Eukaryote Evolution Proceeded from Complex to Simple
As if reprimanding simpletons, three scientists writing in Science1 preached that the old picture of evolution from simple to complex is simplistic. This is particularly true, they claim, for the story that eukaryotes were born from a blessed union. “Data from many sources,” they counter, “give no direct evidence that eukaryotes evolved by genome fusion between archaea and bacteria.” Further down, they remark, “Unfortunately, such a model has been tacitly favored by molecular biologists who appeared to view evolution as an irreversible march from simple prokaryotes to complex eukaryotes, from unicellular to multicellular.” The old picture harks back to obsolete views of straight-line evolution.
Comparative genomics and proteomics have strengthened the view that modern eukaryote and prokaryote cells have long followed separate evolutionary trajectories. Because their cells appear simpler, prokaryotes have traditionally been considered ancestors of eukaryotes. Nevertheless, comparative genomics has confirmed a lesson from paleontology: Evolution does not proceed monotonically from the simpler to the more complex. Here, we review recent data from proteomics and genome sequences suggesting that eukaryotes are a unique primordial lineage….
Out with the old, in with the new. What do they suggest to replace the old picture? Believe it or not, “sequence loss and cellular simplification.” Since these are “are common modes of evolution,” they argue that the first eukaryote was already a unique, complex creature. Like a predator or raptor, it acquired mitochondria by phagocytosis, and diversified from there.
Their view does not prohibit increases in complexity, yet they seem eager to distance evolutionary theory from visions of progress. “Genome evolution is a two-way street,” they say; “This bidirectional sense of reversibility is important as an alternative to the view of evolution as a rigidly monotonic progression from simple to more complex states, a view with roots in the 18th-century theory of orthogenesis.” They describe several life-forms that have reduced their genomes and slimmed down to the bare minimum: parasites, symbionts, organelle genomes, and anaerobes.
OK so far; evolution can move either toward complex or simple – but how does this explain eukaryotes (cells with nuclei and compartmentalized organelles)? Here, their explanation appears forced by the hard realities of the evidence. From the earliest possible ancestor, eukaryotes were already complex. They had introns (and complex spliceosomes, half of whose 78 proteins are unique to eukaryotes, to handle them), mitosomes, hydrogenosomes, mitochondria, nuclei, nucleoli, the Golgi apparatus, centrioles, and an endoplasmic reticulum, along with “hundreds of proteins with no orthologs evident in the genomes of prokaryotes.” (Simple Giardia, for example, has 347 eukaryote signature proteins.) Much of the article describes the unprecedented features of eukaryotes, which constitute a “unique cell type that cannot be deconstructed into features inherited directly from archaea and bacteria.”
This calls for alternatives to “hypotheses that attribute eukaryote origins to genome fusion between archaea and bacteria” (endosymbiosis), which they claim “are surprisingly uninformative about the emergence of the cellular and genomic signatures of eukaryotes.” Recognition of these realities must be “the critical starting point” for explaining where eukaryotes came from: i.e., a “larger and more complex cell” at the beginning when the three kingdoms – bacteria, archaea and eukaryotes – diverged.
Their picture can be summarized as follows: (1) the common ancestor was a raptor or predator on prokaryote mitochondria. (2) Cellular crowding and compartmentalization led to more efficient molecular interactions. (3) Extensive genome reduction followed. Darwin, of course, grins in the background; “This abbreviated account of genome reduction illustrates the Darwinian view of evolution as a reversible process in the sense that ‘eyes can be acquired and eyes can be lost’” (because of the two-way street of natural selection). Even Darwin would have agreed that “selection gives, and selection takes.” They concur with essential evolutionary doctrine without hesitation: “Genomes evolve continuously through the interplay of unceasing mutation, unremitting competition, and ever-changing environments.” Darwinism is safe, therefore; so now, let’s picture the new emerging story for the 21st century:
For the reasons outlined above, we favor the idea that the host that acquired the mitochondrial endosymbiont [sic] was a unicellular eukaryote predator, a raptor. The emergence [sic] of unicellular raptors would have had a major ecological impact on the evolution of the gentler descendants of the common ancestor. These may have responded with several adaptive strategies: They might outproduce the raptors by rapid growth or hide from raptors by adapting to extreme environments. Thus, the hypothetical eukaryote raptors may have driven the evolution of their autotrophic, heterotrophic, and saprotrophic cousins in a reductive mode that put a premium on the relatively fast-growing, streamlined cell types we call prokaryotes.
One problem. How this complex, predatory cell with most of its unique parts “emerged” is anyone’s guess. So get busy, everyone: “This scenario, which is not contradicted by new data derived from comparative genomics and proteomics, is a suitable starting point [sic] for future work.”
1Kurland, Collins and Penny, “Genomics and the Irreducible Nature of Eukaryote Cells,” Science, 19 May 2006: Vol. 312. no. 5776, pp. 1011 – 1014, DOI: 10.1126/science.1121674.
How many more times can Darwinism survive the onslaught of facts? Here is another case where (1) everything you know is wrong, (2) the old ideas taught in the days of the Scopes Trial and as far back as Darwin were too simplistic, (3) the complexity appears to have been present from the start, and (4) nobody has a clue what happened, and (5) all we have is a “suitable starting point” (read: hunch, guess, scenario, plot, tall tale) for starting all over. Once again, also, it will be harder this time because the “new data derived from comparative genomics and proteomics” complicates the picture enormously.
In place of the old simple story (that was easy to illustrate in textbook cartoons), we have a new, more violent tale. Predator cells pop into existence somehow, fully equipped; they alter the ecology and force the prokaryote prey to streamline their genomes and hide. Established at the top of the food chain, these new eukaryotes begin their long trek toward Volvox, Tiktaalik and Homo sapiens. Whenever needed, these storytellers can always invoke the Darwinist Miracle Word emergence to cover their tracks, and call in Tinker Bell to wave the mutation wand when a major innovation is needed. Thus is worship in the Temple of Charlie kept going another day, while Big Science mans the fortifications. But for how much longer? The Visigoths are at the gates (05/09/2006), demanding, “Enough of this! No more excuses. Mr. Darwin, tear down this wall!”