Evolutionary theory asserts that today’s plants and animals developed from far different ancestral life-forms. The characteristics of populations have changed with time, to produce new species. These changes are believed to be relatively gradual. Scientists believe that a new species may take thousands of generations to become clearly differentiated from its original form. Major transitions, such as going from fish to amphibians, or reptiles to mammals, must have involved millions of years and a whole range of intermediate forms. We intuitively expect to see evidence of these intermediate forms in the fossil record.
Mainstream science says that plenty of such transitional fossils have been found. Young Earth (YE) creationists and Intelligent Design advocates disagree. They cite what Darwin himself wrote in the Origin of Species (6th Ed., pp. 341-342), “The number of intermediate varieties, which have formerly existed must be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps is the most obvious and serious objection which can be urged against the theory.”
Thus, transitional fossils are a significant part of the evidence for or against evolution. It is necessary to have a correct understanding of the nature of transitional fossils, in order to properly evaluate the physical evidence. Four factors which impact the nature of fossil intermediates are described below.
First, a little vocabulary: living organisms are grouped together in various levels. From highest level (most inclusive) to lowest, these are: domain, kingdom, phylum, class, order, family, genus, and species. Below species there are strains or sub-species. All animals are grouped in one kingdom, and all plants in another. These are mainly human constructs forced onto the messy biological world, and scientists can legitimately differ on how any particular organism should be classified. A common definition for a plant or animal “species” is the largest group of organisms capable of interbreeding and producing fertile offspring.
Four Key Factors Governing the Transitional Fossil Record
(1) The fossil record is inherently very sparse. Very, very few of all the organisms that have died in past eons become fossilized. As we can observe today, nearly all carcasses rot or are eaten by scavengers rather than being buried intact in rock layers. Of the remains that do get fossilized, many are later eroded away if the rocks in which they are embedded are raised above sea level. If these rocks become deeply buried, the fossils can become smeared beyond recognition in metamorphic transformations. This is even more of an issue for older rock layers, such as the Paleozoic era (Cambrian through Permian periods), since they have had more time to be either raised up to the surface for erosion or to be buried more deeply. Also, of all the potential fossil-bearing rocks, only a small fraction is available in surface exposures for paleontologists to examine.
As Wikipedia points out, “The number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived.” No fossils have yet been found for about a third of the 30+ phyla of living animals. Occasionally (e.g. once every 15 million years or so) we find a rock formation such as the Burgess Shale where conditions were just right to preserve a rich assemblage of fossils (including many soft-bodied animals) in that locale at that snapshot in time. These “Lagerstatte” are the exceptions which prove the rule: they confirm that the ancient seas were teeming with diverse life-forms, but in most times and in most places (i.e. apart from these very rare fossil-rich formations), these organisms simply did not become preserved as recognizable fossils.
The Coelacanth order of fishes furnishes a classic example of the fickleness of the fossil record. These fish were once widespread in the ancient seas. Coelacanths peaked in the fossil record about 240 million years ago, and then declined. The most recent known fossil dates back to about 80 million years ago. It was thought that they had become extinct. In 1938, however, a live coelacanth was discovered in the Indian Ocean. Since then a number of others have been caught. Unless we are prepared to claim that an Intelligent Agent supernaturally re-created these modern coelacanths, we must acknowledge that some population of these fish has existed for the past 80 million years but without leaving a trace in the fossil record.
We should expect to observe many gaps like this in the fossil record. Here is a list of other “Lazarus taxa” which disappear from the fossil record for millions of years, but appear again later.
(2) New species tend to develop in small, isolated populations. The arithmetic of basic population genetics shows that it is more difficult for new genetic mutations to become established in very large populations, than in small populations. This is readily confirmed by laboratory studies. For instance, Perfeito et al. found that new beneficial mutations were much more readily established in small populations of bacteria than in large populations.
Thus, it is far more likely that a new species would develop within a small, isolated population, especially if that population is under some environmental stress that would favor genetic changes. The odds of us finding fossils from that small, localized population is are nearly zero. If the new species becomes more fit than the old species, the new species will expand, and only then is likely to appear in the fossil record. But once a species is widespread and successful in its ecological niche, there will be diminished selection pressure for changes, so fossils of this now well-adapted species are likely to appear for perhaps million of years with showing little change.
(3) A given population can persist for many millions of years with little morphological change. As demonstrated by the longevity of the coelacanth group, a specific type of organism can persist for tens of millions of years with only modest changes. Thus, if we find a fossil of some species in rocks dated as being, say, 100 million years old, it is quite possible that a similar, related species (same genus or family) also existed 110 million years ago, and maybe even 150 million years ago, whether or not we have found these older fossils yet. For instance, the past 80 million years would constitute such a “ghost” lineage for coelacanths.
(4) Evolutionary lineages tend to be “branchy”. Typically what shows up in the fossil record are organisms on the side branches, rather than the directly ancestral ones along the main “trunk” of the family tree. These side branch species often show intermediate features, but are not the actual transitional fossils.
Horse Evolution: Example of Branching Lineage
The evolution of today’s horse (genus “Equus”) from a tiny ancestor is well-supported in the
fossil record. Hyracotherium (sometimes called Eohippus, i.e. “Dawn Horse”) lived in the forests about 55 million years ago. It stood roughly 18 inches (50 cm) tall at the shoulder, resembling a small dog. Its teeth were adapted to eating fruit and soft foliage, and its feet and leg bones were quite different from today’s steeds that thunder across the plains and eat tough grass. The graphic on the right depicts some of the changes in teeth, toes, and overall body size.
The picture below, from the Florida Museum of Natural History, shows how the size and shape of fossil horse skulls has changed with time:
In her article at TalkOrigins on horse evolution, Kathleen Hunt shows a more complete family tree (grouped at the level of genus), with even more branches than depicted in the figures above:
Hunt notes a number of clear, graduated changes that appear in this fossil series. For instance, Hyracotherium (“Eohippus”) had only three grinding molars on each side of its jaw, Orohippus had four, Epihippus had five, and Mesohippus had six grinding “cheek teeth.” That looks pretty “transitional” to me. Although a clear line of descent can be drawn between Eohippus and today’s horses, Hunt cautions that the fossils show a complex pattern, not a unidirectional trend:
Horse species were constantly branching off the “evolutionary tree” and evolving along various unrelated routes. There’s no discernable “straight line” of horse evolution. Many horse species were usually present at the same time, with various numbers of toes, adapted to various different diets…Tracing a line of descent from Hyracotherium to Equus reveals several apparent trends: reduction of toe number, increase in size of cheek teeth, lengthening of the face, increase in body size. But these trends are not seen in all of the horse lines. On the whole, horses got larger, but some horses (Archeohippus, Calippus) then got smaller again. Many recent horses evolved complex facial pits, and then some of their descendants lost them again. Most of the recent (5-10 My) horses were three-toed, not one-toed, and we see a “trend” to one toe only because all the three-toed lines have recently become extinct.
In his general article on transitional fossils, Keith Miller offers these observations on the horse lineage:
Interestingly, some critics of evolution view the record of fossil horses from “Eohippus” (Hyracotherium) to Equus as trivial. However, that is only because the intermediate forms are known. Without them, the morphologic distance would appear great. “Eohippus” was a very small (some species only 18 inches long) and generalized herbivore (probably a browser). Besides the well-known difference in toe number (four toes at front, three at back), “Eohippus” had a narrow elongate skull with a relatively small brain and eyes forward in the skull. It possessed small canine teeth, premolars, and low-crowned simple molars. Over geologic time and within several lineages, the skull became much deeper, the eyes moved back, and the brain became larger. The incisors were widened, premolars were altered to molars, and the molars became very high-crowned with a highly complex folding of the enamel.
The significance of the fossil record of horses becomes clearer when it is compared with that of the other members of the order Perissodactyla (“odd-toed ungulates”). The fossil record of the extinct titanotheres is quite good, and the earliest representatives of this group are very similar to “Eohippus“. Likewise, the earliest members of the tapirs and rhinos were very “Eohippus“-like. Thus, the different perissodactyl groups can be traced back to a group of very similar small generalized ungulates.
Expectations for Fossil Lineages
Figure 1 represents a naïve expectation of what the fossil record should look like for the evolutionary family tree encompassing some species A through D. In this figure, there is a single lineage, with the direct ancestors all appearing as fossils. Each earlier form neatly disappears from the fossil record as the next one appears, so there are no overlaps. From the four factors discussed above, it is obvious why Figure 1 is not realistic, yet this is what YE creationists often demand to see.
Figure 2 shows a more realistic fossil lineage. The points of actual divergence (common ancestors) are relatively unlikely to have left fossils. It is more probable that we will find fossils of successful populations on the side branches of the family tree, such as B and C in this figure. This is not due to some weakness in evolution. Rather it is due to the intrinsic nature of speciation and fossil preservation (branching, new species arising in small populations, etc.).
While this diagram shows the branching which is characteristic of evolutionary lineages, it is unrealistic in depicting the rate of morphological change as being roughly constant with time. As noted above, evolutionary changes tend to happen relatively quickly in small populations that do not leave a trace in the fossil record, while large successful populations can continue with only modest changes for many millions of years. (By “relatively quickly” we mean that a new genus might develop in a million years or so for vertebrates, and of course in shorter times for organisms with faster reproductive rates.)
Figure 3 below better represents the type of fossil pattern we expect from what is known about speciation and fossilization:
The thick vertical lines denote the chronological extent of the fossil remains for the four species A–D. There are fossils of B and C which display some characteristics which are intermediate between A and D. However, some of these fossils do not appear in strict morphological order. All of the extant fossils of C predate all the fossils of B, even though the morphological progression suggests that B would be in some sense ancestral to C. Some fossils of D appear at the same time as fossils of C.
YE creationists sometimes claim these “out of order” fossils represent some sort of dire problem for evolution. This claim is false. This type of pattern is exactly what is predicted by the four factors discussed above. Populations like A, B, C, and D that actually appear in the fossil record are likely to be large and stable. But there will always be an earlier time, before these populations expanded (or when geological conditions did not favor preservation), when each of these populations was present but was not represented among the known fossils. It is entirely plausible that a common ancestor between B and C existed sometime before the earliest fossils of C, even though the lineage from that ancestor up to the B fossils has not yet been observed in the rock layers.
A possible family tree for these fossils is shown above in Figure 4. The thick lines denote the observed fossils, with the thin lines denoting inferred lineage relationships.
Another potential family tree for the same fossils is shown above in Figure 5. It shows a slightly different pattern of splits from common ancestors. How can we determine which lineage pattern is a better fit to the fossil evidence?
Arthropods: Example of Fossil Family Tree
There is a whole field of study called cladistics where scientists ponder these questions. They define and analyze various characteristics of physical features in fossils, and also genetic relations among living species. Here is an example of the type of thinking that goes into cladistics, centered on the evolution of arthropods (think: bugs) about 500 million years ago. Dennis Venema at Biologos writes:
All living arthropods have a suite of defining characteristics such as a hard external skeleton (exoskeleton), specialized body segments, and specialized appendages. While these characteristics are useful for defining modern arthropods, these criteria become less useful as we travel back through the evolutionary history of arthropods. The reason is simple – from an evolutionary point of view, one would not expect these different traits to arise as a unit in one fell swoop. Rather, one would expect that these traits would arise over time in the lineage leading to modern day arthropods. [Thus] we would expect to find species in the fossil record that do not have the full suite of “arthropod” characteristics, but only some:
For example, based on the above phylogeny we might expect to find two groups of “arthropod-like” organisms in the fossil record: species that have only (1) of the three traits (specialized appendages only), as well as a second group (2) with specialized appendages and segments. …these species would represent “transitional forms” in the sense that they have intermediate sets of characteristic features that indicate the steps the arthropod lineage took to achieve the “modern” suite of characteristics.
And in fact, this sort of pattern is reflected in the fossil record. The figure below, from Legg, et al., shows that the ancient fossils are consistent with sequential modifications in appendages and body segments as populations developed from early arthropod-like forms to full modern-type arthropods. Here, modern arthropods (e.g. Hexapoda [insects], and Crustacea [crabs, etc.]) are shown at the bottom, with the earliest evolutionary branching at the top. For instance, Anomalocaris had large compound eyes and hardened specialized appendages, but it did not have a hardened exoskeleton over its whole body. It is considered a transitional “stem” arthropod, not a full-fledged “crown” arthropod. Each point (1, 2, 3, etc.) represents the appearance of a key innovation, such as compound eyes, arthropodized limbs, arthropodization of the trunk exoskeleton, etc.
The cladistic relationships in this figure were not just randomly proposed to rationalize the fossils. Nick Matzke described the rigor that went into constructing this diagram:
These researchers, and the previous researchers that they are building upon, identified 580 individual, variable characters, each of which has to be identified, defined, divided up into discrete character states, and encoded. This laborious process had to be repeated for (in this) case 173 fossil [or living] taxa… A lot of fossils are missing a lot of characters – typical and expected in paleontological analyses – but it is still a lot of work. After this, one runs a cladistic or other phylogenetic analysis… and calculates support statistics. …Almost any biological dataset typically has extremely statistically significant tree signal, and this is true whether or not it agrees precisely with other analyses, and whether or not all relationships of interest to the researcher are precisely resolved with high support.
Fish-To-Tetrapods: A Missing Link Is Found?
400 million years ago, the seas were teeming with various types of fish, most of which lived entirely underwater, and had fairly flimsy fins. By about 365 million years ago, fossil evidence exists for primitive tetrapods, such as Acanthostega and Ichthyostega. These creatures had four limbs which could support some weight and assist in moving around in shallow water, although they probably could not readily walk around on dry land. How did fish evolve into tetrapods? Besides the development of limbs, the bones of the head had to change from two parts to one, and the solid head/body connection in a fish was replaced by a flexible neck.
The leading candidates among fishes for tetrapod ancestry are the “lobe-finned” fishes. The bottom fins of these fishes are arranged in pairs and supported by internal bones, which would facilitate the evolution of these fins into legs. Also, the lobe-finned fishes of the Devonian period were already able to breathe air, when necessary, via “spiracles” in their skulls.
Various lobe-finned fish fossils have long been known, where the skeletal structures of the fins include primitive versions of the bones found in the limbs of later, terrestrial animals. Examples include Eusthenopteron and Panderichthys, whose remains have been dated to about 380 million years ago. While these fossils hint at evolutionary pathways toward tetrapods, these are still very much like regular fishes. It would be gratifying to discover a fossil species with more pronounced tetrapod-like features.
In 1999 a team of scientists led by Neil Shubin of the University of Chicago set out to find such a transitional fossil. Since the main fish-tetrapod fossil gap was in the 363-380 million year range, they decided to focus on an exposed formation of rocks in the Canadian Arctic which were of that age, and which had been deposited in a shallow freshwater environment. The team kept digging year after year. In 2004 they were rewarded with the discovery of remains of a fish they named Tiktaalik. While Tiktaalik is firmly on the fish side of the fish-tetrapod divide, it has an impressive suite of tetrapod-like features.
This was a dramatic vindication of evolutionary theory. A key test of any scientific theory is the ability to make novel predictions which can be experimentally verified. Operating within the conceptual framework of mainstream geology (an old earth) and biology (common ancestry), Shubin’s team picked one location to excavate, and found the type of fossil (previously unknown) that they had predicted. There is nothing in YE creationism or Intelligent Design which could produce such a precise and novel prediction.
According to Wikipedia, the mixture of both fish and tetrapod characteristics found in Tiktaalik include:
Fish – Fish gills, fish scales, fish fins
“Fishapod” – Half-fish, half-tetrapod limb bones and joints, including something like a wrist joint, and radiating, fish-like fins instead of toes
– Half-fish, half-tetrapod ear region
Tetrapod – Tetrapod rib bones and lungs
– Tetrapod mobile neck with separate pectoral girdle
In 2014, Shubin and co-workers published details on the pelvic girdle and fins. Again, features intermediate between fishes and tetrapods are evident:
The pelves of Tiktaalik are paired and have broad iliac processes, flat and elongate pubes, and acetabulae that form a deep socket rimmed by a robust lip of bone. The pelvis is greatly enlarged relative to other finned tetrapodomorphs. Despite the enlargement and robusticity of the pelvis of Tiktaalik, it retains primitive features such as the lack of both an attachment for the sacral rib and an ischium.
The figure below from Ahlberg and Clack shows the differences in skeletal and other features among the fossils species discussed above. There is a gradual loss of the gill cover (blue), and a reshaping of the skull.
The following figure by Kevin Padian, reproduced by Anastasia Thanukos, shows more details in the fins and limbs of these transitional species. A progression is seen from 8 to 7 to 6 digits, as intermediates between fish fins and the 5 digits found in living tetrapods. No particular timescale is given for the ghost lineages that predate the fossil appearance of these species.
Source: K. Padian, Integra Comp Biol 2008; 48: 175-88, reproduced in A. Thanukos, Evolution: Education and Outreach 2009; 2: 84-89.
The discovery of Tiktaalik does merit accolade, but there is a danger of overstating its role. Some science popularizers have referred to this fish as our “ancestor.” It bears repeating that all the species shown here are dead-end side-branches of evolutionary lineage. As indicated by a careful examination of the figures above, none of them is directly ancestral to living tetrapods. What they do show is that a variety of fishes with some tetrapod characteristics, and a number of early tetrapods with some fish-like features, were present in the geologic strata that predate the appearance of the fossils of modern-type tetrapods. This amount of transition fossil evidence is about what we would expect here, if tetrapods actually did evolve from lobe-finned fishes. This era was over 350 million years ago, which is a lot of time for continents to rise, fall, split, and crash, all of which could destroy early fossils or make them inaccessible.
To bring the tetrapod story up to date, in 2010 Niedźwiedzki et al. published on the discovery of what appear to be tracks of an unknown tetrapod in rocks in Poland that are dated to 397 million years ago. This is about 30 million years before the earliest known primitive tetrapod fossils such as Acanthostega and Ichthyostega. Possible tetrapod tracks, dated to 385 million years ago, have also been found on Valentia Island, off the coast of Ireland. Debate remains over whether these trackways were made by genuine tetrapods. If they were, that pushes the transition from fish to tetrapods some 30 million years earlier than previously believed. YE creationists have claimed that this is a problem for evolution, but it is not. It merely extends the ranges of Tiktaalik, Acanthostega, etc. somewhat further than originally thought.
Friedman and Brazeau have analyzed the patterns of tetrapod-related Devonian fossils, and find evidence that only a small fraction of those species that existed are represented in the known fossils. The preservation rate of species there is about an order of magnitude sparser than for, say, Cenozoic mammals in North America. Thus, it is “unsurprising” that there are “outstanding stratigraphic gaps in the Devonian tetrapod record.”
Below is shown a phylogram from Niedźwiedzki et al. of selected lobe-finned fishes and stem tetrapods, which incorporates these trackway findings. Here Pan= Panderichthys, Tik=Tiktaalik, Aca= Acanthostega, Ich= Ichthyosteg, and Tul = Tulerpeton.
Another possibility is that at least some of the early Devonian trackways were made, not by tetrapods walking on (almost) dry land, but by fish scooting along on their fins in shallow water. King, et al. in 2011 published a study of how some modern lungfish can use their pelvic fins in an alternating pattern to “walk” on the sea floor, with the whole rest of their body held off the bottom. Polish trackway PGI 1728.II.15 (Figure 2 c.) in the Niedźwiedzki paper looks like what a pair of fins might do – – it seems that this trackway was made by a single pair of appendages (not four limbs), with the two appendages sometimes alternating and sometimes pushing along in parallel.
Reptiles to Mammals
The reptile-to-mammal evolution has an interesting twist. There are striking differences between the jaw and ear bone structures of reptiles and of mammals. Reptiles have at least four bones in the lower jaw , while mammals have only one; but reptiles have only one middle ear bone, while mammals have three (the hammer, anvil, and stapes). Studies of developing embryos indicated that two of the bones which, in a reptile get incorporated into a reptilian jaw, in a mammal become part of the middle ear.
This had scientists in the early twentieth century wondering what kind of evolutionary intermediate could possibly have maintained adequate hearing and jaw function as these two bones gradually moved from the jaw (in reptiles) to the ear (in mammals). The full story is found in the magisterial “29+ Evidences for Macroevolution” article by Douglas Theobald at TalkOrigins.
In the course of the twentieth century a range of fossils were found which documented many stages of the migration of these bones. At one point, there were actually two independent pairs of jaw joints. This was an essential feature that allowed jaw movement while these bones were in intermediate positions.
On the right is one diagram from the TalkOrigins article which illustrates this transition. It shows a side view of three idealized skulls of mammals, therapsids (mammal-like reptiles), and pelycosaurs (early reptiles). The migration of the bones coded purple, yellow, and blue are clear. The location of the jaw joints is shown as black dots. For the therapsid intermediate form, there are two jointed bone interfaces for the jaw.
Do Transitional Fossils Prove Evolution?
We have shown for a number of cases, that the fossil record is consistent with evolution, given the four factors (sparse fossil preservation, speciation in small populations, etc.) discussed above. The little changes from one species to the next are not accessible, and direct lineal ancestors are typically not found. However, for a typical major transition a range of “cousin” fossils are found which manifest key intermediate characteristics, in the appropriate time range for that transition. For most objective observers, this constitutes strong supporting evidence for evolution. It certainly shows that the fossil record is not a “problem” for evolution.
What do YE creationists make of these facts? To grind through all the claims and debunking here would take a whole book, so I will just note a few issues. One YE creationist response is to put forth some “fact” which seems to disprove the evolutionary case. Since the horse evolution is so clearly evidenced in the fossils, this seems to call for extra effort by the anti-evolutionists. One such “fact” which has appeared on dozens of YE creationist sites is that the fossils of Hyracotherium (“Eohippus”) are not from an ancient horse ancestor, but are merely the bones of a form of the modern “hyrax” (which lives in the Middle East and looks like a rabbit). This claim is debunked on TalkOrigins here.
Another such “fact” promulgated by YE creationists is that fossils of Hyracotherium and modern Equus have been discovered in the same rock layer. This also is false.
Over the course of the last 150 years of fossil collection and classification, it is inevitable that some mistakes would be made by scientists along the way. For instance, a hundred years ago the figures in most science textbooks showed a single, clean, uniform lineage from little four-toed Hyracotherium to big, one-toed Equus. As noted above, the full picture is more complex than that, with various branching, dead-end lineages, some of which co-existed with each other. Various scientists since 1950 have acknowledged that the earlier simplistic picture of horse evolution was not accurate. YE creationists have taken these statements out of context to make it seem like even “evolutionists” admit that the fossil record does not support evolution.
Deceitfully quoting real scientists is common among YE creationist writers. This “quote mining” enterprise takes statements out of context, and (often making generous use of ellipses) carefully carves out just the words that give the desired effect. There is a large section ( the “Quote Mine Project”) of the TalkOrigins site dedicated to exposing these misleading quotations.
That said, let us circle back to such a quote that we noted at the beginning of this essay: “”The number of intermediate varieties, which have formerly existed must be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps is the most obvious and serious objection which can be urged against the theory.”
This quote from Darwin’s Origin of Species is presented endlessly on YE creationist web sites as an admission by Darwin that the facts were against his theory. What the creationists typically fail to include is the very next sentence, in which Darwin tells why this is NOT a problem for his theory: “The explanation lies, as I believe, in the extreme imperfection of the geological record.” This is exactly correct, as we have explained above.
In the next paragraph after these words, Darwin displays a subtle grasp of the nature of likely fossil lineages:
In the first place, it should always be borne in mind what sort of intermediate forms must, on the theory, have formerly existed. I have found it difficult, when looking at any two species, to avoid picturing to myself forms DIRECTLY intermediate between them. But this is a wholly false view; we should always look for forms intermediate between each species and a common but unknown progenitor. [emphasis in the original]
This “common but unknown progenitor” corresponds to the lineal common ancestors which, as noted above, are unlikely to be found as fossils.
These quotes of Darwin occur in the tenth chapter of The Origin of Species, which is appropriately titled “On The Imperfection Of The Geological Record” . Darwin concluded this chapter: “I look at the geological record as a history of the world imperfectly kept and written in a changing dialect. Of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved, and of each page, only here and there a few lines. Each word of the slowly-changing language, more or less different in the successive chapters, may represent the forms of life, which are entombed in our consecutive formations, and which falsely appear to have been abruptly introduced. On this view the difficulties above discussed are greatly diminished or even disappear.” Right again.
Darwin acknowledged that there were not millions of finely-graded intermediate fossils lying everywhere, yet still a reasonable number of significant transitional fossils had been found. He wrote in Chapter 11 of the 6th edition:
As the accumulation of each formation has often been interrupted, and as long blank intervals have intervened between successive formations, we ought not to expect to find, as I attempted to show in the last chapter, in any one or in any two formations, all the intermediate varieties between the species which appeared at the commencement and close of these periods: but we ought to find after intervals, very long as measured by years, but only moderately long as measured geologically, closely allied forms, or, as they have been called by some authors, representative species; and these assuredly we do find. We find, in short, such evidence of the slow and scarcely sensible mutations of specific forms, as we have the right to expect.
… I have attempted to show that the geological record is extremely imperfect; … that only certain classes of organic beings have been largely preserved in a fossil state; … that, owing to subsidence being almost necessary for the accumulation of deposits rich in fossil species of many kinds, and thick enough to outlast future degradation, great intervals of time must have elapsed between most of our successive formations; …that varieties have at first been local; and lastly, although each species must have passed through numerous transitional stages, it is probable that the periods, during which each underwent modification, though many and long as measured by years, have been short in comparison with the periods during which each remained in an unchanged condition. These causes, taken conjointly, will to a large extent explain why—though we do find many links—we do not find interminable varieties, connecting together all extinct and existing forms by the finest graduated steps. [emphases added]
These citations show that sound reasons for the relative paucity of intermediate fossils (i.e. the inherent sparseness of the fossil record, the likelihood that evolutionary changes mainly take place in small local populations, branching lineages, etc.) were clearly stated in The Origin of Species. My article here has merely fleshed out what Darwin wrote more than 150 years ago. There is therefore no excuse for opponents of evolution who assert or imply that Darwin was acknowledging an actual weakness in his theory.
Varieties of Skepticism
The fossil record is clearly compatible with evolution. Indeed, the same can be said for all physical observations, in geology, biology, chemistry, and genetics. The hard reality, though, is that a dedicated YE creationist will not be convinced of macroevolution by any physical evidence. No matter how many fossil intermediates he is presented with, he will always find a way to wiggle out. He can say, “Yes, there is a sequence of fossils with gradually varying characteristics, but you can’t prove that one evolved into the next; you are just assuming evolutionary relationships among them.” Or, “How do you know that God did not miraculously create these species in this sequence?”
I had some critical things to say about YE creationist Ken Ham’s presentations during his recent debate with Bill Nye. However, I appreciated Ham’s honesty about the basis of his convictions. When he was asked the question, “What, if anything, would ever change your mind?”, he responded: “Well, the answer to that question is ‘I’m a Christian.’ And as a Christian, I can’t prove it to you but God has definitely shown me very clearly through his word and shown himself in the person of Jesus Christ. The bible is the word of God. I admit that that’s where I start from… And so as far as the word of God is concerned, no, no one’s ever gonna convince me that the word of God is not true.” This exemplifies the attitude which renders YE creationists largely impervious to the evidence.
Most Intelligent Design (ID) advocates are motivated by the same sort of conservative Christian faith as YE creationists, but they are not as forthright about their methodology. They claim to be “detecting design”, driven solely by the scientific evidence, but in practice Intelligent Design reduces to the classic god-of-the-gaps. Many Christians find it heartening to learn of various gaps in our current understanding of evolutionary history, as though that somehow demonstrates the necessity of God. Unfortunately, ID consistently overstates the magnitude of these knowledge gaps, relying on deceptive half-truths (e.g. with chimp and gorilla genomes, “junk” DNA, and the Cambrian explosion) to make its case.
ID proponents generally accept the mainstream geological dating of the fossils, which puts them in a quandary: if all those intermediate horse fossils between 5 and 55 million years ago did not result from evolution, how did they get there? If all those reptile-to-mammal transitional fossils back in the Mesozoic do not represent natural evolutionary development, how did they get there? It seems that the Intelligent Agent must have poofed all these species into existence (in a sequence that would later deceive us humans into thinking they had evolved), or else the Agent reached in and physically tinkered with their DNA to make it mutate in unnatural ways. YE creationists may be OK with poofing, but ID advocates are stuck. Since they try to maintain a scientific façade, (ironically) they cannot credit their Intelligent Agent with any actual, specific agency.
Most authors at major YE creationist organizations have some depth exposure to the data of geology and genetics and paleontology. They must actively engage in deception in order to portray these data as compatible with a young earth and incompatible with naturalistic evolution (e.g. see here on Grand Canyon geology).
However, the bulk of the 46% (per recent Gallup poll) of Americans who believe that humans were specially created by God a few thousand years ago are simply going along with their traditional beliefs, reinforced by what they hear from the YE creationist mouthpieces. Furthermore, the evidence for evolution is not as obvious to laymen as they would like to see. We scientists can point to lots of circumstantial evidence, where evolution fits the observed patterns. However, we cannot show a new phylum evolving before their eyes, or even in the course of a 50-year experiment. Nature just does not provide that satisfying level of demonstration of the ability of unguided evolution to cause huge but viable changes in living things in a short time-frame.
What the layman sees with his eyes are animals reproducing “after their kind”, with only minor changes. Scientists can, of course, offer valid reasons for this state of affairs (“Evolution happens to be a really slow process”; “The fossil record is inherently sparse”), but these can come across as lame excuses to someone who is predisposed to doubt evolution.
For perspective, my wife (who is well-educated, but not as a scientist) has commented that, to her anyway, the evidence for evolution seems similar to the nature of the evidence for the Christian faith. By that she meant that there are sound documentary grounds (e.g. some of the letters of Paul) to believe that within a decade of the purported resurrection of Jesus there were people going around risking their lives proclaiming that they had encountered the risen Christ; we have a universe that came into existence at a certain point in time; millions of people today testify to a life-enhancing experience of God; there are videos of extraordinary healings in answer to prayers in the name of Jesus (some of which I have described here and here). These factors are all consistent with the gospel, but do not constitute mathematical proof. (I won’t delve into why God may have set things up such that people must come to Him freely, as opposed to being bludgeoned into faith by frequent miracles or apparitions).
I have read of atheists who sweep aside all the circumstantial evidence that exists in favor of God, and demand to see some miracle like an amputated limb growing back before their eyes. This is unreasonable, at least in relation to the Christian God, since Christ clearly stated that on-demand signs will not be given to unbelievers (Matthew 12:38-39). It is thus similar to the demand of YE creationists to see some spectacular demonstration of accelerated macroevolution. (I suspect that, if these demands were actually met, both the hardcore atheist and the hardcore YE creationist would find some way to discount their experience so as to maintain their previous positions.) My point here is not to justify YE intransigence, but to note that all of us to some degree fit the facts in around our existing opinions.
Addressing the Underlying Issues
A key error of YE creationists is to hold that their interpretation of the Bible is the only valid one. They claim that the only faithful reading of the Genesis creation account is a wooden literalism, and that the six “days” of creation in Genesis 1 were necessarily 24-hour solar days. That is simply not true.
The 24-hour day interpretation was represented among the early church fathers, but it was not the only one. Cyprian (c. 250 A.D.) saw these days as 1000-year ages, Origen (c. 225 A.D.) saw them as figurative, and Augustine sagaciously averred that nobody knows for sure: “What kind of days these were is extremely difficult or perhaps impossible for us to conceive” (City of God 11:6, c. 419 A.D.).
A broad swath of contemporary evangelical Christians (especially in the U.K.), as well as many Orthodox believers and a billion Roman Catholics, hold that a recent, six 24-hour-day creation is not the only faithful Christian view. Evangelist Billy Graham has no problem with God using evolution to accomplish His creative purposes for mankind:
I think that we have made a mistake by thinking the Bible is a scientific book. The Bible is not a book of science. The Bible is a book of Redemption, and of course I accept the Creation story. I believe that God did create the universe. I believe that God created man, and whether it came by an evolutionary process and at a certain point He took this person or being and made him a living soul or not, does not change the fact that God did create man. … whichever way God did it makes no difference as to what man is and man’s relationship to God.
For YE creationists to let go of their false beliefs on the age of the earth, they must either (a) renounce their Christian faith altogether, or (b) find a way to reconcile core Christian beliefs (e.g. those asserted in the Nicene Creed) with the facts of science. Many young adults do reject their faith upon exposure to the evidence of geology and biology, after having been told by parents and pastors (and Ken Ham) that evolution and an old earth are flatly incompatible with the Bible.
Option (b) is, of course, less disruptive. If one is willing to acknowledge that the Bible regularly makes use of metaphor, story-telling, and other figurative language (e.g. Jesus’ parables and Nathan’s confrontation with David), that opens up various options for viewing the Genesis story as meaningful without being literal history. I have outlined here the understanding of Scripture that I have come to, along with links to related resources.
While most YE creationists are driven by their peculiar Bible literalism, the key motivation for the Intelligent Design folks at the Design Institute is more cultural or philosophical. In their foundational “Wedge” document they spell out their dismay over “materialism”, and blame Darwin (among others) for a range of modern problems, up to and including the abuses of communism:
…thinkers such as Charles Darwin, Karl Marx, and Sigmund Freud portrayed humans not as moral and spiritual beings, but as animals or machines who inhabited a universe ruled by purely impersonal forces and whose behavior and very thoughts were dictated by the unbending forces of biology, chemistry, and environment. This materialistic conception of reality eventually infected virtually every area of our culture, from politics and economics to literature and art…. Materialists denied the existence of objective moral standards, claiming that environment dictates our behavior and beliefs. …Materialists also undermined personal responsibility by asserting that human thoughts and behaviors are dictated by our biology and environment. … In the materialist scheme of things, everyone is a victim and no one can be held accountable for his or her actions….Finally, materialism spawned a virulent strain of utopianism. Thinking they could engineer the perfect society through the application of scientific knowledge, materialist reformers advocated coercive government programs that falsely promised to create heaven on earth.
There may be some valid points here, but attacking evolution is not going to fix the problem (“materialism”) that the Design Institute is worried about. Here is why: Every human alive today was conceived and grown by strictly materialistic processes. We can watch sperms fertilize eggs and see the egg cells divide; we can in large measure track the biochemical processes behind all this. The growth of neuronal networks in the fetal brain unfolds without supernatural invention. Every mental event corresponds to some array of physical events in the brain, which in turn are subject to the usual laws of physics. These are the key facts that anti-materialists have to deal with.
Whether or not scientists are able to explain every twist and turn of evolution does not touch these currently-observed facts. Thus, ID’s campaign of sowing doubt about evolution cannot possibly accomplish its avowed goal of unseating materialistic philosophies.
If ID supporters grasped this fundamental point, that could cause the ID movement to refocus in a constructive way. That would be a welcome development, since currently the Intelligent Design movement squanders financial and intellectual resources that might be employed in engaging the real issues with materialism.
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