Science Literature

The question in the title is asked, and answered, by Gunter Theissen, a geneticist from Friedrich Schiller University Jena. He points out that "many of the biologists criticizing gradualism have been geneticists". These scientists are not looking for a fight with the consensus evolutionary theory, and if the Modern Synthesis were "able to fully explain the origin and diversification of life", they would embrace it.

"Unfortunately, the Synthetic Theory and its contemporary derivatives have major shortcomings, for example in explaining evolutionary novelties and constraints, and the evolution of body plans, which to me appear to be especially interesting aspects of the evolutionary process. As long as population genetic based evolutionary theories such as the Synthetic Theory cannot fully explain all aspects of evolution, scientists as well as lay people will, for good reasons, keep looking for better explanations."

Sssssh! Stop rocking the boat of gradualism! (Source here and here)

The key problem is one of explaining the origin of "evolutionary novelties". Theissen suggests that a major reason supporting Darwin's commitment to gradual change "seems quite trivial". This relates to observations about minor variations in living things and the conclusions he published in his 1859 book.

"Despite Darwin's undeniable merits, explaining how the enormous complexity and diversity of living beings on our planet originated remains one of the greatest challenges of biology."

Gradualism has always been more influenced by ideology than evidence. Lyell's mentoring provided Darwin with spectacles that permitted only the light of uniformitarianism to pass. On the Origin of Species presented Darwin's best case for gradual change, but the verdict of several generations of scholars is that the data speaks otherwise.

"And indeed, up to now the empirical basis of strict gradualism is weak at best. For instance, with its abrupt transitions, the fossil record provides little evidence for a gradual evolution of new forms. Also the branching patterns of higher taxa in both animals and plants as revealed by cladistics and systematics do not support the idea that the major features of body plans and their constituent parts arose in a gradual way. It is not surprising, therefore, that alternatives to Darwin's gradualism have been considered many times during the past one and a half century."
[. . .]
"Advocates of these views often do not completely deny gradual changes (typically during adaptation or microevolution), but consider them unable to explain the origin of phenotypic novelties, or species and higher order taxa."

Theissen's interests revolve around evolutionary developmental biology or "evo-devo". The key thought is that biological novelties usually result from changes in developmental control genes. Whilst closer analysis of an apparently novel structure can sometimes reveal a gradualist mechanism, neoDarwinians are not justified in thinking that they can infer that the same conclusion can be drawn for all structures. (Note, when ID advocates use reasoning like Theissen, it is often described as "the argument from incredulity".)

"So there is always the hope that detailed analysis of the developmental and genetic basis of a phenotypic feature may in the end make it possible to explain its origin in a gradualistic way. This is unlikely to happen in many cases, however, where a reasonable story of continuous change is simply beyond imagination."

Theissen's paper has an interesting set of case studies that are illustrative of his thesis that saltational evolution is a reality. The first set relate to plants and the second set to animals. These are significant arguments, but all too frequently there is a major problem in that relevant data is limited. One, in particular, is worth highlighting: "Cirripedes as the descendants of hopeful monsters". This group, commonly described as barnacles, engaged Darwin's attention for many years (go here). In 2006, a study was published that pointed out the absence of a particular Hox gene abdominal-A in several species belonging to three orders of Cirripedes. This was deemed significant because the gene is present in a sister group, the Ascothoracida. Theissen writes:

"It thus appears likely that the deletion (or substitution) of a homeotic gene resulted in the saltational origin of an organism [. . .] that established a new evolutionary lineage. Based on their data the authors raise the question as to whether Cirripedes are hopeful monsters. However, since Cirripedes represent an old, widely distributed and quite species rich group of animals, they are in my view neither monsters nor just hopeful, but well adapted and successful extant organisms. Therefore, it would be more appropriate to consider Cirripedes as putative descendants of hopeful monsters rather than hopeful monsters themselves.
Is not it ironic that the favourite animals of the hard-core gradualist Darwin may represent an excellent example for non-gradualistic (saltational) evolution?"

No doubt there are many issues that can be usefully discussed here. If there has been a deletion of a homeotic gene that has led to the origin of the Cirripedes, questions about the origins of hox genes and the supporting infrastructure are still unanswered. ID scientists would also like to enquire whether there are design reasons for the lack of this particular gene. But the most relevant discussion points relate to the genuine controversies that are found within evolutionary biology. That the differences are serious is obvious from these comments:

"Few contemporary biologists will doubt that gradualism reflects the most frequent mode of evolution, but whether it is the only one remains controversial. [. . .] In conclusion I argue that the complete dismissal of saltational evolution is a major historical error of evolutionary biology tracing back to Darwin that needs to be rectified."

Contrast these words with some of the forthright affirmations coming from neo-Darwinists.
Alan Lesher, CEO of the American Association for the Advancement of Science: "But there is virtually no controversy about evolution among the overwhelming majority of researchers".
Professor Jerry Coyne, of the Department of Ecology and Evolution at the University of Chicago, rejects all "teach the controversy" initiatives, saying "never mind that the controversy about evolution is not scientific, but social and political."
78 leaders of science and educational associations endorsed these words: "Evolutionary theory ranks with Einstein's theory of relativity as one of modern science's most robust, generally accepted, thoroughly tested and broadly applicable concepts. From the standpoint of science, there is no controversy."

The more discerning commentators will qualify their words and say that whilst there is no controversy over the principle of evolution from a single-celled common ancestor, there is considerable controversy over mechanisms. However, even this stance needs to be critiqued because there is also a scientific debate to be had about common ancestry. One outcome is clear from all this: teachers need to incorporate such thinking into their educational programmes. Those who only want to sweep scientific controversies under the rug of social and political agendas are not representing the science properly to their students. The way to handle controversy is not for the teacher to take sides, but to help students recognise different perceptions of the same data and to develop strategies for evaluating the various positions. When the principle of critical analysis is applied, it means the hegemony of neoDarwinism as establishment science will be over (because it will have to use reasoned arguments rather than an appeal to consensus). Then, perhaps, we can get beyond the hype and the hubris associated with origins and ultimate causes.

Saltational evolution: hopeful monsters are here to stay
Gunter Theissen
Theory in Biosciences, 128(1), 43-51 | DOI 10.1007/s12064-009-0058-z

Abstract: Since 150 years it is hypothesized now that evolution always proceeds in a countless number of very small steps, a view termed "gradualism". Few contemporary biologists will doubt that gradualism reflects the most frequent mode of evolution, but whether it is the only one remains controversial. It has been suggested that in some cases profound ("saltational") changes may have occurred within one or a few generations of organisms. Organisms with a profound mutant phenotype that have the potential to establish a new evolutionary lineage have been termed "hopeful monsters". Recently I have reviewed the concept of hopeful monsters in this journal mainly from a historical perspective, and provided some evidence for their past and present existence. Here I provide a brief update on data and discussions supporting the view that hopeful monsters and saltational evolution are valuable biological concepts. I suggest that far from being mutually exclusive scenarios, both gradual and saltational evolution are required to explain the complexity and diversity of life on earth. In my view, gradual changes represent the usual mode of evolution, but are unlikely to be able to explain all key innovations and changes in body plans. Saltational changes involving hopeful monsters are probably very exceptional events, but since they have the potential to establish profound novelties sometimes facilitating adaptive radiations, they are of quite some importance, even if they would occur in any evolutionary lineage less than once in a million years. From that point of view saltational changes are not more bizarre scenarios of evolutionary change than whole genome duplications, endosymbiosis or impacts of meteorites. In conclusion I argue that the complete dismissal of saltational evolution is a major historical error of evolutionary biology tracing back to Darwin that needs to be rectified.