Chapter 6 Theories on Rapid Evolution | Gaps in the Fossil Record | Higher Taxa | Saltation | Punctuated Equilibrium | Stasis is Data | The Problem Remains

"Gaps"

The observation that new forms and structures appear suddenly in the fossil record is old news.  The difficulty posed by "missing links" or "gaps" in the fossil record was acknowledged even by Darwin himself:

"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 gravest objection which can be urged against my theory.  The explanation lies, as I believe, in the extreme imperfection of the geological record." 1 

Darwin thought the gaps in the fossil record exist because the record is incomplete, and that subsequent discoveries might fill in the gaps.  To a degree, he was right.  Since then, some gaps have been replaced by thin bridges of intermediary forms.  Yet even where these bridges connect forms in a parent-descendent relationship, the pattern of sudden appearances, or rapid transformation into new forms, has not changed.  After 150 years of new discoveries, the pattern is firmly established and recognized.  As Clarkson asserted,

"What is seen in the rocks is not the result of the fossil record's inadequacy, but a fair picture of the actual pattern of events." 2

Even George Gaylord Simpson, who championed the Darwinian opinions of the Modern Synthesis, candidly admitted the problem,

"It is a feature of the known fossil record that most taxa appear abruptly.  They are not, as a rule, led up to by a sequence of almost imperceptibly changing forerunners such as Darwin believed should be usual in evolution." 3

These so-called "gaps" in the fossil record are a timeless centerpiece of creationist arguments.  As Eldredge and Gould put it,

"The rarity of transitional series remains as our persistent bugbear.  From the reputable claims of a Cuvier or an Agassiz to the jibes of modern cranks and fundamentalists, it has stood as the bulwark of anti-evolutionist arguments." 4

Yet by emphasizing the "gaps," the creationists de-emphasize the fossil links that have been found, thereby only giving half the picture.  Evolutionist Robert Carroll gave a more complete picture by acknowledging the pattern of suddenness, yet also making a case for evolutionary change where evidence exists for it.  With regard to sudden appearances, he stated,

"Instead of showing gradual and continuous change through time, the major lineages appear suddenly in the fossil record." 5 

"The same basic evolutionary pattern applies to all groups for which there is an adequate fossil record." 6 

"New discoveries are unlikely to change our general understanding of large scale patterns of evolution." 7 

"Instead of new families, orders, and classes evolving from one another over long periods of time, most had attained their most distinctive characteristics when they first appeared in the fossil record and have retained this basic pattern for the remainder of their duration." 8

Yet Carroll also found examples of gradual evolution in conformity with Darwinian expectations.  He described the gradual and directional evolution of ichthyosaur paddles over their 100 million year tenure, as well as gradual and directional changes in mammal teeth during the Pliocene. 9  He also proposed that late Jurassic pleurosaurs evolved gradually from the late Triassic sphenodontids. 10 

Likewise, Levinton also acknowledged a "morphological discontinuity among taxa," 11 yet, like Darwin, postulated, "missing data, rather than saltations (leaps), are the likely explanations." 12     

Even Gould, who was usually on the opposite side of the fence from the gradualists, acknowledged a documented case wherein gradual speciation had occurred over a period of 2 million years from one species of Melanopsis to another. 13

Thus, although many evolutionists admit that there are "gaps" in the fossil record, this does not by itself justify creationists' attempts to use their words to attack evolution, nor to support the notion that God formed each species as an unrelated lineage, as Genesis 1 repeatedly insists, "each after its own kind." 14  Although there are "gaps" in some cases, gradual evolution certainly does happen in other cases.

Higher Taxa

The anomaly has always been, and still remains, the sudden origin of the higher taxa.  As Clarkson put it,

"The links between higher taxa are obscure, and are but poorly represented in the fossil record… but what the fossil record does give us is many examples of the 'instantaneous' origin of new structural plans… the origination of higher taxa, in this sense, remains the least understood of paleontological phenomena." 15 

The phrase "higher taxa" refers to the broader groupings of life forms.  For example, mammals, birds, and reptiles are higher taxa than cows, pigeons, and alligators. 

From lower to higher taxa, humans are classified as

• sapiens (species) – (lowest)
• Homo (genus - plural is genera)
• Hominids (family)
• Primates (order)
• Mammals (class)
• Chordates (phylum – plural is phyla)
• Animals (kingdom) – (highest)

 With regard to human evolutionary lineage, the lower taxa show a pattern of gradual transitions, for there are a multitude of fossils that are progressively more and more human-like and less and less ape-like, which demonstrate human evolution happened gradually.  However, at the higher taxa, the order primates appeared suddenly, without a gradual line of fossils connecting it to an earlier group of mammals.  It is this puzzle, the origin of higher taxa, which has proven the most difficult question. 

Saltation

Natura non facit saltum.  "Nature does not make sudden leaps."That statement is among the most sacred scriptures of Darwinism.  But during the first half of the 20th century, a large group of evolutionists adopted a theory named after the word saltum, meaning "sudden leaps."Called "Saltationists," they defied Darwin, asserting that Natura facit saltum – "Nature does make sudden leaps."An evolutionist named Schindewolf was among their proponents.  Schindewolf expressed the conviction that gaps in the fossil record would remain regardless of whatever new discoveries are made:

"The missing links of the cliché have never been found… the closed evolutionary lineages which we have before us regularly break off as we near their roots.  Nothing in the future will change this." 16 

Schindewolf pointed out that when dramatically different life forms first appear in the fossil record, they cannot be traced to known ancestors by small incremental steps of evolutionary change.  Rather, they appear suddenly, as "large evolutionary steps, without connecting transitional links." 17  The clean break in the traceability of ancestry is most acute at the root of the higher taxa:

"All decisive transformations of the basic structures of the higher-ranking types are brought about in large, individual steps with far-reaching consequences, without links or transitions, in early ontogenetic stages." 18

The beginnings of Saltationism can be traced to Hugo DeVries who lived at the turn of the 20th century. 19  At the core of Saltationist theory is the notion that sudden macro-mutational events can radically alter the DNA sequences of reproductive cells, thus causing a very speedy injection of new genetic material, the result of which is a new species.  In other words, your sperm 'n' eggs get zapped so hard by some sort of excessive radiation that your kids are born as mutants.  Then, by means of multi-generational inbreeding, your kids procreate a new and better species.  Another Saltationist, Goldschmidt, dubbed these hypothetical mutants "hopeful monsters."  The idea is that a macro-mutation, which is not immediately lethal, could conceivably be tweaked by natural selection over a few generations into something useful.

Saltationism is so reviled among some evolutionists that it is called "heresy."  It is now dead and buried somewhere in the intellectual trash pile of the scientific community, mostly on account of its genetic impossibilities.  The large-scale genetic mutations it requires are too harmful for the production of viable mutants.  Evolutionary genetics favors slight mutations, not macro-mutations. 

Yet despite the collapse of Saltationism, the paleontological observations which originally constituted the basis for it have not gone away.

Punctuated Equilibrium

After the conventional wisdom of the Darwinists had silenced the Saltationists, it was just a matter of time before a new theory of rapid evolution was formulated to explain the sudden appearance of new forms.  In 1972, Niles Eldredge and Stephen Jay Gould published such a theory.  It has gone down in history as Punctuated Equilibrium, and it remains the most widely held theory of rapid evolution today.

The two words, "Punctuated" and "Equilibrium," refer to two separate phases within the lifetime of a given species.  In the first phase, the evolution of a species is "Punctuated" – meaning that most of the evolutionary change occurs over a short time period.  Second, there is a long period of relatively little change, called "Equilibrium" or "stasis."  As Eldredge and Gould put it,

"Most evolutionary changes in morphology occur in a short period of time relative to the total duration of the species." 20

One example of Punctuated Equilibrium in action was provided by a study of African mollusks from the Turkana Basin.  3,300 individual mollusks across 13 different lineages were measured.  Williamson concluded,

"The Turkana Basin sequence clearly conforms to the punctuated equilibrium model: long-term stasis in all lineages is punctuated by rapid episodes of phenotypic change.  No gradualistic morphological trends occurred in any lineage." 

When change did happen, speciation events were completed within 5,000 to 50,000 years. 21

Punctuated Equilibrium can also be observed in the Huaqiao Formation in Hunan, China.  Layers of rock record the sudden arrival of half-a-dozen or so new species, which exist for a while before being replaced by other suddenly emerging species.  Cycles of spontaneous arrival of new species happen several times in the formation. 22

Another documented occurrence of Punctuated Equilibrium in the fossil record comes from the analysis of 14,000 conodonts over 10 million years of Ordovician time in Argentinean strata.  Albanesi and Barnes found that stasis had been punctuated by a brief period of speciation from one type of tooth-like structure to another.  They hypothesized that the cause of the speciation was genetic isolation coupled with deposits of volcanic ash into the conodont's habitat.  Within 230 meters of rock, there was no change; then, in less than one meter, the transformation from one type of dentical to another was complete – representing a period of 50,000 to 100,000 years.  This was correlated to Gould's earlier estimate that marine invertebrate species usually last for 5 to 11 million years, and that the punctuation phase of their evolution generally accounts for only 1% of that time, 23 which pleasantly agrees with the 50,000 to 100,000 years they calculated for the time in which the punctuation event occurred. 24 

The 50,000 to 100,000 years that they calculated for the time it took one species to evolve into another is consistent with the findings of other studies.  Geary's study of Miocene gastropods suggested that a punctuation event that led to speciation happened in "tens of thousands of years." 25  Goodfriend and Gould found that the pulmonate genus Cerion morphed from one species into another in no more than 15,000 to 20,000 years. 26  Therefore, Punctuated Equilibrium supposes that evolution happens in the tens of thousands, not millions, of years.  Although considerably shorter than traditional Darwinists suppose, tens of thousands of years is not exactly the six days mentioned in Genesis 1.  Punctuated Equilibrium cannot support creationist suppositions.

Some evolutionists were angered by the theory of Punctuated Equilibrium, not so much because of its scientific merit, but rather because it was presented as an alternative to Darwinism, which inadvertently resulted in creationists presenting it as evidence against evolution in general – an unwelcome consequence that Eldredge and Gould tried to mitigate. 

Stasis is Data

The primary pillar for the theory of Punctuated Equilibrium is the reality of stasis in the fossil record.  Species tend to remain essentially unchanged for long periods of time, often extending for millions or even tens of millions of years without altering their anatomy.  As Gould put it,

"Stasis is data… The fossil record may, after all, be 99 percent imperfect, but if you can, nonetheless, sample a species at a large number of horizons well spread over several million years, and if these samples record no net change, with beginning and end points substantially the same, and with only mild and errant fluctuation among the numerous collections in between, then a conclusion of stasis rests on the presence of data, not on absence!" 27

Gould documented a multitude of examples of stasis, wherein a large number of individual fossils within a species, sampled over long time increments, revealed a picture of relatively little or no net change.  Gould summarized evidence for stasis from a large variety of fossilized life forms – trilobites, beetles, lungfish, cheilostomes, scallops, brachiopods, and certain ungulates such as wildebeasts. 28  Some of these examples of stasis are based on extraordinarily plentiful data.  For example, stasis is the norm among nearly all of the more than 330 invertebrate species that existed over a period of 9 million years in the Devonian times of the Appalachian Mountains. 29  Some might say these were merely fossilized hillbillies that were incapable of evolution; notwithstanding, the shear multitude of data points among these Appalachians is a good indication of the reality of stasis. 

Stasis is the "equilibrium" part of Punctuated Equilibrium, and often it is the only part of a species' evolutionary history that can be observed, because the period of stasis is so much longer than the period of punctuation, that only fossils from the period of stasis have been preserved. 

Richard Dawkins, a critic of Punctuated Equilibrium, attributes punctuations to migrations, not to rapid evolution:

"When we look at a series of fossils from any one place, we are probably not looking at an evolutionary event at all: we are looking at a migrational event, the arrival of a new species from another geographical area." 30 

However, the difference between a migrational event and a punctuational event can be distinguished when the punctuational event has fossil intermediaries in a formation.  In fact, Eldredge's first discovery of a punctuation event was characterized by just that – parent and child species, together with intermediaries, all in a single formation.   He found that a certain species of trilobite called Phacops milleri dominated lower Hamilton formations for 3 or 4 million years.  It consistently had 18 columns of lenses in its eyes.  The entire time period with regard to P. milleri was characterized by a "simple lack of change." 31  Then, very abruptly, that trilobite was replaced by another very similar trilobite called Phacops rana, which remained unchanged for 7 or 8 million years thereafter. 32 

The replacement was too abrupt, and the periods of stasis too long, for a gradual transition to be possible.  At first, there were no intermediaries, and so Eldredge, like Dawkins, attributed the phenomenon to migration, not macromutation.  However, there was one formation in New York, where intermediary forms did exist.  They were present in a quarry, and occurred enough to discern that the evolutionary event was completed in just 1,000 to 10,000 years' time. 33  Once the change was complete, the new species branched out to new locations, replacing the earlier species, and it remained essentially unchanged for millions of years thereafter. 

We may draw certain conclusions from Punctuated Equilibrium.  Among them,

• Species stay essentially unchanged for millions of years. 
• When species do evolve, they evolve within thousands of years, not millions. 
• The degree to which they evolve is small and produces only a slightly different descendent species.            

The Problem Remains

This third conclusion, namely that Punctuated Equilibrium explains only small evolutionary changes, should draw our attention, for it means that Punctuated Equilibrium does not necessarily solve the bigger problem regarding the sudden appearance of higher taxa.  This, I think, should give us pause, for it tends to limit the applicability of Punctuated Equilibrium to the level of the lower taxa, and leaves us still curious about the higher taxa.  Eldredge himself hinted at the matter, speaking about Phacops rana,

"Hardly prodigious, this degree of anatomical retooling falls well within the bounds of "micro-evolution" – loosely speaking, the kind and degree of relatively minor change that marks the difference between closely related species." 34

The sudden appearance of new and completely unparalleled forms is the great problem.  Where are the missing links from archosaurs to pterosaurs?  From mustelids to sea lions?  From Ediacaran fauna to the Cambrian Explosion?  Punctuated Equilibrium seems to only address small changes from species to species – not from order to order, class to class, or phylum to phylum, and therefore does not answer the most pressing question about the origin of higher taxa.  The examples of Punctuated Equilibrium that can be garnered from the fossil record – the snails, the conodonts, the trilobites – all these are examples of minor species-level changes.  Although Punctuated Equilibrium is an excellent framework for explaining small evolutionary changes at the level of the lower taxa, it is not necessarily directly pertinent to the bigger problem regarding the sudden appearance of higher taxa.

If the change brought from a punctuation event is small, as every indication testifies, then an accumulation of Punctuated Equilibrium cycles are required before a quantum leap from one phylum, class, or order can be realized.   And if these punctuations are most often separated by long periods of stasis, then would not the emergence of new phyla, classes, and orders be, as a matter of the big picture, gradual? 

The accomplishments of multiple Punctuated Equilibrium cycles over time should therefore yield a gradual advancement not too different from what Darwin originally envisioned – a slow and steady progress, characterized by punctuations, yes, but each of such a small scale and with such infrequency as to be barely distinguishable from the "big picture" of phyletic gradualism.  The alternation between stasis and punctuation yields a very slow rate of progress over time.  It still falls short of explaining the sudden emergence of the higher taxa.  For even though a punctuation at the level of species or genus, such as Phacops was, could be quite speedy; however, the subsequent period of stasis is not speedy, and therefore if we wish to use the framework of Punctuated Equilibrium to explain, for example, how the trilobite's relatives became spiders, we must assume it happened over a long period of time, for a large number of punctuations followed by periods of stasis must have occurred to make it happen.

The three figures below plot amounts of evolution over time.  Notice that both Darwinism and Punctuated Equilibrium yield an overall pattern of gradual evolution.  Even though Punctuated Equilibrium is characterized by fits and starts, it still necessarily takes a long time to accomplish significant evolutionary change at the magnitude of higher taxa.  That is because stasis separates punctuations, and because punctuations only accomplish small amounts of change.  Both traditional Darwinism and Punctuated Equilibrium contrast sharply with what the fossil record actually demands, for the fossil record frequently does not allow for the gradual evolution of higher taxa. However, if we postulate that several punctuations occurred in rapid succession, then perhaps we have an answer.  For if the punctuations were very numerous and followed each other in quick succession, occurring with greater frequency, and with shorter periods of stasis intervening between them, this might explain the sudden appearance of the higher taxa. We might call it "Punctuated Punctuationalism," in which the "Equilibrium" part of the process is skipped or greatly abbreviated.  If this model works in tandem with Punctuated Equilibrium, then rapid succession of punctuations is followed by long periods wherein punctuations are comparatively infrequent.  If this is the case, we might interpose a staircase upon the quantum leap, such that sudden leaps are explained by the summation of smaller punctuation events.  A graphical example is below.

Yet for this to happen, one must consider the series of population bottlenecks that would follow each punctuation event, for the bottlenecks would rapidly deplete the gene pool and make species vulnerable to further selective pressures.  As with the case of the dark and light colored moths mentioned earlier, the more selection kills off the ill-adapted members of a species, the more that species looses its genetic variety.  The more it looses its variety, the less able it is to make further adaptations. 

Moreover, every time a species is nearly killed off in a bottleneck, the population declines, which significantly increases the chances of inbreeding.  This brings harmful recessive alleles to the surface, where they kill their carriers and thus exterminate even more variety from the gene pool.  The mutations that enable evolution to occur get killed off before transposable elements can reshuffle them and make them useful.

The question is, can the mechanics of population genetics support a series of population bottlenecks associated with several punctuations in rapid succession, and still retain enough genetic variety to effect a mega-evolutionary transition on the order of magnitude required to explain the sudden appearance of higher taxa? 

Yet even if it were genetically plausible, we are still left with another question – what caused the series of punctuations in rapid succession to begin with?

Pareiasaur to Proganochelys, the punctuated evolution of Turtles - American Museum of Natural History