Saturday, 27 December 2014

The Fossil Evidence for Common Descent 1: Missing Links and other Special Creationist Fallacies

In the 154 years since Darwin published the first edition of The Origin of Species, the fossil evidence for evolution has increased considerably. In particular, we can demonstrate the evolution of tetrapods from lobe-finned fish, whales from terrestrial mammals, birds from dinosaurs, and humans from primates to a degree that would have astonished earlier palaeontologists. While the nature of speciation and the sheer improbabilities involved in dead animals being fossilised and then found mean that the fossil record will always be an imperfect record, what we have demonstrates the reality of large-scale evolutionary change beyond reasonable doubt. 

Despite this, special creationists still continue in their desperate attempts to wave away the evidence. Given that practically no special creationists (and certainly no Christadelphian science denialists) are palaeontologists, their arguments invariably hinge on quote mining mainstream scientists, peddling out-of-date arguments which betray a lack of familiarity with the contemporary scientific literature, or advancing ideas about 'missing links' that indicate a failure to recognise that evolution is a tree, not a ladder.

Part 1 will look at the general class of mistakes made by special creationists when attacking the fossil record, while the remaining parts will look in detail at notable evolutionary transitions (such as fish to tetrapod and dinosaur to bird) for which the fossil evidence is beyond rational dispute.

Evolution is not a ladder but a tree

The fundamental special creationist misconception is the belief in evolution as a ladder, with single celled life at the bottom rung, with all other life arranged progressively on higher rungs from worms to fish to amphibians and so on with mammals on the top rungs and humans at the top. Coupled with their quote mining of Darwin's remarks that as "innumerable transitional forms" are not found "embedded in countless numbers in the crust of the earth", this forms the basis of the special creationist claim that evolution cannot be true because of the alleged lack of transitional fossils.

The evolution of life is modelled not as a ladder, but as a tree, something that is obvious when we think of the pattern that develops when the process of descent with modification from an original ancestral population is mapped out. We start with an ancestral population that diverges into more than one group, with each successor group in turn likewise diverging, and so on:

The diagram of divergence of taxa presented by Charles Darwin in On the origin of species (1859)

Looking for relationships, not missing links

Thinking of evolution as a ladder rather than as a tree drives the erroneous special creationist belief that the fossil record should abound with missing links, whose alleged absence is seen as lethal for evolution. This of course is the fundamental error made by special creationists. As evolutionary biologist Louise Mead points out:
The concept of a “missing link” is an “archaic expression”… tracing back to the Great Chain of Being, a view of the physical and metaphysical world as an unbroken chain. It was later temporalized by the evolutionary thought of the eighteenth and nineteenth century to the idea of evolution as a progressive climb up a ladder… These views of evolution create the false expectation that there should be fossil evidence showing “a complete chain of life from simple to complex”. [1]
Of course, given that all existing forms of life share a common ancestor, and have been evolving for the same length of time since their ancestral lineages diverged from the common ancestor, there is no such thing as 'primitive' and 'advanced' forms of life. Related to this is the 'platypus fallacy' which argues that early branching equals primitive. Genomics expert T.R. Gregory neatly skewers this error, made in the context of those using traits of modern species to infer details about the evolution of others, such as humans:
The fallacy here is to assume that the non-human species is “primitive”, such that it can be used as a proxy for a distant human ancestor. This is a fallacy because “primitive” and “derived” refer to individual traits, not entire species, and because the comparison being made is between two modern species, not an ancestor and a descendant. Both lineages have, by definition, been evolving for exactly the same amount of time since diverging from a common ancestor. 
I am going to call this the “Platypus Fallacy”, based on an example that I have used in my lectures. Consider the following quote, by one of the authors of the platypus genome sequence paper:
“The platypus is a very ancient offshoot of the mammal tree, so it was 166 million years ago that we last shared a common ancestor with platypuses, and that puts them somewhere between mammals and reptiles, because they still maintain quite a lot of reptilian characteristics that we’ve lost; for instance, they still lay eggs. So we can use them to trace the changes that have occurred as we went from being a reptile, to having fur to making milk to having live-born young.”
Now, if a platypus were asked to summarize the situation, he could just as well say this:

“The lineage of which humans are a part is a very ancient offshoot of our mammalian family tree, so it was 166 million years ago that we last shared a common ancestor with humans, and that puts them somewhere between mammals and reptiles, because they lack a lot of specialized characters that we have gained but the ancestral amniote also lacked; for instance, they have no electroreception, no bills, no webbed feet, and no venom. So we can use them to trace the changes that have occurred as we went from being a reptile, to having fur to making milk to having our specialized features.”
Of course, if a platypus did say such a thing, I hope his colleagues would encourage him to avoid committing the “Human Fallacy”. [2]
This confused thinking underlies the creationist assertion that (for example) modern reptiles are the ancestors of modern animals, or that palaeontologists are looking for 'missing links' that are halfway in morphology between modern mammals and modern reptiles. This overlooks the fact that representative animals early in the lineages of modern reptiles and modern mammals would have looked nothing like their modern descendants. 

This leads on to the second misconception, and that is the belief that palaeontologists are looking for the common ancestor of major lineages. This betrays considerable ignorance about how evolutionary biologists and palaeontologists reconstruct evolutionary family trees. Mead again:
The ancestor of two living forms is unlikely to be found alive because it would have been outcompeted in most cases by newly adapting forms, and an extinct ancestor of two living forms would not be expected to look intermediate between them. Today, evolutionary biologists and paleontologists do not focus on finding “intermediates” but rather on reconstructing evolutionary relationships and history using shared derived characters or synapomorphies. Willi Hennig revolutionized systematics in the 1960s with the introduction of cladistics, which ushered in a new method of phylogenetic analysis and a new approach to systematics. Instead of relying on a Linnaean system of classification, cladistics placed the focus on evolutionary history, specifically identifying features as ancestral (general) or derived (evolved after the lineage split from the ancestor). If a shared derived character or synapomorphy is found in two or more related organisms, it is inferred to have been present in their common ancestor, irrespective of whether or not there is a fossil record for that ancestor... Rather than trying to find the actual fossil corresponding to the “missing link” between lobe-fins and tetrapods, paleontologists instead look for fossils with characters or features important for an adaptive transition from life in an aquatic environment to life on land and that are shared as the result of common ancestry. [3]
Any special creationist attack on evolution that fails to understand phylogenetic systematics, and how it guides palaeontology is wrong before it starts, as it is attacking a straw man version of palaeontology.

What about punctuated equilibrium?

Special creationist attacks on the fossil evidence for evolution invariably pit 'punctuated equilibrium' against a gradualist view of evolution that creationists believe demands (and is falsified by the lack of) "innumerable transitional forms. These attacks ignore the fact the fossil record reflects what one would expect under a model of allopatric speciation. As evolutionary biologist Douglas Theobald points out in an excellent overview of punctuated equilibrium: 
  1. There are two common uses of "gradualism," one of which is more traditional, the other of which is equivalent to Eldredge and Gould's "phyletic gradualism." 
  2. Darwin was not a "phyletic gradualist," contrary to the claims of Eldredge and Gould.
  3. PE [punctuated equilibrium] is not anti-Darwinian; in fact, the scientific basis and conclusions of PE originated with Charles Darwin. 
  4. PE does not require any unique explanatory mechanism (e.g. macromutation or saltation).
  5. Eldredge and Gould's PE is founded on positive evidence, and does not "explain away" negative evidence (e.g. a purported lack of transitional fossils). [18]
The value of Theobald's paper goes well beyond providing an overview of PE; as I pointed out earlier, under a model of allopatric speciation, we would expect to have the fossil record we have, which falsifies the claims that there is an inherent contradiction between what evolutionary biology predicts and what the fossil record. Theobald is worth quoting at length not only to point out this fact, but to show that any claim that Darwin was a 'phyletic gradualist' (i.e. believing that the fossil record must show innumerable fine traditions) is false:
Eldredge and Gould based their theory of PE on the neontological theory of allopatric speciation (especially the allopatric theory of Ernst Mayr, which he called "peripatric" speciation) (Mayr 1963, 1971). For instance, in the same paper under the section "Implications of allopatric speciation for the fossil record," they state, 
"We wish to consider an alternate picture to phyletic gradualism [i.e., PE]; it is based on a theory of speciation that arises from the behavior, ecology, and distribution of modern biospecies. ... the allopatric theory has grown in popularity to become, for the vast majority of biologists, the theory of speciation." (Eldredge and Gould 1972) 
Further down, Eldredge and Gould continue: 
"In summary, we contrast the tenets and predictions of allopatric speciation with the corresponding statements of phyletic gradualism previously given:  
(1) New species arise by the splitting of lineages. 
(2) New species develop rapidly. 
(3) A small sub-population of the ancestral form gives rise to the new species. 
(4) The new species originates in a very small part of the ancestral species' geographic extent - in an isolated area at the periphery of the range.  
These four statements again entail two important consequences:  
(1) In any local section containing ancestral species, the fossil record for the descendant's origin should consist of a sharp morphological break between the two forms. .... we will rarely discover the actual event in the fossil record. 
(2) Many breaks in the fossil record are real; they express the way in which evolution occurs, not the fragments of an imperfect record." (Eldredge and Gould 1972) 
These tenets and conclusions of their "new" theory of PE are quite interesting when compared to these quotes from Origin of Species
PE tenet #1 and #2
"If, however, the modified offspring of a species get into some distinct country, or become quickly adapted to some quite new station, in which child and parent do not come into competition, both may continue to exist." (Darwin 1872, Ch. 4, "Natural Selection," p. 155) 
This quote shows that Darwin understood tenet 1 above in the description of allopatric speciation. It also indicates that Darwin realized that species could develop rapidly (tenet 2 of PE), as he says they may "become quickly adapted." Also, 
PE tenet #1,#2 #3, #4, and PE consequences #1 and #2
"... the periods during which species have undergone modification, though long as measured by years, have probably been short in comparison with the periods during which they retained the same form. It is the dominant and widely ranging species which vary most frequently and vary most, and varieties are often at first local—both causes rendering the discovery of intermediate links in any one formation less likely. Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they have spread, and are discovered in a geological formation, they appear as if suddenly created there, and will be simply classed as new species." (Darwin 1872, Ch. 15, "Recapitulation and Conclusion", p. 619) 
This quote is remarkable in that it nearly states every tenet and prediction that Eldredge and Gould listed for their paleontological treatment of allopatric speciation. Darwin agreed with the other tenets of allopatric speciation, including tenets 3 and 4 - "varieties are often at first local" and "will not spread ... until they are considerably modified." Furthermore, it is obvious that Darwin agreed with the two predictions of the allopatric speciation model concerning what will be found in the paleontological record.  
Here I present quotes from The Origin of Species, Chapter 10, "On the imperfection of the geological record," that basically sum up the conclusions of PE: 
"When we see a species first appearing in the middle of any formation, it would be rash in the extreme to infer that it had not elsewhere previously existed. So again, when we find a species disappearing before the last layers have been deposited, it would be equally rash to suppose that it then became extinct. We forget how small the area of Europe is compared with the rest of the world ... when we see a species first appearing in any formation, the probability is that it only then first immigrated into that area." (p. 423)  
"... varieties are generally at first local; and that such local varieties do not spread widely and supplant their parent-form until they have been modified and perfected in some considerable degree. According to this view, the chance of discovering in a formation in any one country all the early stages of transition between any two forms is small, for the successive changes are supposed to have been local or confined to some one spot." (pp. 427-428)  
"... it might require a long succession of ages to adapt an organism to some new and peculiar line of life, for instance, to fly through the air; and consequently that the transitional forms would often long remain confined to some one region; but that, when this adaptation had once been effected, and a few species had thus acquired a great advantage over other organisms, a comparatively short time would be necessary to produce many divergent forms, which would spread rapidly and widely throughout the world." (p. 433) 
It is obvious from all of these quotes that Darwin did not think the "gaps" between fossil species were only due to geological processes, but that they are a direct consequence of natural speciation processes. Phyletic gradualism is a strawman when attributed to Darwin, and this is one of the reasons why so many evolutionary biologists reacted strongly to the initial presentation of the hypothesis of PE. Furthermore, it is erroneous even to claim PE as an original concept, since all of the tenets of allopatric speciation and the conclusions labelled as PE were stated by Charles Darwin over 100 years before Eldredge and Gould proposed their "novel" hypothesis.
In other words: (1) the fossil record reflects what we would expect under a model of allopatric speciation (2) there is no essential conflict between the fossil record and the modern synthetic theory of evolution and (3) Darwin anticipated PE, making any claim that 'Darwinism' and PE are in conflict nonsensical.


As shown, the special creationist attacks on palaeontology are made based on a profound ignorance of the subject they are criticising. Sadly, it's straw men all the way. What is particularly depressing is to see members of our own community make these elementary mistakes in their attacks on evolution. In a poorly researched article in the November 2009 edition of The Christadelphian, John Morris claimed without any justification that "[m]issing links are still missing!" [5] His use of the term 'missing link aline betrayed considerable lack of familiarity with evolutionary biology, a point he conceded with his admission that "[f]ew of us have advanced qualifications in the relevant sciences, and if we fail to hold our own in discussions about fossils, for example, or if we reveal our ignorance of current molecular biology, we shall be deemed to have lost the contest!" One would imagine that if one fails to hold his own in discussions with an expert, it means the view the special creationist holds has been falsified, and should be abandoned. Unfortunately, the tendency is to privilege a flawed, human interpretation of the Bible above hard evidence from the natural word, a view which is nothing other than the gross error of fideism.

The following parts will show just how solid the evidence for evolution from the fossil record is, in order to disabuse those who have mistakenly placed their trust in special creationist error why nothing in biology makes sense except in the light of evolution.


1. Mead L.S. "Transforming Our Thinking about Transitional Forms" Evo Edu Outreach (2009) 2:310-314

2. Gregory T.R. "The Platypus Fallacy" Genomicron June 3 2012

3. Meade, op cit p 311

5. Morris J "Darwin or the Gospel" The Christadelphian November 2009