well aware that the existence (or non-existence) of these “transition fossils” was critical evidence on deciding the question of whether an evolutionary theory was viable or not. He was also aware of the fact that there was a significant lack of such transitionary fossils at the time of his writing in 1859. In fact, Darwin included a whole chapter in On the Origin of Species attempting to address the “The Imperfection of the Geological Record.”
What about the fossils which have been unearthed since Darwin’s time? Do they help fill in the gaps which existed when he was alive? Before we look at that, it’s important to pause and examine what the fossil evidence really represents. It turns out that when you dig up a fossil from the dirt, you have to guess as to where that fossil fits into the evolutionary story. The fossil provides you with exactly zero information regarding which other fossils in surrounding layers are related to it. You don’t know which species are it’s great-great-grandparents, nor do you know which species are its great-great-grandchildren. This may be best illustrated with a diagram.
Diagram of Darwin’s so called “Tree of Life” with the evolutionary path of a single species indicated by black arrows and possible “transition fossils” for that species indicated by red boxes.
The figure here shows an example of the Darwin’s “Tree of Life” (a bit irreverent, I know), which represents a theoretical evolutionary “family tree.” In the diagram, I have highlighted the supposed evolutionary history of a single species with dark black arrows. I have also highlighted a few example species with bright red boxes. These represent species we could potentially dig up in the fossil record. If we were to dig those fossils up, we may piece them together into an “evolutionary history” for the species indicated by the black arrows because the fossils look similar or share many similar characteristics.
My point in showing all this is simply to remind us that interpreting the fossil record is exactly that: an interpretation. We may be quite wrong about which species in the fossil record are actually related to each other or how exactly they are related, and we have very little additional information to correct those inferences. That being said, I think there are at least a few key cases we need to consider with respect to “transition fossils.”
While these issues may be valid grounds for continuing to debate what counts as a transition fossil and which fossils truly represent transitionary species, it seems that there are a sufficient number of fossils which live in some kind of “in between” that it is not intellectually honest for us to claim that there are no known transitionary fossils, as is sometimes done.
Birds and Tetrapods
In the following figure, I’m showing two of the better known candidate transition fossils: Archaeopteryx and Tiktaalik. Over 10 fossils of Archaeopteryx have been uncovered, and in all cases, we find both reptilian features (e.g., jaws with sharp teeth and a long bony tail) and bird-like features (broad wings and feathers). This may not be sufficient evidence on its own to demonstrate that modern birds really are the descendants of a small set of ancient dinosaurs, but it is at least worthy of considering seriously and formulating a reasonable response.
Two candidate transitionary fossils: Archaeopteryx (between reptiles and birds) and Tiktaalik (between fish and terrestrial tetrapods).
The second species, Tiktaalik, has come to represent a kind of prime example of a transitionary species, and it has a much more storied past than many other candidate transition fossils. I have chosen to show Tiktaalik specifically because its discovery provides an actual example of reasonable scientific work.
Tiktaalik is considered to be a transitionary fossil connecting fish and land-dwelling tetrapods (four-footed vertebrates). Examination of the handful of fossils which were discovered of this species in the early 2000s revealed that it possessed gills and scales (like a fish) but also appears to have sturdy fin bones, a neck, and a flat, wide head with eye sockets on the top of its head (like the terrestrial tetrapods which supposedly descended from it or a neighboring cousin-species).
The story of Tiktaalik’s discovery begins with the recognition that the oldest tetrapods in the fossil record appeared around 390 Myr ago (known as the Upper Devonian period). In the late 1990s the fact that there were not many (if any) strong candidates bridging the gap between fish and tetrapods was a significant problem for that part of evolutionary theory. At that time, the paleontologist Neil Shubin assembled a team to search for such a species in the exposed shoreline regions (where a fossil transitioning from aquatic to terrestrial life would be expected) of the Upper Devonian geological strata.
(left) Map showing regions with exposed Upper Devonian sedimentary shorelines (in red). (right) Map showing the location where Tiktaalik was uncovered.
Neil and his colleagues consulted the available geological data to locate candidate dig sites meeting these criteria. The identified regions are shown in this map: northern Greenland, northeastern United States, and northern Canada.
It is important to pause here and recognize that at this point, it is possible to formulate a properly scientific “if-then” statement as a hypothesis based on evolutionary theory.
If fossils are retrieved from exposed, Upper Devonian shorelines, then a transitional fossil between fish and tetrapod may be found.
With this hypothesis in hand, Neil and his team set out to test it by digging at an appropriate site. The fossil record of northern Greenland and the northeast United States were both well studied and no candidate transition species had been found in those regions, so Neil and his team selected northern Canada as their dig site. After a few false starts and relocations, they eventually uncovered a handful of fossils of the species shown in the figure above at the location marked by the red ‘X’ on the map, above. They dubbed the species “Tiktaalik,” meaning “large freshwater fish” in the language of a nearby Inuit population.
If the Tiktaalik species truly does represent a transitionary fossil between fish and tetrapods, then we can say that the test outlined in the hypothesis above “failed to falsify” the hypothesis based on evolutionary theory. This is the most one can ever say about the results of any experiment of observation. I know it is underwhelming compared to the claims frequently found in popular scientific literature, such as “special relativity proved by atomic clock experiment” or “Standard Model confirmed by observations at the Large Hadron Collider,” but this more modest claim is also more honest. All that being said, even just these handful of transitional fossil candidates seem like a body of evidence worth considering seriously as honest Christians.
Whales: The Poster Children
Whales are considered one of the best established cases of macroevolution, particularly with respect to the existence of what are considered some of the strongest candidates for transitionary fossils. There are two key attributes of these fossils which are typically highlighted.
Fossils collected in the last decade document the ways in which Cetacea (whales, dolphins, and porpoises) became aquatic, a transition that is one of the best documented examples of macroevolution in mammals.
Whale Origins as a Poster Child for Macroevolution
(Thewissen and Bajpai, 2001)
The first attribute is the location of the nostril on the skull. As biologists are quick to point out, land-dwelling mammals typically have their nostrils at the end of an elongated snout (or at least on the front of their face in the case of apes and humans). However, this is not a great location if you’re a whale. It would be much more convenient if your nostril were located on the top of your head so you could just float up to the surface and take a deep breath of fresh air. The expectation from evolutionary theory would be that this transition from nostrils at the front of the face to nostrils on the top of the head would have taken place over many, many generations. This enables us to formulate a specific hypothesis:
If a transitionary fossil between ancient terrestrial mammals and modern whales and porpoises is found, then its nostril should be located part way between the front of the face and the top of the head.
Representation (based on mostly intact fossils) of the skull of a land mammal (left), a candidate transition fossil (center), and a modern sea-dwelling mammal (right).
Thus, the expectation for a transitionary fossil between land-dwelling mammals and aquatic mammals is a movement of nostril location from the front of the nose toward the top of the head. The figure here shows a set of example fossils showing that with an ancient land mammal (Atriocetus) having its nostril at the end of its nose, an aquatic mammal (Amazon River dolphin) with its nostril located at the top of the head, and a candidate transition fossil (Dorudon) having its nostril located part way between the two. If Dorudon has been correctly identified as living in the evolutionary history of modern whales and porpoises, then this evidence also “fails to falsify the hypothesis.”
The second attribute considered as evidence in favor of evolution is related to the presence of those pelvic bones in modern whales discussed above. If those truly are vestigial organs, inherited from ancient, terrestrial ancestors, then the expectation from evolutionary theory is that an intermediate species would have pelvic and hind-leg skeleton structure somewhere between those of terrestrial mammals and modern whales. Putting this into a clear hypothesis:
If a transitionary fossil between ancient land mammals and modern whales and porpoises is found, then its pelvis and hind legs should be less developed than a land mammal but more than a whale.
There are a handful of fossils are considered strong transitional candidates. The first, and most recently not-extinct, is Basilosaurus isis (34 Myr ago). This image below shows the fossil of Basilosaurus isis as it was discovered in Egypt in 2015, and the callout to the right of that shows the mostly intact hind-leg structure discovered as part of that fossil. Many of the leg-bones frequently present in mammals can be seen here, even if in diminished form.
(left) The skeleton of Basilosaurus isis as it was found in Wadi El Hitan, Egypt (right) A detailed view of the leg bones recovered as part of this skeleton.
The next frequently mentioned candidate is Dorudon atrox (40 Myr ago). The image below shows a reconstructed version of the fossil of that species (I could not find any clear examples of mostly complete Dorudon atrox fossils, as in the case of the Basilosaurus isis). Here, again, if the reconstruction is accurate, you can see the presence of significant hind leg bones.
(left) The skeleton of Dorudon atrox at Senckenberg Museum (right) A zoom in of the reconstructed leg bones for this species.
Although there are several other candidate transition fossils in the history of modern whales, perhaps the most significant is Ambulocetus natans, shown below. In this species, which lived about 48 Myr ago, we see much more developed hind legs, perhaps able to even carry the animal on land while significantly assisting in propelling it through the water. When discussing this particular species, comparisons to an otter are often made where the otter has four functioning limbs, but the hind legs are webbed and positioned in a way that they are able to better swim in the water.
(top) Mostly complete skeleton of an Ambulocetus natans arranged as it was found. (bottom) Attempted reconstruction and assembly of the skeleton.
A quick Critique
Before proceeding with the final line of evidence in favor of evolution, it may be helpful to pause again and consider how this fossil evidence is often presented and discussed. First, it is important to recall that fossils do not provide any information about what other species are their ancestors or which are their successors. Thus, arranging the previous three species into an evolutionary line of succession involves a significant amount of interpretation, even some guesswork. Even if whales evolved from land mammals, it is quite possible that Ambulocetus natans is not part of that evolutionary history. The most we can say for certain is that if our methods for dating fossils are correct, then sometime about 48 Myr ago, there was an animal that looked like its skeletal structure enabled it to walk on land and efficiently swim in water. Then, several millions of years later, another species existed (which may bear no relation to Ambulocetus natans), and that species appeared to have very small hind-legs and mostly swam in the water the way modern whales swim.
(left) Typical graphic showing the supposed evolutionary history of modern cetaceans. (right) Reminder of the actual, likely relationship between the many fossils discovered.
Another important note, the way in which this information is presented often leaves one with the impression that the species shown in the proposed evolutionary history bear many striking similarities which gradually change. It is possible that some of these similarities are the result of trying to present a comprehensible, concise scientific diagram. However, those diagrams may frequently underemphasize the actual differences between the species. For example, in the diagram below, I have highlighted how the Basilosauris isis and the Dorudon atrox are typically presented side-by-side as being closely related steps in the evolution from land mammal to whale. However, this diagram leaves the impression that these two species were quite similar in size, when the reality is quite different. On the right, I have included an inset showing the actual relative sizes of these two species. It turns out Dorudon was about 4 m long while Basilosauris was over 18 m long, more than 4 times the size of Dorudon!
(left) Highlight of Durodon (atrox) and Basilosaurus (isis), shown as being similar in size. (inset) Comparison, showing the actual relative lengths of these two species.
Inset credit: Voss et al. (2019)
DNA Evidence
The final line of evidence we will consider in favor of evolution comes from analysis of deoxyribonucleic acid, better known as DNA. DNA, is the molecular hard-drive of life. It stores all of the basic information necessary to assemble the 20 amino acids into proteins, the building blocks of life. This information is encoded by a series of nucleotides which are arranged along the length of the double-helix structure of DNA.
The nucleus of each cell stores DNA in tightly coiled packages, called chromosomes (shown on the left). Each chromosome is made up of a single, very long strand of DNA with individual nucleotide “letters” arranged along the length of that strand.
It turns out the relevant information for assembling a given protein is not all grouped together on the DNA molecule. Instead, there are often several important portions, called exons, which encode for specific amino acids, and between the exons there are portions of DNA which do not seem to play a role in assembling amino acids into proteins. These “unused” portions of DNA are called introns.
A single gene includes exons (colored regions), which encode for a specific series of amino acids, and introns (uncolored regions between exons), which do not seem to encode for any specific amino acid chains and are unused when assembling a protein, such as insulin.
The fact that the introns are not used for assembling proteins means that a random mutation in those portions of the DNA should not have a significant impact on the rest of the cellular functions.
Similarity in the insulin gene between humans and apes (98%) vs humans and chickens (64%).
This means that while the exon portions of a gene should remain generally unchanged in order for the animal to be healthy, the intron portions are able to change, and those changes can be propagated to future generations. Based on this, and assuming an evolutionary relationship between various animals, we can formulate another hypothesis. Animals (or plants, fungi, etc.) which are believed to be more closely related (i.e., share a more recent “common ancestor”) should have more similar genetic makeup (especially intron portions of genes where there is some flexibility) than animals which are believed to be less closely related. Putting this into a more formal statement:
If species A is more closely related to species B than it is to species C, then the specific genetic sequences of A and B should be more similar than the same genetic sequences of A and C.
In the diagram above, I have shown an example of such a comparison for the gene used to build insulin, comparing two species which evolutionary theorists claim are closely related (humans and apes) and two species which are believed to not be very closely related (humans and chickens). The order of nucleotides agree between humans and apes 98% of the time, whereas the agreement between humans and chickens is only 64%. This, once again, “fails to falsify the hypothesis.”
Evidence Against
I am of the opinion that the evidence presented above is significant and deserves to be considered seriously. There are a wide array of responses a faithful Christian can adopt. Some of these responses are a bit more humble (e.g., “we don’t have enough information to understand everything yet”) while I think others flirt with harmful implications for the character of God (e.g., “God made it look like evolution occurred in order to test your faith”). Regardless of how one responds, I think there are also a significant number of issues facing modern evolutionary theory which also need to be contended with.
Kickstarting Life
Perhaps the most significant problem for evolutionary theory is how one gets from a “primordial soup” of organic chemicals to a fully functioning single-celled organism, capable of reproducing itself. This is a problem which Darwin did not even attempt to tackle. He effectively assumed that some small number of species existed early on, and he didn’t bother to make much of a fuss about how these first species came to be. In fact, the conclusion of On the Origin of Species included the following reflection:
There is grandeur in this view of life, with its several powers, having been originally breathed [by the Creator] into a few forms or into one; and that whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are begin, evolved.
Thus, it seems Darwin was open to the possibility that God specially created a few early life-forms. His argument was about how those primordial species might change and morph over time as some go extinct and new ones emerge.
As for that itching problem, the first single-cell organisms, at the time of Darwin, the view of the microbiological world was very different from what we know today. At that time, the consensus opinion of naturalists (who were just discovering genetics and would never know about the complexities of DNA) was that a single cell was just a bounded basic building block, filled with some cytoplasm and imbued with life-force. Thus, scientists at the time were quite optimistic that it would be possible to create such a living cell artificially, as indicated by statements such as
Jacques Loeb
Nothing indicates, however, at present that the artificial production of living matter is beyond the possibilities of science… we must succeed in producing living matter artificially, or we must find the reasons why this is impossible.
— Jacques Loeb (1912)
What we have discovered since the early 1900’s about the complexities of microbiology make it clear that the leap from “primordial soup” to living cell is quite a tremendous one. I would not fault anyone for supposing it is in fact impossible without some outside force.
In fact, over the past several decades, there have been ongoing efforts to build a single cell artificially. Even armed with all the tools of modern microbiology, the results have been rather underwhelming. At this point, even if a single, fully functioning cell were to be created in the laboratory tomorrow, it would not demonstrate that such a cell can emerge naturally. Instead, it would demonstrate that creating such a cell requires careful intervention from an intelligent being.
If evolution by a purely natural means is to be taken seriously as a possible origin for life, then it must be shown that it is possible for functioning life naturally emerge (with no specific human intervention) from an environment which plausibly existed on the ancient Earth.
Cultural problems
Another problem facing evolutionary theory is the scientific culture surrounding it. As a (recovering) astrophysicist, I am aware of a similar problem with respect to the Big Bang Theory. If you want to have a successful career as an astrophysicist, then you best not critique Big Bang cosmology. Doing so is likely to get you cast aside as a crackpot pseudo-scientist.
This is not good scientific practice. While many critiques of the Big Bang and evolution are based on misunderstandings or poor scientific reasoning, this does not mean that no good critiques exist. I think this problem is well expressed in the often quoted statement from American geneticist and evolutionary biologist, Theodosius Dobzhansky.
Theodosius Dobzhansky
Nothing in Biology makes sense except in the light of evolution
— Theodosius Dobzhansky (1973)
While I can concede that evolutionary theory is potentially able to connect many otherwise disparate sub-fields of biology, I think that such a statement is much too strong and is a reflection of the fact that very few biologists are permitted to question the prevailing evolutionary framework of modern biology without risking career suicide, being tossed out along with “those crazy creationists.”
Irreducible complexity
The final critique I have time to address here is a concept called “irreducible complexity,” which was popularized most powerfully by American biochemist Michael Behe. The concept here is that some systems are irreducibly complex if, in their simplest form, they require several key components to function and removing or significantly modifying one of them causes the whole system to fail. A non-biological example presented by Behe is a mouse trap, which he argues requires five key components: base, spring, hammer, catch, and bait. If one of these pieces are removed or significantly modified, then the trap will not work as intended. If the hammer is removed, then there is nothing to strike the mouse and kill it. If the spring is removed then the hammer does not snap down on the neck of the victim mouse, etc…
Similarly, Behe and others argue that many biological systems are irreducibly complex. One frequently presented example is the bacteria with its flagellar motor. In this case, if the filament is removed, then the motor may rapidly spin, but no propulsion is generated. If any one of the various rings are not concentrically placed in the cell wall, then the motor cannot rotate to spin the filament, etc.
If these systems truly are irreducibly complex, then it is difficult to conceive of a naturalistic evolutionary path for these to arise. A bacteria with a 96% complete flagellum motor maintains very little, if any, evolutionary advantage over a bacteria with a 0% complete flagellum.
Diagram of bacteria with a callout of the details of the flagellum motor. The bacterial flagellum has become one of the best known cases considered to be an irreducibly complex system.
Many biologists have attempted to refute the idea that any such irreducibly complex biological systems truly exist. This conflict is inevitable in the culture which has taken ahold of the modern scientific community. This culture is purely naturalistic, and to admit the possibility that science may not be able to fully explain every phenomenon observed in the natural world is simply not permissible. You can see an example of that cultural conflict unfolding in the clip of a debate between Michael Behe and Kenneth Miller, below. When I view this clip, as a scientist, the debate seems to be impassioned more by a conflict of world views than an otherwise harmless discussion of the specifics of modern biology.
In modern science, it is sadly often the case that if you haven’t deleted God completely from your equations, then you’re not considered a real scientist.
Summary
Because I believe all truth truly is God’s truth, we do not need to fear investigating the claims of modern evolutionary theory. This brief survey of those claims demonstrates considerable evidence that some kind of considerable change has happened to the make up of life on Earth over its storied history.
At the same time, I think there is considerable reason to pause and suspect that a naturalistic description of the history of life does not capture that whole story. We have shown several counterarguments here, and there are more that could be examined with more time and space. These include but are not limited to
Punctuated Equilibrium: evolution sometimes appears to progress extremely rapidly and at other times progress very slowly.
Genetic Step Functions: how can the number of chromosomes in a species can change if the number of chromosomes need to match in a given mating pair (and in the potential mates of their offspring)?
DNA proofreading with DNA polymerase: genetic mutations are generally corrected during DNA replication. It is unclear to me how well this is factored into the expected genetic variation rate necessary to account for the modern understanding of evolution.
As always, whatever the details are, the Bible clearly states that God is intimately involved in the history of life on Earth. That is a fact Christians who take the Bible seriously are bound to affirm, even if the details of what that looked like are unclear from the scientific data.
