Introduction

The sentiment that as time goes by, things get more complex has been with us a long time. Most of us have at some time heard about Aristotle and Plato's Great Chain of Being, stretching from the crystals, proceeding over worms, and culminating in the splendor of Man - Christian philosophers later added some chains to make room for the angels and God. Although neither Aristotle nor his Christian followers intended the Chain to represent any progression in time, early evolutionists adopted the metaphor to illustrate the progression of life.

Darwinism is often recognized as having disposed of this idea, and every biologist will be able to list several examples of organisms being secondarily simplified; flightless beetles having lost their wings, snakes having lost their limbs, and silly creationists having lost their brains. But while it is true that Darwinism allows for complex structures being reduced, it is equally true that there exists a certain innertia for taking the simple to represent the primitive. After all, if Darwinism is true, every organism possessing some structure must have descended from an organism lacking it. There is thus the incentive to take simplicity as a sign of primitiveness. Darwin, for example, suggested that the simple swim bladder had been converted into lungs (1859, 190-1), but today we know that swim bladders are actually simplified lungs (see Gould's essay in Eight Little Piggies for a lucid account).

In this essay I will review various cases in which simplicity has been erroneously equated with primitiveness. In neither of these cases did Darwinism raise any doubts about the result, and probably played a big role in its acceptance. My purpose in doing this is not just to criticize Darwinism, but also to shed light on some misconceptions that has arisen in discussions over intelligent design.

Microsporidia

Consider the Microsporidia, part of the taxon Archezoa, thought to be a remnant of primitive eukaryotes (Keeling 1998). Eukaryotes are characterized by a number of features, including their mitochondria, and when a number of organisms lacking mitochondria were discovered, they were naturally regarded as representing a primitive, pre-mitochondrian state. In addition to mitochondria, the Microsporidia also lacks peroxisomes, Golgi bodies, and even cilia. Furthermore, their ribosomes were the same size as those found in bacteria. To top it all off, the basic prediction of the pre-mitochondrian Micropiridia hypothesis was fulfilled: Initial molecular phylogenies placed it at the root of the eukaryotic tree, branching off earlier than the mitochondria-bearing members (Vossbrinck et al. 1987). Surely, a beautiful example of a Darwinian hypothesis being tested and confirmed by the data?

Well, things soon began to get a little more complicated. You see, Microporidia are parasites, and parasites are known to experience streamlining selection. The possibility that their simplicity was simply the result of a secondary reduction became very real with the discovery that they possessed an insertion shared only by animals and fungi (Kamaishi et al. 1996), and later phylogenies based on tubulins supported a relationship with fungi (Edlind et al. 1996; Keeling & Doolittle 1996). The final nail in the coffin was the discovery that Microporidia contained genes from mitochondria, indicating that they once possessed them, but subsequently lost them (Germot, Philippe & Le Guyader 1997; Hirt et al. 1997).

Placozoa

Represented by a single species, Trichoplax adhaerens, scraped off the glass wall of an aquarium in an Austrian laboratory in 1883, Placozoa is one of the more remarkable of the metazoan phyla. They have less DNA than any other animal, and with their only four cell types (sponges, in comparison, has 10-20 different types) they are considered the morphologically most simple animals (Grell and Ruthmann 1991). Consequently, they were placed on the basal branches of phylogenies, with Eumetazoa as a sister group (Zrzavý et al. 1998; Peterson & Eernisse 2001). As two researchers recently remarked, "Trichoplax adhaerens represents the morphologically most simply organized multicellular animal known, and thus has often been seen as the "living ancestor" of all metazoans." (Ender & Schierwater 2003, 130).

This view, however, is in conflict with the molecular data, which consistently places Placozoans among the more derived metazoans (Abouheif, Zardoya, & Meyer 1998; Collins 1998, 2002; Kim, Kim, & Cunningham 1999; Peterson & Eernisse 2001). If this is the case, Placozoa must have undergone an extreme degree of reducing selection, losing such non-trivial features as "specialized muscle cells, nerve cells, and a fixed anteroposterior axis" (Jenner 2004, 374).

The type III secretory system

The eubacterial flagellum has been cited as an obstacle to Darwinian evolution (Denton 1985; Behe 1996). In response to this, many Darwinists, primarily writing on internet discussion boards, have raised the type III secretory system as illustrating a step in the evolution of the flagellum. The secretory system is employed by bacteria for transporting proteins into other cells, which can either harm the receiver or establish a mutualistic symbiosis, as in Rhizobium and legumes, where the bacteria provides the plant with nitrogen, while the plant supplies nutritients.

The secretory system has substantial homologues with the flagellum (Hueck 1998), and some critics imagine the simple secretory system as a precursor to the more complex flagellum. This, however, is at odds with the concensus of the scientific community, which is that it was the secretory system that evolved from the flagellum, not the other way around (e.g. Stephens & Shapiro 1996; Macnab 1999; Nguyen 2000), though see Gohpna, Ron & Graur (2003) for a dissenting opinion and Saier (2004) for a response. Contrary to acting as a "steppping stone" in the evolution of flagella, the secretory system is the result of reducing selection, a common fate for organisms living in close symbiotic relationships (Andersson & Andersson 1999).

Conclusion

The examples discussed in this essay illustrate how alluring the equation between simplicity and primitiveness can be, especially when seen from the Darwinian perspective. However, they also illustrate the problems with an approach used by many critics of intelligent design. Often, it is asserted that teleologists need to show that Darwinian scenarios are impossible or in other ways show that design is "necessary". In this regard, they face a demand similar to that made by Darwin, who, in proposing his scenario for lung evolution, noted that "there seems to me to be no great difficulty in believing that natural selection has actually converted a swimbladder into a lung, or organ used exclusively for respiration" (1859, 191). Well, Darwin was right about that: The evolution of lungs from swim bladders isn't impossible - I certainly know of no law of nature that prevents it. But Darwin was also wrong: Although the lung could have evolved from the swim bladder, it didn't. Similarily, in none of the examples discussed above was a new phylogeny established by showing that the old one was impossible. Finding "in principle" reasons is for philosophers, while detailing history involves determining the actual course of events. Therefore, intelligent design, in striving to produce a historical narrative of life, is not going to be cut down by people raising philosophical objections.

References