An Evolutionary Origin of the Centrosome?
According to today's ScienceDaily, "New Evidence Suggests a Symbiogenetic Origin for the Centrosome."
But the evidence suggests no such thing. Instead, it points to the willingness of evolutionary biologists to believe just-so stories, and to the ideological corruption of the National Institutes of Health and the Proceedings of the National Academy of Sciences USA.
Centrosomes ("central bodies") are fascinating organelles. In undividing eukaryotic cells one is located next to the nucleus, where it serves as the organizing center for microtubules that make up the "cytoskeleton." The cytoskeleton gives the cell its shape and serves as the highway system along which many intracellular components are transported to their proper locations. (See the cell animation sequence in the movie "Expelled.") Just before cell division the centrosome duplicates, and the two centrosomes then form the poles of the cell division "spindle," a very complex apparatus composed of microtubules that emanate from the centrosomes. The spindle distributes chromosomes to the daughter cells, each of which also inherits one centrosome.
Even though centrosomes control many features of the cell (such as its morphology and the process of division), they are of much less interest to neo-Darwinists than cell nuclei, because centrosomes contain no DNA , so they cannot provide the DNA mutations that are assumed to be the raw materials for evolution. Thus many aspects of centrosomes, including their chemical composition, structure, function, and mode of replication--not to mention their origin--are (in the jargon of we-now-know-almost-everything Darwinists) "poorly understood."
Along come Mark and Mary Anne Alliegro of the Marine Biological Laboratory in Woods Hole, Massachusetts. In the abstract of an article published online May 5 by the Proceedings of the National Academy of Sciences USA (the complete article is not yet available, except to PNAS subscribers), the Alliegros report that some RNAs they extracted from surf clams are "centrosome-associated transcripts representing a structurally unique intron-poor collection of nuclear genes." Since a subset of these RNAs "contain functional domains that are highly conserved across distant taxa," the Alliegros conclude that they may "serve as cytological progenitors of the centrosome and may support a symbiogenetic model for its evolution."
Wait a minute. As the ScienceDaily press release explains, "only two cellular components--the mitochondria and the chloroplasts--are generally accepted by evolutionary biologists as having a symbiogenetic origin." This is because only mitochondria and chloroplasts (as far as we know) contain DNA that is inherited independently of the nuclear DNA. Since these tiny organelles contain DNA and look a bit like bacteria, the hypothesis of symbiogenesis asserts that they were once free-living prokaryotes that were engulfed by other prokaryotes to form eukaryotic cells. The hypothesis has lots of evidentiary problems, but whatever plausibility it seems to have with regard to mitochondria and chloroplasts completely evaporates in the case of centrosomes.
The problem is not just that centrosomes contain no DNA. The most solidly established function of centrosomes is that they serve as the organizing centers for microtubules, but microtubules occur only in eukaryotes, not in prokaryotes. Furthermore, centrosomes in animal cells contain two turbine-like centrioles oriented at a right angle to each other. Nobody knows for sure what centrioles do, nor why they occur in orthogonal pairs, and their origin is a complete mystery. There is no evidence that centrosomes or centrioles ever existed -- or ever could have existed -- in anything other than eukaryotic cells. The idea that free-living centrosome-like organisms were once engulfed by other primitive organisms is about as implausible as you can get, and the implausibility is not lessened by the presence in centrosomes of RNAs "that are highly conserved across distant taxa."
In this case, evolutionary jargon has taken the place of clear thinking. Yet the National Institutes of Health supported this medically useless speculation with our tax dollars, and the Proceedings of the National Academy of Sciences USA elevated it to the status of "peer-reviewed" science--part of the "overwhelming evidence" for evolution.
1 W. F. Marshall and J. L. Rosenbaum, "Are There Nucleic Acids in the Centrosome?" Current Topics in Developmental Biology 49 (2000): 187-205.