Worm Genes Show Non-Evolutionary Pattern

first_imgBiologists at New York University compared genes of roundworms to look for evidence of evolutionary ancestry.  What they found was not what they expected.  They found more genetic variation between outwardly-similar worms than between mice and men.  Their results were published online in PNAS June 7.1    The roundworm Caenorhabditis elegans is a model lab organism for genetic studies.  Kiontke et al. compared it with 7 other worms of the same genus and four other related species.  They first devised a family tree of the worms, based on commonly-accepted phylogenetic techniques.  Despite the fact that only subtle morphological differences exist between most of the species, they found major differences in intron counts (with intron loss apparently much more frequent than intron gain).  They also deduced that a specialized form of hermaphroditism (ability to self-fertilize) evolved separately in two species, C. elegans and C. briggsae, by convergent evolution.  Summarizing all the differences they found, they stated with obvious surprise that “despite the lack of marked morphological diversity, more genetic disparity is present within this one genus than has occurred within all vertebrates.”    The amount of genetic diversity between these worms is all the more surprising considering the impact one change can sometimes have.  In another paper published in PNAS the same day,2 a team of scientists studied a genetic disease called progeria that makes children die of old age at 13.  The disease is caused by a single point mutation in one spot, the lamin A gene, that is important in maintaining the structure of the nucleus.    Why the worms show so much genetic diversity despite little outward visible difference was puzzling to the biologists.  They postulated it might be due to stabilizing selection (influences that, despite genetic changes, produce results analogous to treading water or running in place).  Alternatively, “developmental constraints may limit the ‘evolvability’ of Caenorhabditis,” they suggested.  Or maybe the worms’ molecular clock ticks at much higher rates than in higher organisms, although they dispute the idea.    They leave it as an unsolved puzzle how similar-looking worms could show more genetic diversity than vertebrates (including mice, rats, hamsters, zebrafish and humans).  “It had been noted previously that the genetic distance between humans and chimpanzees seemed too small to account for their substantial organismal differences.  However,” they observe, “the situation is strikingly reversed in Caenorhabditis.”1Kiontke et al., “Caenorhabditis phylogeny predicts convergence of hermaphroditism and extensive intron loss,” Proceedings of the National Academy of Sciences USA, 10.1073/pnas.0403094101, published online before print June 7, 2004.2Goldman et al., “Accumulation of mutant lamin A causes progressive changes in nuclear architecture in Hutchinson-Gilford progeria syndrome,” Proceedings of the National Academy of Sciences USA, 10.1073/pnas.0402943101, published online before print June 7, 2004.Molecular phylogenetics is not providing the evidence of common ancestry for which evolutionists had hoped.  Since it looks like an exercise in futility, can we move on to better things now? (see yesterday’s headline, for instance.)(Visited 5 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img