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  Since then, some gaps have been replaced by thin bridges of intermediary forms.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.

     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.